United States 

Department of 

Agriculture

Animal and 

Plant Health

Inspection Service

Agricultural Research 

Service

US Forest Service

Cooperating State 

Departments of 

Agriculture

Emerald Ash Borer 

Biological Control 

Release and Recovery 

Guidelines 2021
i

Emerald Ash Borer, Agrilus planipennis (Fairmaire), Biological Control 

Release and Recovery Guidelines 2021

Prepared by:

Juli S. Gould, Entomologist and Theresa Murphy, Biological Technician

USDA APHIS PPQ S&T Laboratory Juli.R.Gould@usda.gov

508-563-0923

Benjamin Slager,

USDA APHIS PPQ, EAB Biocontrol Rearing Facility Benjamin.h.slager@usda.gov

810-844-2704

Leah S. Bauer, Research Entomologist Emeritus

USDA Forest Service, Northern Research Station leah.bauer@usda.gov

517-884-8059

Jian Duan, Research Entomologist

USDA ARS Beneficial Insects Introduction Research Unit Jian.Duan@usda.gov

302-731-7330 ext. 249

Toby Petrice, Entomologist

USDA Forest Service, Northern Research Station toby.petrice@usda.gov

517-884-8058

ACKNOWLEDGEMENTS

Substantial contributions to the methods for rearing parasitoids and conducting field sampling were 

provided by: Ben Slager, Tracy Ayer, Houping Liu, Debbie Miller, Phil Taylor, Kristopher Abell, 

Jason Hansen, and Michael Ulyshen.

Thank you to the following for providing critical input in the development of this document: Joe 

Beckwith, James Buck, Russ Bulluck, Sharon Lucik, Michael Winks.

Cover photographs by: Top left: David Cappaert, Contractor, Michigan State University (T. 

planipennisi); Middle right: Tracy Ayer, Technician, USDA APHIS PPQ CPHST (S. agrili); Bottom 

left: Deborah Miller, Entomologist, USDA FS NRS (O. agrili)

Cite this report as follows: USDA–APHIS/ARS/FS. 2021. Emerald Ash Borer Biological Control 

Release and Recovery Guidelines. USDA–APHIS–ARS–FS, Riverdale, Maryland
ii

Contents

ACKNOWLEDGEMENTS ....................................................................................................................................................I

INTRODUCTION BRIEF HISTORY OF EAB IN NORTH AMERICA......................................................................... 1

LIFE-CYCLE OF EAB ........................................................................................................................................................ 1

DAMAGE AND SIGNS OF INFESTATION...................................................................................................................... 2

ECONOMIC CONSEQUENCES OF EAB INFESTATIONS............................................................................................. 3

HOST RANGE OF EAB...................................................................................................................................................... 4

BIOLOGICAL CONTROL OF EMERALD ASH BORER............................................................................................... 4

BIOLOGY OF EAB BIOCONTROL AGENTS .................................................................................................................. 4

REARING EAB PARASITOIDS......................................................................................................................................... 6

PROJECT STATUS............................................................................................................................................................. 7

PREPARATION FOR PARASITOID RELEASE............................................................................................................... 7

FIELD RELEASE .................................................................................................................................................................. 8

OUTLINE OF PROCEDURES FOR EAB BIOCONTROL RELEASES............................................................................ 8

RELEASE SITE SELECTION............................................................................................................................................. 9

PRE-RELEASE SITE ASSESSMENT .............................................................................................................................. 12

PRE-RELEASE SITE PREPARATION ............................................................................................................................ 14

RELEASE OF PARASITIODS........................................................................................................................................... 14

RELEASE CONSIDERATIONS: WHICH SPECIES, WHERE, WHEN.......................................................................... 14

Tetrastichus planipennisi............................................................................................................................................... 15

Spathius galinae............................................................................................................................................................. 16

Spathius agrili................................................................................................................................................................ 16

Oobius agrili.................................................................................................................................................................. 16

REQUESTING PARASITOIDS........................................................................................................................................ 17

RECEIPT OF PARASITOIDS........................................................................................................................................... 17

CARE OF PARASITOIDS IF RELEASE IS DELAYED .................................................................................................. 18

TRANSPORTING PARASITOIDS TO FIELD SITES ..................................................................................................... 18

RELEASE OF PARASITOIDS.......................................................................................................................................... 19

ENTER RELEASE DATA................................................................................................................................................. 20

EVALUATING PARASITOID ESTABLISHMENT........................................................................................................ 21

TREE FELLING AND DEBARKING............................................................................................................................... 22

DEBARKING .................................................................................................................................................................... 22

Recovering the Egg Parasitoid Oobius from Outer Bark Samples:............................................................................... 23

Peeling Logs to Recover Larval Parasitoids:................................................................................................................ 25

YELLOW PAN TRAPS..................................................................................................................................................... 26

PROCESSING YELLOW PAN TRAP SAMPLES........................................................................................................... 31

PHOTO GUIDE TO IDENTIFYING EAB PARASITOIDS IN YELLOW PAN TRAPS ............................................ 37

TETRASTICHUS PLANIPENNISI (EULOPHIDAE)........................................................................................................................ 37

OOBIUS AGRILI (ENCYRTIDAE) ............................................................................................................................................ 41

SPATHIUS SPECIES (BRACONIDAE)....................................................................................................................................... 43

ATANYCOLUS SP. .................................................................................................................................................................. 46

ENTER RECOVERY DATA .............................................................................................................................................. 46

Appendix A- EAB Life Stages and Damage

Appendix B- Parasitoid Life Stages 

Appendix C- Crown Condition of Ash Trees

Appendix D- Helpful Links

Appendix E- Releasing Parasitoids for Optimal Establishment 
1

INTRODUCTION BRIEF HISTORY OF EAB IN NORTH AMERICA

Emerald ash borer (EAB), a beetle from Asia that feeds on ash trees, was discovered as the cause of 

extensive ash mortality in southeast Michigan and adjacent areas of Canada in 2002. It is thought that 

this destructive pest was introduced in the early 1990’s in infested solid wood packing material 

originating in Asia.

Shortly after EAB was discovered in North America, federal and state regulatory agencies placed 

infested counties under quarantine and eradication activities were initiated. Due to the magnitude of the 

EAB infestation in North America, the potential for natural and artificial dispersal of EAB, limited 

EAB detection and control methods, and high costs, program objectives shifted away from eradication 

to containment and management of the pest. As of March 2020, EAB infestations in the U.S. were 

known in Alabama, Arkansas, Colorado, Connecticut, Delaware, District of Columbia, Georgia, 

Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, 

Minnesota, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, Ohio, 

Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, 

Virginia, West Virginia, and Wisconsin and the Canadian provinces of Manitoba, New Brunswick, 

Nova Scotia, Ontario, and Québec. At present, the most sustainable and long-term approach to 

reducing EAB populations and conserving ash in forested areas of North America is biological control.

LIFE-CYCLE OF EAB

EAB takes one or two years to complete its life-cycle depending on temperature, latitude, altitude, local 

population density, and tree health. Below is a description of the one-year EAB life-cycle:

Adults

EAB adults begin to emerge from ash trees after the accumulation of 400-500 growing degree days 

base 50°F (GDD50F). Peak adult activity occurs at ~1,000 GDD. After emergence, adults fly into the 

ash canopy where they feed on leaves throughout their lives. EAB adults start mating one week after 

emergence, and females begin laying eggs 2-3 weeks later. In the field, EAB adults are readily 

observed mating and egg-laying on ash trees on warm, sunny afternoons. The adults of both sexes are 

strong fliers.

Eggs
2

A female EAB may lay >200 eggs in her lifetime, depositing them individually or in groups on the bark 

along the trunk and portions of major branches. Eggs are laid in areas where the bark is rough, and 

between bark layers or in bark crevices. Eggs are approximately 1.0 mm long x 0.6 mm wide and 

creamy white when laid; fertile eggs gradually turn amber after a few days (Appendix A). The eggs 

hatch after two to three weeks.

Larvae

Newly hatched larvae bore through the bark to the phloem and outer layer of new sapwood where they 

feed until the weather gets too cold in the fall. There are four stages of larval development (instars) 

(Appendix A). As they feed, the larvae create serpentine galleries filled with frass (excrement), which

enlarge in width as the larvae grow (Appendix A). Larvae are creamy white, and dorso-ventrally 

flattened (Appendix A). When fully mature, 4th-instar larvae are 26 to 32 mm long. The head is mostly 

retracted into the prothorax with only the dark brown mouthparts visible. The prothorax is enlarged, 

with the mesothorax and metathorax slightly narrower. Larvae have 10 bell-shaped abdominal 

segments and a posterior pair of small brown structures called urogomphi (Appendix A).

Overwintering larvae, prepupae, pupae, and adults

In the fall, mature 4th-instar EAB larvae excavate pupal chambers in the new sapwood or outer bark 

where they fold into overwintering “J-shaped larvae” (Appendix A). In winter and spring, the J-shaped 

larvae shorten into prepupae then shed their cuticle to become naked pupae. Pupae are initially creamy 

white, but the eyes turn red and the body darkens as they develop to the adult stage (Appendix A). To 

emerge from ash trees, adults chew D-shaped exit holes (Appendix A) through the bark and are 

immediately capable of flight upon emergence. EAB larvae that are immature as cold weather arrives 

in the fall will simply overwinter in their larval feeding gallery. Mature larvae complete development 

(i.e. become an adult beetle) the next spring, whereas younger larvae may require another summer of 

feeding, becoming adult beetles the following spring.

DAMAGE AND SIGNS OF INFESTATION

EAB larvae damage ash trees by feeding on the phloem. In a new infestation, when just a few EAB 

larvae infest a tree, the tree responds by forming scar tissue or “callus” around EAB galleries, and the 

tree may show few outward signs of infestation. On some trees or branches, however, the callus may 

cause the bark to split open, exposing the EAB gallery beneath (Appendix A). As EAB larval 
3

population density increases, the movement of nutrients through the phloem is disrupted and evidence 

of tree stress increases such as yellow foliage on dying branches, dead branches, small leaves, thinning 

crowns, and epicormic shoots (Appendix A). Woodpeckers feed on EAB larvae living under the bark 

of trees.

Field observations suggest woodpecker feeding is one of the best indicators of early EAB infestation 

with the most obvious symptoms including bark scaling (removal of bark flakes) or ‘blonding’ due to 

the exposed bark being lighter in color and feeding holes through the bark (Appendix A). Although 

difficult to detect, especially high in the canopy, the D-shaped exit holes chewed by emerging adults 

are diagnostic indicators of EAB infestation (Appendix A).

ECONOMIC CONSEQUENCES OF EAB INFESTATIONS

The cost of managing EAB is already high. On average, federal and state resource managers spend at 

least $29.5 million per year to manage EAB populations. The compensatory value of the 8 billion ash 

trees in U.S. timberland potentially infested with EAB is $282 billion. States in the eastern U.S. 

produce nearly 114 million board feet of ash saw timber annually, with a value of $25.1 billion. White, 

black, and green ash make up >7 percent of the hardwood stand mix and 5.5 percent of the total stand 

mix (including conifers) in the northeastern United States and eastern Canada. The wood is used for a 

variety of applications including tool handles, baseball bats, furniture, cabinetry, solid wood packing 

materials, pulp, and paper. Native Americans utilize black ash for basketry, which is both economically 

and culturally important. The continued spread of EAB threatens our ash resources and will 

permanently alter forest ecosystems in North America. The 16 native species of ash, some with limited 

distributions in North America, are now threatened by EAB.

In addition to its value to the timber industry and the forest ecosystem, ash was one of the most popular 

landscape trees because of its tolerance of a range of environmental conditions and resistance to pests. 

Ash was the most commonly planted tree species used to replace elm trees decimated throughout North 

America by Dutch elm disease and for new residential and commercial developments. The estimated 

cost of treating, removing, and replacing 37.9 million ash trees in urban and residential settings in 25 

states for one decade (2009-2019) was estimated at $25 billion.

Nationwide, the nursery industry produced an estimated 2 million ash trees each year. With median 

approximate values ranging from $50 to $70 per tree, the annual ash nursery stock was worth between 

$100 and $140 million.
4

HOST RANGE OF EAB

In North America, EAB attacks ash species in the genus Fraxinus, including but not limited to green 

ash (F. pennsylvanica), white ash (F. americana), black ash (F. nigra), pumpkin ash, (F. profunda), 

and blue ash (F. quadrangulata). In China, native ash species, including Chinese ash (F. chinensis) and 

Manchurian ash (F. mandshurica), are less susceptible to EAB than North American species commonly 

planted in China such as velvet ash (F. velutina) and green ash (F. pennsylvanica). In 2014, EAB was

observed attacking North American white fringetree, Chionanthus virginicus L. in Dayton, Ohio. 

However, the impact of EAB on white fringetree is not yet well understood.

BIOLOGICAL CONTROL OF EMERALD ASH BORER

Biological control (or biocontrol) is the practice of importing and releasing natural enemies from a 

pest’s native range to control the target pest populations in the area of introduction. Biocontrol has been 

used for over 100 years in the U.S. and has successfully controlled invasive plant and insect pests such 

as gypsy moth, winter moth, ash whitefly, eucalyptus longhorned borer, purple loosestrife, and 

Klamath weed. Because EAB is from northeast Asia, U.S., Chinese, and Russian scientists have been 

searching for EAB and its natural enemies in that region since 2003. In Asia, EAB population densities 

are relatively low due to the combined effects of EAB-resistance in Asian ash species, scarcity and 

patchiness of forests, and the EAB natural enemy complex. Exploration for EAB natural enemies in 

China, Russia, and Korea has yielded several hymenopteran parasitoids, and four species have been 

approved for release as biological control agents of EAB in the U.S and others are under consideration.

BIOLOGY OF EAB BIOCONTROL AGENTS

Oobius agrili parasitizes up to 60% of EAB eggs laid during the summer in some areas of China. Tiny 

female Oobius accomplish this by searching the bark of ash trees for EAB eggs. When Oobius finds an 

EAB egg, it injects its own egg inside (Appendix B) where it will hatch, grow, and kill the host egg. 

All Oobius being released are females that reproduce without mating to produce only daughters. 

Oobius adults will emerge and repeat the cycle for at least two generations during the EAB egg-laying 

season. Each Oobius adult parasitizes up to ~80 EAB eggs during its lifetime. Oobius spend the winter 

as larvae inside EAB eggs and emerge as adults the following spring.
5

Spathius agrili parasitizes up to 90% of EAB larvae in ash trees east of Beijing in Tianjin, China, 

where the climate is relatively mild, thus releases of S. agrili are limited to EAB infestations in the 

south, where EAB also has a one-year life cycle like that of EAB in Tianjin, China. Spathius agrili is 

now released in areas where at least 50% of the EAB have a one-year life cycle which modelling 

predicts will be in areas that accumulate more than 3,500 GDD 50F (Appendix E). Female Spathius 

parasitize EAB larvae by drilling through the bark (Appendix B) and laying an average of 8 eggs on the 

outside of its host while simultaneously paralyzing the EAB. The hatching parasitoid larvae (Appendix 

B) feed and develop on the EAB larva, causing its death. The cycle is repeated 1-2 times each summer 

and fall depending on climate. Spathius agrili overwinter as larvae or pupae and enter obligate 

diapause in the host gallery. Mature larvae spin silken cocoons in which they pupate and emerge as 

adults during the following summer.

Tetrastichus planipennisi is another larval parasitoid of EAB collected from China. The life cycle of 

Tetrastichus is similar to that of Spathius, however, the female parasitoid lays eggs inside EAB larvae 

where the parasitoid larvae grow, eventually killing their host. Tetrastichus completes several 

generations each year, and one EAB larva can produce up to 130 Tetrastichus adults. They survive the 

winter under the bark of ash trees as larvae inside their host or as prepupae in their host gallery

(Appendix B). As the weather warms in spring, the overwintering larvae of Tetrastichus gradually 

pupate, develop into adults, emerge from small round exit holes chewed in the bark above the gallery, 

and seek EAB larvae to parasitize. Due to the short ovipositor of Tetrastichus, they are more successful 

in parasitizing EAB larvae in small diameter ash sapling and trees up to ~6 inches in diameter at breast 

height (DBH). Research has shown that for Tetrastichus populations to persist they need EAB larvae to 

parasitize when they emerge in the spring. Tetrastichus is now preferentially released in areas where at 

least 25% of the EAB have a two-year life cycle and where modelling predicts Tetrastichus will 

establish (Appendix E). 

Spathius galinae has a biology similar to that of S. agrili, however, S. galinae originated in the Russian 

Far East and may complete two or more generations per year. The Russian Far East is more 

climatically similar to northern regions of North America than to the region of China where S. agrili

was collected, thus S. galinae is more likely to establish further north than S. agrili. In addition, both S. 

galinae and T. planipennisi are more likely to establish in northern regions due to the availability of 

EAB larvae early in the spring when their adults emerge seeking hosts. Spathius galinae is expected to 

fill an important niche because its long ovipositor allows it to parasitize EAB larvae in large diameter 

ash trees (up to ~23 inches DBH).
6

REARING EAB PARASITOIDS

The USDA APHIS PPQ Biological Control Production Facility in Brighton, MI produces EAB 

parasitoids for field release. These small parasitic wasps must be reared in EAB eggs or larvae, which 

are produced or harvested from ash trees felled and removed from EAB-infested woodlots. Although 

the parasitoids are reared and stockpiled throughout the year for release during the field season, the 

rearing methods are time and labor intensive. Research is ongoing on an artificial diet for EAB, but for 

now fresh logs and leaves are needed for production of EAB and its parasitoids. There are also 

challenges storing the Spathius species in chill for stockpiling prior to release.

The EAB egg parasitoid, Oobius agrili, is reared in EAB eggs laid on paper by 

EAB adults. Oobius will be shipped to cooperators either as mature pupae inside 

EAB eggs on paper held inside pill vials with screening (Oobinators) or as 

adults in plastic cups with solid caps. Oobius pupae are released by attaching 

the Oobinators to ash trees, with the screen-side down, and removing the plastic 

cap. The Oobius adults will emerge and disperse naturally. Oobius adults are 

released from the plastic cups by opening the lids, inverting the cup, and tapping 

it gently against the trunks of EAB-infested ash trees at release sites.

The three species of EAB larval parasitoid, S. agrili, S. 

galinae, and T. planipennisi, are reared in small ash bolts in 

which EAB larvae are grown from eggs applied to the bark. 

Although some Spathius and Tetrastichus adults may be 

shipped in plastic cups, most of the larval parasitoids are 

shipped as mature pupae in the small ash bolts. These bolts 

will be shipped with a small hole drilled through the top to 

provide a point of attachment to a release tree. Twine or zip 

ties are common materials used to attach release bolts. 

Spathius galinae will be shipped exclusively as adults in 

cups due to the difficulty in getting S. galinae to emerge 

from bolts that have been kept in storage for several months. 

Spathius or Tetrastichus adults are released from the plastic 

cups by opening the lids, removing the screening, inverting 

the cup, and tapping it gently against the trunks of EAB-infested ash trees at release sites.

Ash bolt with parasitized EAB

Oobinator
7

PROJECT STATUS

Since EAB parasitoid releases began in 2007, researchers have found that Tetrastichus planipennisi 

and Oobius agrili have established in many states and provinces, are dispersing from the release sites, 

and are responding to changes in EAB density by increasing percentage parasitism. Spathius agrili is 

found periodically at some southerly release sites, but we are still in the early stages of release in the 

south. Release of Spathius galinae began in 2015, and its establishment and spread appear successful at 

long-term study sites in Connecticut, Massachusetts, Michigan, and New York. Another species of 

Oobius, reared from EAB eggs collected in Russia, is being evaluated as an EAB biocontrol agent for 

some regions of the U.S. and Canada. Over the last 10 years, the EAB Biocontrol Rearing Facility in 

Brighton, Michigan has produced and released more than 6 million parasitoids. Releases have occurred 

in 29 states (Arkansas, Colorado, Connecticut, District of Columbia, Delaware, Iowa, Illinois, Indiana, 

Kansas, Kentucky, Louisiana, Massachusetts, Maryland, Maine, Michigan, Minnesota, Missouri, 

Nebraska, New Hampshire New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, 

South Dakota, Tennessee, Virginia, Wisconsin and West Virginia) and 3 Canadian Provinces (New 

Brunswick, Ontario and Quebec).

PREPARATION FOR PARASITOID RELEASE

This section provides guidance for selecting parasitoid-release sites, collecting data on site 

characteristics, and releasing the parasitoids. For the EAB Biocontrol Program to monitor and evaluate 

the establishment of EAB parasitoids and the impact of EAB biocontrol, researchers and cooperators 

receiving parasitoids from USDA APHIS Biological Control Production Facility must agree to submit 

their release and recovery data to a centrally managed, online, 

geospatial, searchable database at www.mapbiocontrol.org .

Release data is to be entered into mapbiocontrol.org within 48 

hours after release. Accurate release and recovery data are critical 

to the continued success of the EAB Biocontrol Program. You must 

first register to gain access to mapbiocontrol.org, and after you 

login, you will be asked to agree to enter parasitoid release and 

recovery data into this central database. This database will store

data on where, when, how, under what conditions, and how many 

parasitoids were released and store data on possible parasitoids

MapBio available on Apple Store
8

recovered. Personnel are encouraged to use the MapBio app (available for iPads and iPhones) or they 

can also use a hand-held GPS device and/or hard copy datasheets to collect data in the field. The data 

from the MapBio app can be synchronized (uploaded to mapbiocontrol.org). Data written on hardcopy 

datasheets and hand-held GPS units must be entered online manually.

FIELD RELEASE

OUTLINE OF PROCEDURES FOR EAB BIOCONTROL RELEASES

• It is no longer necessary to obtain release permits. The EAB Biocontrol Rearing Facility has 

permits to release all four parasitoid species in all of the states currently infested with EAB.

• Select a release site in an area with good access, high density of ash trees of various sizes, and 

infested with EAB.

• Obtain Local Land-Use Permits

• Enter Data about the site location into MapBioControl (www.mapbiocontrol.org). Take site 

coordinates in the center of the plot where the releases will occur, as described above. Only one 

release site in a general area is needed to assess parasitoid establishment.

• Collect General Site Details and Physical Characteristics using an iPad/iPhone (you will need to 

download the MapBio app from the Apple Store) or manually enter the information into the 

MapBioControl web site (www.mapbiocontrol.org).

• Notify the EAB Biocontrol Program (EAB.Biocontrol.Program@usda.gov) that your site has 

been submitted to mapbiocontrol.org. 

• Synchronize your iPhone. If you are using an iPhone/iPad, the unit should be synchronized with

MapBioControl.org by selecting send/receive data every time data are collected to prevent the loss 

of data or data can be entered manually.

• Email Requests for Parasitoids at EAB.Biocontrol.Program@usda.gov once your site has been

approved.
9

• Collect Data on Release Trees (size, EAB density, tree health) using your iPhone/iPad with 

MapBio app installed or manually enter data online at www.mapbiocontrol.org.

• Release Parasitoids: Release at least the minimum recommended number of parasitoids in the 

spring, mid-summer, and late summer in Year 1 and Year 2 (See Parasitoid Release Section for 

details). Enter Release data using the MapBio app on your iPhone/iPad or online at

mapbiocontrol.org within 48 hours of release.

• Assess Parasitoid Establishment: Determine if the parasitoids are established in each general 

release area (not necessarily at each site) at least one year following the Year 2 release (Year 3 or 

more). This should be done during the fall, winter, or early spring (for bark sampling or log 

debarking) or late spring, summer, and early fall (for yellow pan traps). Several methods are 

available for parasitoid recovery, with the choice of method depending on the specific 

circumstances of each release site.

RELEASE SITE SELECTION

Although improved rearing methods have allowed for the production and release of greater parasitoid 

numbers than in the past, each parasitoid is still costly to produce. Therefore, parasitoids should be 

released at sites where they have the highest probability of establishment (Appendix E). The site 

information described below should be collected and entered into mapbiocontrol.org, and will help 

researchers and the Rearing Facility Manager determine which sites are most suitable for release and 

establishment of the parasitoids.

The guidelines below outline the best practices for establishment. Note that these are guidelines to 

selecting sites and that your site may not have ideal characteristics for each item listed below. 

However, your site may still be appropriate for releases if it has compensating characteristics. For 

example, the site may have low acreage, but its connectivity to other plots is high. If determining the 

suitability for a particular site is not straightforward, please email the rearing lab

(EAB.Biocontrol.Program@usda.gov) to note that you have found what you believe to be the most 

suitable release site for your county, even though it doesn’t meet all of the requirements below. 
10

General Site Characteristics

Locate parasitoid-release sites in naturally forested areas, woodlots, wooded wetlands, and riparian 

zones. To allow for parasitoid establishment and dispersal, do not select release sites that may be 

harvested or developed in the next 5 years. State, county, city, and township parks, recreation areas, 

and game areas are less likely to be disturbed. Avoid sites with excessive human activity, as well as 

sites along roads, trails, or railroad tracks, and in picnic areas, golf courses, and open park lands. Ash 

trees in such public areas may be treated with insecticides or removed.

Minimum Acreage

Wooded areas at least 40 acres in size are preferred as parasitoid-release sites. Smaller release sites 

(<40 acres) will require higher ash densities and ash corridors connecting the release sites to other 

wooded areas. Examples of ash corridors are rivers, ditches, highways, and fence rows. Use of these 

criteria will facilitate parasitoid reproduction, establishment, and dispersal to nearby areas.

Relative Density of Ash

If possible, at least 25% of the trees should be ash, but a higher percentage of ash would be even better. 

The percentage of ash can be estimated as ≤25%, 26-50%, 51-75%, or 76-100%.

Ash Tree Size Class

Ideally, parasitoid-release sites should contain a variety of ash size classes ranging from seedlings to 

mature trees. Older and highly stressed ash trees in a stand are generally attacked first by EAB and tend 

to die off more quickly. Although these trees are less likely to benefit from EAB biological control, 

they will provide a high density of EAB eggs and larvae, increasing the probability of parasitoid 

reproduction at the site. Smaller trees, saplings, and seedlings provide potential for regeneration of ash 

trees, and will support EAB and their natural enemies following the loss of larger ash trees in the stand. 

Tetrastichus, which has a short ovipositor, appears most likely to establish in areas with some smaller, 

thin-barked ash trees, where EAB larvae are more accessible.

Density of EAB
11

Low to moderate EAB-population densities are recommended for potential parasitoid-release sites. 

Unless there are many young trees in the vicinity, stands with dead and dying ash trees are not 

appropriate as release sites because ash and EAB may decline or crash before the parasitoids become 

well established. The most accurate method of estimating EAB density requires felling and peeling the 

bark from ash trees to count EAB present under the bark and along the trunk. This direct estimate of 

EAB density, however, is difficult, labor intensive, destructive, and counter-productive in areas where 

EAB density is low. Therefore, after EAB has been confirmed at a site, we recommend using an 

indirect EAB-density estimate based on the signs and symptoms of EAB infestation in ash trees.

During the winter, before spring leaf flush, the most apparent symptom of EAB attack on the trunks of 

ash trees is woodpecker feeding and sometimes bark scaling. As EAB densities increase, EAB 

symptoms readily visible lower on ash trunks include bark splits, D-shaped EAB adult exit holes, 

epicormic shoots, and stump sprouts (Appendix A). Symptoms of dead ash trees include bark that is 

falling off trees, leaving exposed galleries and D-shaped exit holes (Appendix A).

During the spring and summer when the trees have leaves, the condition of ash trees can be visually 

ranked according to the five crown-condition classes illustrating typical EAB- induced decline; crown 

condition 1 is a healthy canopy, 2, 3, and 4 show increasing decline, and 5 is dead crown (Appendix 

C). Overall, ash trees at a potential release site should be fairly healthy, with an average crown 

condition of 1 to 2 (healthy or mostly healthy) and only a few trees in condition classes of 4 to 5 (dying 

or dead). Other insects and diseases can cause ash canopy decline, epicormic sprouts and/or 

woodpecker feeding. Therefore, the presence of EAB must be confirmed at each potential release site.

This is done by selecting ash trees with signs of stress from a possible EAB infestation. On these 

potentially infested trees, remove sections of bark using a chisel or draw knife to confirm the presence 

of EAB galleries or EAB life stages (Appendix A). However, early in the EAB outbreak cycle when 

the density of EAB is low, most EAB will be higher on the trunks, thus confirmation may require 

felling and debarking ash trees in the stand.

Access and local use permits

Select release sites at locations that are relatively easy to access because personnel will need to visit the 

site periodically for parasitoid release and recovery activities. Obtain permission from land owners for 

use of the site to both release parasitoids and conduct recovery activities over a period of five years. 

Keep in mind that it may take months to obtain permission or land-use permits from land owners or 
12

park managers.

PRE-RELEASE SITE ASSESSMENT

Note: The MapBio app will work on an iPad but you need to search “iPhone only” apps to find it. It 

will not appear under iPad apps. Also some iPads have cellular service and GPS capabilities but not all 

do. You will need an iPad with a GPS to properly use the MapBio app. 

Prior to requesting parasitoids for release, we recommend collecting some preliminary data on site 

characteristics that will help the Biocontrol Rearing Facility Staff assess whether your site is 

appropriate for parasitoid release. General Site Details and Physical Details data can be collected with 

an iPhone or iPad (MapBio app) and can also be entered online at www.mapbiocontrol.org. The 

mapbiocontrol app, MapBio, can be downloaded onto iPhones/iPads to ease the data collection and 

entry burden. When collecting data using an iPhone/iPad, be sure that you are at the location where 

parasitoids will be released. Do not collect GPS coordinates next to the road. Ideally the parasitoids 

should be released in the center of the forest, or at least 100 m from the road or other non-forested 

areas. Once the data collected on the iPhone/iPad are synchronized by clicking send/receive data, 

Rearing Facility personnel can review the site and determine if the site is appropriate for release. The 

information provided, including location, size (number of acres or hectares), percentage ash, and EAB 

density will assist Rearing Facility personnel and state cooperators prioritize and select the best site(s) 

for parasitoid release.

To enter data about a new Release Site into MapBioControl, click on “Release” in the green banner. 

Click the “New” button in the upper gray table, and then enter the following data:

• Status: Select “Proposed” because the site has not yet been approved.

• State

• Date

• Site Name

• Site Location (Enter general information such as county, town, park name, 

address, major roads, etc.)

• Latitude (dd.dddddd)
13

• Longitude (dd.dddddd)

• Plot (whether it is a release or control plot)

• Type (program or research)

To continue entering data about your new site, click on the site in the upper table to highlight it (it will 

turn yellow). Then click on one of the tabs below. When you click on the General Details Tab or the 

Physical Details Tab you will need to highlight the line of blanks in the lower table (it will turn yellow) 

before you can click on the “Edit” button to enter the data. To see more information about each entry 

item hover the mouse over the category. Enter site characteristics data as follows:

General Details

• Size of wooded area in acres (you can use the measurement tools with Google Earth 

or ArcGIS Explorer)

• % ash (estimate: <25%, 25%, 50%, 75%, 100%)

• Dominant Tree Species 

• 2nd most Dominant Tree Species (if applicable)

• 3rd most Dominant Tree Species (if applicable)

• EAB Density (Low, Medium, High)

Low: EAB present but difficult to find.

Med: Trees are beginning to show signs of EAB infestation. 

High: >25% of trees show signs of EAB infestation.

Physical Details

• Topographic Position (Upper Slope, Mid Slope, Lower Slope, Level)

• Flooding (Dry all year, Seasonally Wet, Wet all Year)

• Degree of Isolation (Surrounded by non-woodland or connected to other 

woodlots)
14

PRE-RELEASE SITE PREPARATION

General Plot Design and tree selection

After a site is chosen for parasitoid release, locate the center of the release plot generally in the middle 

of the trees infested with EAB. Positive signs of EAB include woodpecker feeding, bark splits, 

epicormic shoots, poor crown condition, and/or D-shaped exit holes. This will be the parasitoid-release 

epicenter. 

Release trees should be large enough to support hanging ash bolts containing parasitoids and 

should be spread throughout the release plot. 

RELEASE OF PARASITIODS

RELEASE CONSIDERATIONS: WHICH SPECIES, WHERE, WHEN

Prior to 2012, the EAB Biocontrol Program provided S. agrili, T. planipennisi, and O. agrili to each 

state for release upon request. However, we now know that the establishment of all three parasitoids 

varies with geographic areas and they are not all suitable for releases in all states. Thus, we have made

new recommendations based on current research results (Appendix E).

In theory, a higher number and frequency of parasitoids released increases the probability of 

establishing stable parasitoid populations. In reality, the number and frequency of parasitoid releases 

are often limited by the resources that are available for parasitoid production. The minimum numbers 

of parasitoids recommended for release are listed below by species. The actual numbers shipped may

vary depending on total availability during any given week and the number of release sites requiring 

insects. Whenever excess parasitoids are available, they are often added to the original number of 

parasitoids that were requested. Each release will consist of a specified number of female parasitoids, 

although males are also included in shipments of adult parasitoids (for larval parasitoids only). 

Considering that weather patterns in any given year can impact the synchrony between availability of 

the appropriate stages of EAB and release timing, and severe weather events may reduce parasitoid 

survival, releases should be made during two consecutive years at each biocontrol release site.

Larval parasitoids should be released when late-instar EAB larvae (3rd- and 4th-instar larvae) are 
15

present in the field. Making firm recommendations on release timing is difficult because EAB larval 

development is variable and depends on factors such as when the eggs were laid, temperature, and ash 

tree health. In addition, Oobius should be released when EAB eggs are present. However, EAB eggs 

are very small and nearly impossible to find in the field, and EAB larvae are under ash bark and not 

always accessible without felling trees. Spreading releases out over multiple weeks should help ensure 

that the proper stages of EAB eggs and larvae are present for parasitism. Growing degree day 

accumulations and forecasts can be found at http://uspest.org/US/ and http://uspest.org/cgibin/ddmodel.us

Below is a discussion of when and where to release each parasitoid species.

Tetrastichus planipennisi

 Tetrastichus planipennisi will be preferentially released at locations that accumulate fewer than 

3,500 GDD50F between January 1 and September 30. This corresponds to the part of the 

United States where 26-80% of EAB overwinter as larvae (close to the surface of the tree) 

rather than as J-larvae (in pupal chambers in the wood) and are available for parasitism in the 

spring. While in past years we suggested that the 40th parallel generally predicts this 

demarcation, we now have a model that delineates the areas expected to have over 25% EAB 

overwintering as larvae shown in Appendix E.

 If your site accumulates > 3,500 GDD50F in the summer and you would still like to release T. 

planipennisi please contact the rearing facility. You will need to confirm that you have 3-4thinstar EAB larvae in late winter or early spring before scheduling T. planipennisi releases. If 

between 3,500 and 3,975 GDD50F accumulate at your site between January 1 and September 

30 then you can expect to have between 11-25% of EAB overwintering as larvae.

 We rarely see establishment of T. planipennisi at sites where >3,975 GDD50F accumulate in 

the summer, and we do not recommend releasing this species in these locations.

 Tetrastichus planipennisi has a short ovipositor. Make sure there are plenty of trees and 

branches less than 6 inches in diameter at your site that contain EAB larvae before releasing.

Saplings and branches need to be over 1 inch in diameter to support EAB.

 Initiate releases in the spring after 300 GDD50F have accumulated. 

 Release again in the late summer-fall when mature larvae are available, generally between 1400 

and 2500 GDD50F.

 If you do not have any mature larvae in the spring, do not release T. planipennisi in the fall; 

there will be nothing for them to parasitize when they emerge in the spring.

 Release at least 200 females two weeks apart for 6 weeks (a minimum of 600 released per 
16

season – 1,200 per year).

Spathius galinae

 Counties in the northern U.S. where parasitoids, including S. agrili, were released but where S. 

agrili did not establish are eligible for release of S. galinae. A parasitoid with a longer 

ovipositor is needed to attack EAB in larger ash trees.

 Sites where the large ash trees have died are still suitable for release of S. galinae because it can 

attack EAB in smaller trees. But there must be plenty of live small ash trees available for EAB 

and its parasitoids for establishment to occur. Basal sprouts and saplings need to be over 1 inch 

in diameter to support EAB.

 Spathius galinae also emerges early in the spring and will only be released following the same 

guidelines as for T. planipennisi.

 Initiate releases in the spring after 300 GDD50F have accumulated. 

 Release again in the late summer-fall when mature larvae are available (generally between 1400 

and 2500 GDD50F). If you do not have any mature larvae in the spring, do not release S. 

galinae in the fall; there will be nothing for them to parasitize when they emerge in the spring.

 Release at least 100 females two weeks apart for 6 weeks (a minimum of 300 released per 

season – 600 per year).

Spathius agrili

 Spathius agrili will only be released at sites that accumulate more than 3,500 GDD 50F. It has 

not established in areas with fewer GDD. 

 Initiate releases when mature 3rd- and early 4th-instar EAB larvae are present in ash trees. That 

could be as early as mid-June (in southern states such as Arkansas) or in mid-July in more 

central states such as Tennessee. We do not yet have degree day estimates for initiating 

releases, and scraping some bark to find EAB and determine instars prior to release is 

recommended.

 Release at least 200 females per week for 6 weeks (1,200 total). 

 Do not conduct any releases after the end of August.

Oobius agrili

 Oobius agrili can be released in all states.

 Initiate releases at 600 GDD50F. Release at least 200 individuals per week for 3 weeks (600 

total). 

 Initiate the second round of releases at 1400 GDD50F. Release at least 200 individuals per 
17

week for 3 weeks (600 total). 

 Releases can continue until ~2,500 GDD50F have accumulated.

REQUESTING PARASITOIDS

Email all parasitoid requests to the EAB Biocontrol Program mailbox 

(EAB.Biocontrol.Program@usda.gov). If you have an emergency, please contact the Biological 

Control Release Coordinator – Scott Whitehead (810-844-2708) or the Facility Manager - Ben Slager 

(810-844-2704). You should enter data on the site characteristics and parasitoid releases into 

MapBioControl.org. Note: the Request Tab for parasitoid requests is currently under development and 

should not be used at this time.

RECEIPT OF PARASITOIDS

Parasitoids are shipped by overnight delivery in a cardboard box, and should arrive by 10:30 AM at 

most locations. Spathius and Tetrastichus will be shipped either as developing pupae inside ash bolts or 

as adults in 16-oz plastic cups with screening on the lid. Ash bolts will have a hole drilled through the 

log as a point of attachment for mounting on release trees. Twine, zip ties, and nails are commonly 

used attachment materials but are not included in parasitoid shipments. Honey will be smeared on the 

screening as a source of food for the adult parasitoids in cups. Adult Oobius will be shipped in plastic 

cups with honey streaked on the walls of the cup and sealed shut with a snap-top plastic lid lined with 

tissue paper. Oobius may also be shipped as pupae inside EAB eggs on paper held in small plastic vials that 

can be hung on ash trees at release sites. Be sure to remove the cap prior to deploying the vial so that 

the emerging parasitoids can escape. Small twist ties are fixed to these containers for hanging on small 

diameter branches, but this apparatus can also be attached to tree boles or larger diameter branches with 

twine, zip ties, or nails. 

The parasitoids should be released soon after receipt. All parasitoids should be released on the day 

they are received. If you are unable to release parasitoids as scheduled because of personnel shortages 

or adverse weather conditions, contact the Biological Control Release Coordinator to arrange for a 

different shipping date. After arrival, transport the parasitoids in the container to the release site. 

Oobius agrili do not fly as far as Tetrastichus and Spathius, so their release cups should be spread 

throughout the stand to enhance their establishment and dispersal.
18

CARE OF PARASITOIDS IF RELEASE IS DELAYED

The parasitoids should be released the day of arrival, however, if there is an unforeseen delay caused 

by late delivery or unexpected weather conditions, place the cardboard containers in a room that does 

not become overheated, unseal and open each box and internal plastic bag to determine the contents. 

Boxes containing:

• ash bolts with immature larval parasitoids can be held in closed bags and boxes.

• immature Oobius pupae on paper inside small plastic vials with screening will require you to 

open the box and the plastic bag and keep them where they will not become overheated.

• adult parasitoids inside clear plastic shipment cups, will require your care to survive beyond 

the day of arrival.

• To care for adult larval parasitoids (Tetrastichus and Spathius), open the box, remove and open 

the bags. Inside each bag will be a number of labeled cups containing small groups of live 

parasitoids. To maintain sufficient ambient moisture for the parasitoids, we recommend 

placing the rearing cups in a clear plastic storage tub with moistened paper toweling. Before 

placing the cups in the plastic tub, check each cup for the presence of honey. Honey provides 

the parasitoids with food and some moisture during shipping. If no honey is visible on the 

screening on the lids of the cups with Spathius or Tetrastichus, put two or three drops of 

honey on the screening and gently smear it. Open lids very carefully so adults do not escape. 

• Oobius adults shipped in clear plastic cups do not require additional honey and should not be 

opened. The cups should be held in open coolers in a well-lit room where they will not 

become overheated, as described above for the immature Oobius on paper in vials.

TRANSPORTING PARASITOIDS TO FIELD SITES

Carry the cups or infested logs inside the boxes when transporting parasitoids to the field for release. 

For delayed releases they do not need to be re-bagged for local transport. Care should be taken to keep 

the box out of direct sunlight or other potentially hot (e.g., a sealed vehicle) environments. The trunk of 

a vehicle will suffice, but an air-conditioned interior is even better, provided the vehicle will not be 

allowed to sit unattended in the sun for any period. Keep the box in the shade at all times because 

parasitoids are extremely sensitive to overheating when confined. Some people have stored parasitoids 
19

under their car to ensure shade, but this should be done with caution since a car may be extremely hot

near the engine. Keep the box closed except to remove the cups or logs with parasitoids for release. 

Carry the box carefully and avoid sudden movements. Parasitoids are extremely small and susceptible 

to drowning in droplets of water or honey if the cup is inadvertently shaken or dropped.

RELEASE OF PARASITOIDS

Adult Parasitoids. If possible, release the parasitoids in the morning or evening so they can move about 

in the environment before the onset of high afternoon temperatures. Carefully remove the snap-top lid 

with the tissue-paper liner or fabric liner when opening cups containing Oobius, Spathius or 

Tetrastichus adults. Place the cup and tissue next to the trunk of an appropriate ash tree. On warm 

sunny days, most of the parasitoids will crawl up to the lip of the cup onto the tree trunk or simply fly 

away. On cooler days, most of the parasitoids will remain in the cups. To dislodge these parasitoids, 

hold the cup upside down at a slight angle against the tree trunk and gently tap the cup against the tree, 

causing the parasitoids to jump or fly onto the tree trunk. You may find a small paintbrush useful for 

gently guiding any parasitoids that refuse to leave the cup but be very careful not to hurt the parasitoid 

in the process. Move the cups from tree to tree to ensure the number of each species is somewhat 

evenly distributed throughout the release site, this is especially important for Oobius as they do not fly 

as far as Spathuis or Tetrastichus.

Larval Parasitoid Pupae in Small Ash Bolts. The bolts containing parasitoid pupae will come with a 

pre-drilled hole through which you can insert a long wide head nail (4-5”) to pound into the tree trunk 

or use a shorter wide head nail and a zip-tie or wire to hang the log from the trunk. You can also use 

ziptie or wire to hang the bolts to branches of smaller trees. You will need a hammer, nails, and/or 

zipties or wire to hang the bolts in the field. Other options for hanging the bolts include tapping a 

nail into the top of the bolt and hanging the bolt from a short piece of wire, wrapped around a 

horizontal branch of the tree – this is particularly effective on large trees where trunk diameter makes it 

difficult to hang the bolt on the side of the trunk. Do not hang more than one bolt per tree if possible; 

the parasitoids will establish better if they are spread out. The bolts should remain in the field for at 

least 6 weeks to assure that all the parasitoids have emerged as adults. Remove the nails from the 

trees when you recover the logs because nails will harm sawmill equipment if the trees are 

harvested.

Oobius Pupae inside EAB Eggs on Paper in Oobinators. Hang one Oobinator per ash tree, and 

distribute them widely throughout release sites to encourage the spread and dispersal of Oobius. 
20

Choose trees that have evidence of fresh EAB attack such as current woodpecker feeding, live 

epicormic shoots along the trunk, or moderate canopy dieback (classes 2-3). Ash trees with flaky or 

coarse bark are preferred because they provide more oviposition sites for EAB to lay eggs; these are 

often the larger diametertrees in the stand. Each oobinator must be left on the trees for at least 6 weeks 

to allow all Oobius adults to emerge. Note: The oobinators in your Oobius shipment will have caps, 

do not forget to remove the caps before hanging them in the field.

ENTER RELEASE DATA

Release data provides valuable information on establishment of these parasitoids. Please record this 

data the day you conduct your releases, as you will quickly forget what the weather was like if it is not 

recorded. We ask that you enter release data using the MapBio app on your iPhone/iPad or online

at mapbiocontrol.org within 48 hours of release. Every time you release parasitoids, enter the 

following information into your MapBio app and synchronize/upload it, or these data can be recorded 

on datasheets in the field then entered directly online in mapbiocontrol.org:

• Release Date

• Release time

• Weather Conditions (Sunny, Partly Cloudy, Foggy, Light Rain, Moderate Rain, 

Heavy Rain, Thunderstorms)

• Wind Speed (Light, Moderate, Strong)

• Temperature (Degrees Fahrenheit)

• Number Female Oobius Released (when releasing as pupae this will be an 

estimate)

• Stage Oobius released (Adult, pupae, both)

• Number Female Spathius agrili Released (when releasing as pupae in ash logs 

this will be an estimate)

• Stage Spathius agrili Released (Adult, pupae both)

• Number Female Spathius galinae Released (when releasing as pupae in ash logs 

this will be an estimate)

• Stage Spathius galinae Released (Adult, pupae both)

• Number Female Tetrastichus Released (when releasing as pupae in ash logsthis will 
21

be an estimate)

• Stage Tetrastichus Released (Adult, pupae, both)

• Note

EVALUATING PARASITOID ESTABLISHMENT

Several methods have been developed that can successfully recover the four parasitoids released for 

EAB biocontrol. Unfortunately, none of the methods is consistently more effective than the others, and 

there are circumstances where parasitoids are recovered using one method but not others. Yellow pan 

traps are inexpensive and easy to sample, but they do not give any indication of the number of EAB 

attacked by parasitoids. Collecting EAB eggs and larvae from trees allow us to calculate percentage 

parasitism. However, these methods may require felling the tree for an adequate sample of EAB larvae 

from under the bark to detect larval parasitism. If resources permit, the best option is to use a variety of 

methods to ensure that if the parasitoids are present you can recover some.

To confirm establishment, sampling should be done at least one year after the final release at a given 

site. You only need to sample one release site per county, although more is always better. Below we 

describe the four parasitoid species and how their life cycle affects recovery sampling:

Tetrastichus planipennisi is a gregarious endoparasitoid (internal parasitoid) of EAB larvae, and 20 to 

>100 Tetrastichus larvae can develop inside their host. Tetrastichus may have three to four generations 

per year. An EAB larva parasitized by Tetrastichus may 1) look healthy; 2) appear lumpy like a 

“braided rope”; 3) be replaced by a mass of small grub-like larvae (white), pupae (color ranges white to 

bluish-black) and/or adults (dark metallic blue); or, 4) emerged from the EAB gallery, leaving only the 

head and tail of the EAB larva and small black spots in the gallery (the spots are waste excreted by 

each Tetrastichus larva before pupation is complete) (Appendix B). These parasitoids pupate in the 

EAB gallery and may be recovered by debarking ash trees. Adults may be recovered in yellow pan 

traps during spring, summer, and fall, although they are most abundant in late summer in northern 

areas.

Spathius agrili and Spathius galinae are gregarious ectoparasitoids (external parasitoids) of EAB 

larvae, and all life stages live on the outside of the host. Spathius eggs and small larva are difficult to 

see with the naked eye, but by late fall, most will be large larvae or will have spun silken cocoons that 

are fairly easy to see in the EAB galleries (Appendix B). Spathius agrili and several native species of 
22

Spathius require a period of chill to break diapause and emerge as adults, which are preferable for 

identification. For adult parasitoids to emerge from cocoons, we recommend felling trees for debarking 

after December (see the section below “Peeling Logs to Recover Larval Parasitoids”). If you would 

like to determine whether a recovered Spathius is one of the released species, you can remove a 

parasitoid larva from a cocoon, place it in 95% ethanol, and ship it to Juli Gould, 1398 West Truck 

Road, Buzzards Bay, MA 02542 for molecular identification. Like Tetrastichus, adults of S. agrili and

S. galinae can also be recovered in yellow pan traps.

Oobius agrili spends the winter in diapause inside EAB eggs, which are difficult to find sheltered 

between layers of bark and in bark crevices. EAB eggs are light brown or gold, whereas Oobiusparasitized eggs are often dark brown or black in color (Appendix B). Ash bark with EAB eggs can be 

scraped off trees in the field without injuring the tree, and the bark is dried and sifted to recover EAB 

eggs in the laboratory. See the DEBARKING section below, as well as an online PowerPoint

presentation with instructions and photographs at: 

https://www.mda.state.mn.us/sites/default/files/inline-files/barksifting2016_0.pdf Although Oobius 

adults are small, they can also be recovered in yellow pan traps.

NOTE: If you would like examples of parasitoid adults, larvae, pupae or cocoons to help with 

identification of parasitoids from the field, please contact the Rearing Facility for specimens

(EAB.Biocontrol.Program@usda.gov). If you have questions about parasitoid identification, recovery 

methods, where to purchase supplies and/or questions about how to construct, yellow pan traps, or 

emergence tubes, please email or call one of the authors.

TREE FELLING AND DEBARKING

Felling trees to determine parasitoid establishment can be done in the fall, winter, or early spring, at 

least one year after the final release at a given site. Select four trees near the release epicenter (vicinity 

of the original release trees) that are alive (based on bark peeling and confirmation of live phloem), 

show signs of fresh damage due to EAB (woodpecker holes, bark splits, epicormic shoots), and are less 

than 10-inches DBH. Give each tree a unique ID number, and record its DBH, location (GPS 

coordinates), and the date the tree was felled. 

DEBARKING
23

Before debarking the logs to recover larval parasitoids, use a draw knife to gently remove a thin 

layer of outer bark to collect EAB eggs.

Recovering the Egg Parasitoid Oobius from Outer Bark Samples:

Take bark samples from living, EAB-infested ash trees in the 

vicinity of the original release site in the field, or from trees felled 

for larval sampling. Fresh woodpecker feeding holes and/or live 

epicormics shoots are good evidence that the tree is infested with 

EAB. To sample trees in the field, mark off a vertical area of bark 

10 x 100 cm on the south, southwest, or west side on the lower 

trunk (about 1-m above ground) on at least 10 trees. To collect the 

bark samples, tightly wrap a piece of heavy plastic sheeting around 

the base of the tree with duct tape. Hold the edges of the sheeting 

up in the shape of an inverted cone (this method requires two people). Using a drawknife, shear 

off a thin layer of outer bark within the delineated area, and the bark debris will fall into the 

inverted plastic cone. Remove the duct tape and using the plastic sheeting, funnel the bark sample 

into a labelled large paper lunch bag, and return it to the laboratory.

Rearing O. agrili from bark: Oobius agrili overwinters inside EAB eggs as mature larvae. They 

emerge from eggs in the spring around 650 GDD50F. Bark samples can be reared in small rearing 

containers to collect adult O. agrili that may be overwintering in EAB eggs. These rearing containers 

can be constructed from 4” diameter cardboard poster tubes with tight fitting plastic plugs. Only a 

small number of parasitized EAB eggs will contain overwintering O. agrili that haven’t yet emerged, 

so a larger number of bark samples should be collected if you do not plan to sift the bark after rearing. 

If only rearing bark samples, we recommend taking 30 bark samples per site. If trees are limited, more 

than one bark sample may be taken from larger trees. If you choose not to rear the bark, then proceed to 

“Sifting O. agrili from bark.”

Supplies needed for rearing O. agrili from bark:

1. 4” diameter poster tubes cut 10-12” long and with tight fitting plastic plugs for each end.

2. Black spray paint designed to adhere to plastic.

3. 4.5 oz. clear specimen cup with lid. 

4. Small clear funnel. Large end 2” and funnel end 0.25” in diameter.

5. Hot glue gun.
24

6. 1.5” diameter hole saw bit for drill. Alternatively, a sharp knife and extreme care

On the left are the parts needed for construction of rearing tubes for rearing O. agrili from 

bark. On the right is a completed rearing tube for rearing O. agrili from bark.

Construction and collection from bark rearing tubes: The outer surface of plugs should be painted 

black with spray paint designed for application onto plastic. This will reduce light transmitted through 

the plugs and direct emerging adult parasitoids to 1.5–inch opening you will cut in one of the plugs. 

Cut a 1.5”-diameter hole in the center of one of the plugs. Next, cut a 1.5” diameter hole in the cap of a 

4.5-oz. specimen cup. Glue the larger end of the funnel to the bottom side of the specimen cup lid (side 

with threads) using hot glue. Then glue the top of the specimen cup lid to the outside surface of the 

poster tube plug, centering the holes that were drilled. Make sure that there are no tiny gaps between 

the plug surface and cap surface that would allow parasitoids to escape. The specimen cup can then be 

screwed onto the cap. Apply a streak of honey to the inside of the specimen cup to provide food for any 

emerging parasitoids. Check cups at least every other day for adult emergence. If parasitoids are 

present, you can squirt them with ethanol to prevent them from escaping and use a small brush to place 

them in vials with ethanol. Hold bark in rearing containers for at least 6 weeks at room temperature to 

allow all parasitoids to emerge. 

Sifting O. agrili from bark samples: Dry the sample at least one month at room temperature (if bark 

was already processed for rearing O. agrili it will already be dry), place small aliquots of bark in a No. 

14 covered soil sieve, and shake vigorously for several minutes to sieve EAB eggs, small insects and 

other small debris from the bark sample into a white ceramic baking pan. Using a dissecting 

microscope or magnifying glasses, sort and collect all EAB eggs and small adult parasitoids into a 
25

small Petri dish with friction-fitted lid (Fisher Scientific 50 X 9-mm dishes – catalog number 08-757-

105) labelled with state, site name, and date of collection using a fine-tip permanent marker. This 

method, including many photos of parasitized EAB eggs and look-alikes, is described at the following 

Minnesota Department of Agriculture webpage: https://www.mda.state.mn.us/sites/default/files/inlinefiles/barksifting2016.pdf. For confirmation or identification, ship the EAB eggs and parasitoids 

collected from bark sifting or reared from bark or logs to Juli Gould, UDSA-APHIS, 1398 West Truck 

Road, Buzzards Bay, MA 02542.

On the left a No. 14 covered soil sieve for sorting bark. On the right a white ceramic baking 

pan with sifted bark ready for viewing under a dissecting microscope. 

Bark samples to recover eggs can also be taken from ash trees felled for other recovery work. We 

suggest taking one bark sample per tree from flaky bark from a log cut from the lower two meters of 

each tree. You are more likely to find EAB eggs by sampling the part of the tree trunk that shows signs 

of recent EAB infestation and is still alive (i.e. the bark is still attached to the sapwood). From this part 

of the lower trunk mark, mark off a vertical area of bark 10 x 100 cm, debark this area of bark with a 

drawknife onto a piece of heavy plastic, and pour each bark sample into a large paper lunch bag, label, 

and rear or sift the bark samples as described above. Sample at least 10 trees per site. 

Peeling Logs to Recover Larval Parasitoids: 

The USDA has a short 5-minute video called “Debarking 

Ash Tree Logs to Look for Emerald Ash Borer” available on 

YouTube at: https://www.youtube.com/watch?v=sMV1r5lnvs&t=9s

Both species of larval parasitoid can be found in EAB 

galleries under the bark (for more information on the best 
26

time of year to sample trees, see the section above “Spathius agrili and Spathius galinae”). Logs are 

easiest to peel if debarked soon after felling, but if you need to store the ash logs in a cold chamber, 

consider sealing the ends (with Anchorseal® for example) to reduce moisture loss or keeping the logs in 

a barrel of water. If the bark is thick, remove the outer bark with a draw knife first. It is easiest to peel 

using a large 9-15” drawknife but if you find an EAB gallery you can more carefully remove the 

phloem in that area with a sharp chisel or small 5”drawknife. Phloem will easily separate from the 

outer sapwood when the ash logs are fairly fresh. Phloem and layers of outer sapwood will be harder to 

remove in areas where the tree is dead and dried out, but EAB and larval parasitoids can still be present 

in these areas if the tree died in the current year. Inspect all EAB galleries for signs of parasitized 

larvae, including empty galleries from which Tetrastichus has already emerged (see Appendix B for 

photos of parasitized EAB). Tetrastichus larvae remain inside the EAB larvae for at least a week before 

emerging from the EAB. If you have access to a laboratory you may find more parasitized larvae if 

you place 3rd, 4th, and J-larvae in a petri dish and dissect it. Many small eggs and parasitoid larvae can 

be seen swimming in the EAB haemolymph (See appendix B for helpful dissection photos). If EAB 

parasitism is suspected, carefully remove the EAB larva along with any parasitoid eggs, larvae and/or 

cocoons or pupae, and place them in a small Petri dish with a friction-fitting lid (Fisher Scientific 50 X 

9-mm dishes – catalog number 08-757-105 is a good choice). Using a fine-tipped permanent marker, 

label each Petri dish with the state, site, tree number, and date. Mail the specimens within one week to 

Juli Gould, 1398 West Truck Road, Buzzards Bay, MA 02542 for identification. For each tree, record 

the number of live EAB larvae, the number of solitary larvae or cocoons (probably Atanycolus – just 

count, do not ship), the number of broods of gregarious larvae (ship these for identification) and the 

number of broods of gregarious cocoons and pupae (ship these for identification). You do not have to 

count the number of parasitoids in each gallery. Enter these data into MapBioControl. The identifiers

will enter the final identification data into MapBioControl.

YELLOW PAN TRAPS

Many insects are attracted to the color yellow. Parasitoid recovery studies have shown that yellow pan 

traps (YPTs) are effective at trapping the introduced EAB parasitoids Tetrastichus planipennisi, S. 

agrili, S. galinae, and O. agrili. Other known EAB larval parasitoids (e.g. Spathius galinae, 

Atanycolus, native Spathius spp., Phasgonophora sulcata, Balcha indica) are also trapped, along with 

many other species of bees, wasps, flies, plant hoppers, and beetles. YPTs are simple and inexpensive 

to make.
27

Over the years we have found pan traps work really well in some situations and not so well in others. 

We still do not fully understand where they are most useful, but our general thoughts are as follows. A 

lot of the success of the traps seems to depend on where they are placed, and some trees are better for 

recovering parasitoids than other trees. Often, we find the same trees will catch parasitoids week after 

week, while nearby trees will recover nothing. We are not sure yet exactly what makes an ideal tree 

which is why we recommend more replicates. We have been investigating where the yellow pan traps 

are most successful and our thinking now is that they might work better in areas where there is ash 

along the edge of the forest (some of our most successful sites have been along greenways or bike 

paths or in street trees). We have shown consistently that trees with visible signs of fresh EAB and live 

phloem are the best for catching parasitoids (woodpecker feeding on the lower half of the tree is 

correlated with higher trap catches). This makes sense because parasitoids are going to look for hosts 

where hosts are present. Preliminary research shows that moderate to high canopy dieback (10-80%) is 

suitable for catching larval Tetrastichus planipennisi and likely also Spathius spp., and that moderate 

dieback (10-30%) is preferable for Oobius agrili. Trees with a large number of fresh woodpecker holes 

are preferable and canopy dieback is of secondary in importance to finding fresh woodpecker damage

and live phloem. Due to the dynamics of our forested areas it’s not always possible to find “ideal” 

trees, and a given tree will only be suitable for hanging yellow pan traps for a few years. Each year just 

do the best you can to find live but infested trees on which to hang the traps.

What will I need to make and deploy one YPT?

1. Two 12-oz yellow plastic bowls (color: yellow sunshine; can be purchased from Partycity.com)

2. One 8-inch (8 by 6 or 8 by 10) right-angled shelf-bracket

3. Three 1.25-inch long wood screws

4. Two small binder clips for securing the collection bowl to the holding bowl

5. A one-hole punch and a utility knife for altering the bowls

6. Fine-mesh screening (e.g. organza). If purchasing, try searching for no-see-um mesh. 

7. A hot glue gun. 

8. Weather-proof marking pen (e.g. Sharpie) or grease pencil (needed if bowls are wet)

9. Three 6-inch zip-ties (make sure they are thin and fit through the holes on the shelf bracket).

10. 20% solution of clear (not pink or green) propylene glycol (non-toxic antifreeze) diluted with water. 

You can search for Food or USP grade propylene glycol to find a supplier (also for sale at 
28

Amazon.com or Tractor Supply).

11. Rechargeable portable electric screw-driver with bit and extra battery pack

12. Unscented clear dish detergent

What will I need to collect the insect sample from the YPT?

1. One paint filter per pan trap per sample occasion (We use 190-micron fine mesh paint filters)

2. One Zipper or whirl pak plastic bag per pan trap per sample occasion (We use 6” by 9” bags).

3. Pencil (Not Pens) and paper

How are the YPTs mounted? Using the electric screwdriver, attach a shelf-bracket to the trunk of a 

living ash tree infested with EAB. Attach the bracket ~5 feet above the ground with the three wood 

screws. Make sure the top bracket is level or the bowl will not sit properly, you may have to leave the 

top screws partially unscrewed so that the bracket doesn’t tilt up too far up. 

What about those two yellow bowls? One yellow bowl is used as a 

“holding-bowl.” It is attached to the 8” side of the shelf-bracket 

with zip-ties threaded through the three shelf-bracket holes (on the 

horizontal surface). The zip ties should be threaded through pairs of 

holes punched into the holding bowl with a paper punch (0.5 to 1.0 

cm below the lip) and then through the hole in the shelf bracket. 

There are two holes in the shelf bracket next to the tree and one 

hole at the tip. Do not pull zip-ties too tightly to avoid distorting the 

holding-bowl. To provide drainage in the holding- bowl, cut a hole or two (~2.5-cm square) in the 

bottom with a utility knife.

The second yellow bowl or “collection-bowl” will hold the liquid that traps insects. It rests inside the 

holding-bowl. To prevent overflow from the collection-bowl after rainfall, punch at least 6 drainage 

holes just below the lip. Hot-glue a strip of fine-mesh screening (e.g. organza) over the drainage holes 

to prevent loss of specimens during overflow. After the bracket and holding-bowl are mounted on the 

tree, set the collection-bowl in the holding- bowl. Fill the collection-bowl ~3⁄4-full with the 20% 

propylene glycol solution (make sure that the propylene glycol is clear, not pink). Add one drop of 

unscented dish detergent to break the surface tension of the solution. This will allow inquisitive insects 

J. Hansen
29

to become entrapped in the liquid. You will need to empty the collection-bowl after three to seven days

to avoid possible loss of the sample due to weather, vandals, wildlife, decay, etc. We find that it is most 

convenient to collect samples once per week; adding fresh propylene glycol after collecting the first 

sample and continuing weekly samples. Secure the bowls together using two binder clips to prevent the 

bowl from getting blown out by the wind, which can happen as the liquid level lowers during drier 

weeks.

How many YPTs should I deploy and where? Deploy a total of 15 YPTs with one YPT per ash tree at 

your EAB biocontrol release site. If possible, select a variety of sizes of ash on which to place the 

bowls. Tetrastichus planipennisi cannot parasitize EAB in ash larger than 4 1⁄2 inches, EAB (and thus 

Oobius) are more likely to be found when the bark is flaky (as in larger trees), and Spathius species 

should be found on trees of varying sizes. The trees you select must show some symptoms of EAB 

infestation (e.g. fresh wood-pecker feeding, epicormic shoots) with crown class 3, or 4. Do not put the 

traps on dead or healthy ash trees (parasitoids will not be foraging on these trees). Distribute YPT’s on 

ash trees throughout the release areas and, if possible, place some traps at or near the release trees.

Label each YPT holding-bowl with a unique ID number using a weather-proof pen (e.g. Sharpie) or 

grease pencil if bowl is wet. On a data sheet, record the YPT-ID number, date, and initial of person 

collecting. Record the GPS coordinates – this will help you find the YPT later to recover the sample,

and it will let researchers know where the parasitoids were recovered.

When to deploy YPTs in the field? Deploy YPTs at EAB biocontrol release sites at least one year after 

the final parasitoid releases. Adult parasitoids fly during the spring, summer, and early fall, and the 

four introduced parasitoids have multiple generations per year, thus their populations are highest in 

mid-summer and early fall. However, the timing of possible captures in YPTs will depends on the 

climate in your area and the adult flight period of each species. If you have released Tetrastichus 

planipennisi and/or Spathius galinae and resources permit intensive sampling, we recommend 

deploying the YPT when 300 Growing Degree Days have been accumulated, then throughout the 

spring, summer, and early fall. This will require visiting sites weekly, collecting the samples, and 

replacing the liquid in the bowl for the next week of sampling. If resources do not permit such intensive 

sampling, then we recommend sampling once per month from 300 GDD50F through the end of 

September. In the south, where larval parasitoids are not expected to emerge during the spring, deploy 

the YPTs around 600 GDD50F for Oobius or when 3rd

-instar larvae become available in the mid-late 

summer.
30

How long do I leave YPTs in the field? The YPT samples should be collected three to seven days after 

new liquid has been placed in the trapping bowl. Samples left too long in the field will decay or dry up. 

Seven days is ideal because the longer the traps remain in the field, the more likely they will trap one of 

the target parasitoids. If you anticipate a heavy downpour, however, you might want to consider 

collecting the samples early. In limited cases cooperators have found that if they increased 

concentrations of Propylene glycol to 50%, samples can go up to 2 weeks before collecting. Care must 

be taken to test that this method will work at your site, if you find samples drying out or decaying from 

heat restart weekly collections. If using this method, bowls must be filled to the overfill hole to prevent 

it drying out. In addition, if you get a heavy rain event, empty traps soon after because it will both 

displace the solution from the bowl and dilute the remaining solution.

How is the insect sample collected from the YPT? After locating the YPT in the field, label your paint 

filter with the state, site, date (including year), and pan trap # in pencil (pen or marker may wash out). 

If there are many leaves in the sample, swish them in the liquid to dislodge any insects and discard 

them. Consider doing this with slugs as well as their slime can make the sample gummy and hard to 

process. Pour the contents of the trap (insects plus liquid) through a paint filter. A squirt bottle with 

water is recommended for dislodging insects from the bottom of the bowl or from leaves/slugs. The 

propylene glycol is not toxic and can be poured on the ground.

Fold over the open end of the paint filter and place each one separately into a zippered bag. If the filter 

is labelled in pencil you do not need to label the bag. If you cannot label the filter paper then label the 

bag instead with Sharpie. Consider bringing a cooler with ice packs while collecting samples if it is hot 

to help preserve insects before they are processed. A few hours in a hot car can cause insects to start to 

disintegrate and make it harder to ID samples later. Store samples in the refrigerator and process within 

one or two days. If processing is delayed, store the samples in the freezer.
31

Label the filter paper in pencil to avoid ink running and ruining the label. Also fold the filter 

paper over to avoid insects spilling out prior to processing.

What do I do with these samples? Because so many states are now doing recovery sampling, APHIS 

does not have the resources to sort potential parasitoids from YPT samples. Processing, or sorting, the 

YPT samples should be done locally, and suspect insect parasitoids that resemble the EAB parasitoids 

must be sent for positive identification because there are several native parasitoids in the genera 

Spathius, Tetrastichus, and Oobius that are easily mistaken for the EAB parasitoids. Positive 

identification of these parasitoids requires specialized taxonomic skills. To assist you in sorting the 

insects in the YPT samples, please contact the rearing facility (EAB.Biocontrol.Program@usda.gov) 

for examples of adult males and females of each EAB parasitoid species and refer to the instructions

below.

PROCESSING YELLOW PAN TRAP SAMPLES

Prior to processing or sorting the YPT samples, please contact the rearing facility for examples of adult 

males and females of each EAB parasitoid species. These will be helpful, along with the photos below, 

for you to find and identify possible EAB parasitoids in each YPT sample. It is especially important 

that you look at the example specimens using the same magnification you will use to sort the 
32

parasitoids from the YPT samples. Even though the parasitoids are quite small, you will be surprised at 

how large they look under magnification. Once you have prescreened your samples, send all suspect 

specimen samples by overnight shipping to Juli Gould, 1398 West Truck Road, Buzzards Bay, MA 

02542 for confirmation.

What do you need to sort through samples?

1. Dissecting microscope

2. Two pairs of fine forceps

3. A fine paint brush 0, 00, or 000 paint brush 

4. 95% Ethanol (for and preserving specimens)

5. 70% Ethanol (for checking the samples)

6. Small screw top vials (for specimens that need confirmation ID)

7. A small dropper to help add or remove specimens from the vials (optional)

8. A glass or plastic Petri dish to hold insect samples during the sorting process

Start by taking your samples out of the freezer if necessary. If they are very icy, give them some time to 

thaw. Try not to refreeze samples once thawed to help preserve the insects. If you have already thawed 

them you can leave the samples in the refrigerator for a day or two while you process them. Until you 

are very comfortable identifying the parasitoids it is a good idea to look through your reference 

parasitoids from the rearing facility right before processing your pan traps to familiarize yourself with 

the look and size of the insects you are searching for. While you may be looking at your reference 

parasitoids under a high magnification for details, also remember to look at your reference parasitoids

under the lowest magnification that you will be using as you look through your samples.

To start processing, open the zippered bag and record the location, date of the sample (including year), 

and pan trap number on your datasheet. Carefully unfold the filter paper, pull the filter apart at the 

seam, and dump the contents into your Petri dish. You may need to check the bag or outside of the 

filter if insects have slipped out of the filter. This may happen, especially if the filter was not properly 

folded over.
33

A filter paper spread out and ready for viewing under the microscope.

A sample that has been poured onto a glass Petri dish ready for viewing under the microscope.
34

A sample where 70% alcohol has been added to help separate the insects and where grid paper has 

been added to help provide reference points for sorting through the sample. 

Insects that have slipped out into the plastic bag. In this case view the bag under the microscope 

to check these insects as well.
35

Systematically sort through the insects caught on the filter under the microscope at the lowest 

magnification, looking for anything that looks similar to the EAB parasitoid species. You can use your 

paintbrush and/or forceps to help manipulate and check the sample. If you find something, look at it 

under a higher magnification and refer to the section below Photo Guide to Identifying Parasitoids in 

Yellow Pan Traps, as well as your reference specimens from the rearing facility. If you think it may 

be an EAB parasitoid, place it in a vial with 95% ethanol, include a paper label with site and date 

information written in pencil, and once you have accumulated a number of specimens for identification, 

pour most of the ethanol off each vial, and ship them overnight to Juli Gould, USDA-APHIS-PPQ, 

1398 West Truck Road, Buzzards Bay, MA 02542. 

Under lower magnification the insect near the forceps may be a specimen of interest. 

Readjusting to higher magnification makes it clear that the body shape does not match that of 

Oobius agrili.

Once you systematically check the filter paper, check the Petri dish containing all the larger

insects that you dumped out. Systematically go through the sample sweeping top to bottom and 

then gradually left to right until you look through the entire sample. We find it helpful to touch 

each insect and move it aside after determining that it is not a suspect EAB parasitoid. It may be 

possible for smaller insects to stick to a larger insect or to some of the dirt or leaves in your 

sample, so be sure to flip over insects and leaves and spread out dirt to make sure you are not 

missing any small insects. Be sure to check the legs and tarsi of larger insects as parasitoids often 
36

become tangled and trapped there. This commonly occurs for O. agrili. You may find in helpful 

to add 70% ethanol to help break up the sample so everything is not ‘stuck’ together. Some

processors have also suggested adding a grid to the bottom of your dish to help you sort through 

the sample systematically without missing anything. Finally, make sure that you have labelled 

and filled out your datasheet for that sample, toss away your insect and filter paper and move 

onto the next sample.

Place suspect parasitoids into glass or plastic screw-top vials with 95% alcohol. This alcohol 

must be poured off before shipping due to shipping restrictions, but alcohol will be added to the 

vials by the receiver. Send suspect insects to Juli Gould, USDA-APHIS-PPQ, 1398 West Truck 

Road, Buzzards Bay, MA 02542. 
37

Photo Guide to Identifying EAB Parasitoids in Yellow Pan Traps

Tetrastichus planipennisi (Eulophidae)

A eulophid wasp with red to dark red eyes and a 

tapered shape (females). Do not go by size alone as 

they can get very small if they are from a particularly 

large brood.

The female’s antennae have 6 segments: scape (1), pedicel (2), three funicles (3-5) and 1 

clava (6). The clava segment is more clubbed and robust (citation Yang et al. 2006).

D. Cappaert

Tetrastichus Female
38

The male’s antennae have 7 segments: scape (1), pedicel (2), 4 funicles (3-6) and 1 clava (7). The 

clava/last segment is thin and long. The antennae also are quite hairy, with the hairs having the 

look of eyelashes (much more evident in dead specimens than in these photos) (citation Yang et 

al. 2006).

The female’s abdomen is unique in that the final segment is very long. It is twice as long as the 

rest of the body (head plus thorax) and the abdomen is four times as long as it is wide.

Female 

Tetrastichus

Abdome Thora

Male 

Tetrastichus

Tetrastichus Male

Hairy ‘eyelashes’

Hairy ‘eyelashes’
39

Both sexes have two pairs of longitudinal grooves on the middle thoracic segment, a smooth 

thorax, and a dark femur.

Tetrastichus planipennisi Look-a-likes

Dark

femur

Setae too 

long

Antennae too short
40

Antennal hairs point 

out in all directions, too 

“spiny”

Femur 

clear

Hairs stick 

out in all 

directions
41

Oobius agrili (Encyrtidae)

Oobius agrili released for EAB biocontrol are all parthenogenic females, i.e. they do not need to mate 

and only produce daughters. Adults are very small (~1 mm long), have compact stout bodies with no 

waist, and a visible, short ovipositor. Their body color is black to dark brown with a blue-green sheen,

and reddish eyes.

Their antennae are distinctive. The segment (red arrow) before the clubbed clava is clear/yellow, 

while the other segments are darker (see photo of adult below). The antennae have 9 segments: 

scape (1), pedicel (2), six funicles (3-8) and the clava (9) is distinctly clubbed. The antennae are 

elbowed (or genticulate).

2

9 (Clava) 6 5

1

Zhang et al. 2005

D. Miller

~1 mm
42

Tarsus of O. agrili showing four tarsal segments. All known native species of Oobius have five 

tarsal segments. Note because Oobius are so small, you may not be able to see this feature clearly 

on your microscope. 

1

2

3

D. Miller

4

T.Murphy

Oobius 

agrili

Segment 

lighter than 

others
43

Spathius species (Braconidae)

The bodies of Spathius agrili and Spathius galinae are reddish brown expect for the abdomen, which is 

dark brown or black. Their wings have brown veins. The forewings tinged brown with clear banded 

areas. The hind wings are clear but still have brown veins. The antennae are very long, >26 segments 

with a total length that is 1.2 times the length of the body (without ovipositor). One very common 

native Spathius is Spathius floridanus. Spathius floridanus is a deep chocolate brown over the entire 

body and the back of the head has wrinkles (see photo below). The back of the head and cheeks of both 

S. agrili and S. galinae are totally smooth and wrinkle free (see photo).

On the left is the head of the native with lots of wrinkles, on the right is Spathius agrili which has 

a totally smooth head. Spathius galinae also has a smooth head, similar to Spathius agrili.

Spathius floridanus

Spathius agrili
44

Spathius agrili, like most Spathius species, has a distinct clear stripe across the middle of the 

forewing.

Spathius galinae looks very similar to S. agrili. It differs in that the wings look spotted rather 

than striped, the ovipositor is longer relative to the size of the body, and the base of the tibia of all 

legs is yellowish (see blue arrow in photo above).

Spathius agrili

Z. Yang et al. 2005

H Liu

J. Duan

Spathius galinae

Belokobylskij et al. 2012

M. Barrett

Spathius galinae

Spathius galinae
45

Spathius Look-a-likes

Head not spherical, 

femurs swollen, 

antennae short

Wings clear, body 

color more yellow 

than brown.

Antennae short, wing 

pattern is wrong, 

ovipositor sheath is 

short
46

Atanycolus sp.

Atanycolus is a large native parasitoid with a very distinct red or orange abdomen. In contrast, the 

head and thorax are jet black. The wings are dark grey.

ENTER RECOVERY DATA

It is critical that the EAB Biological Control Program have data on where EAB parasitoids are 

establishing. Once you have completed surveys to detect established parasitoids, enter the data directly 

at www.mapbiocontrol.org or using the MapBio iPhone/iPad app. Data on samples that were collected 

but in which no parasitoids were recovered are also critical. When you enter the mapbiocontrol.org web 

site, click on RECOVERY in the green banner at the top. Click the New button to enter new data. You 

will be asked to enter the following data:

• Trap ID: The Trap ID number in mapbiocontrol is a holdover from a previous protocol. 

We do not expect you to enter each trap separately, rather enter each site and collection date 

H. Lui
47

once and enter the number of traps (usually 15). However, the Trap ID is a required field. This 

data is critical because the scientists who identify collected parasitoids need to match the 

identified insects to the sites and locations where the parasitoids were recovered. We 

recommend that you enter a code for the release site as a place holder. If you are interested in 

knowing which traps collect parasitoids, make sure that the label in the vial includes the trap

number.

• Latitude (dd.ddddd)

• Longitude (dd.dddd)

• Site ID Once you type in the Latitude and Longitude of your sample, the database will 

select some nearby sites from which to choose. Select the appropriate site. If you happened 

to find parasitoids not connected with any particular release or control site, simply select 

NO Site.

• State

• Date Sample Collected

• Sample Method (Yellow Pan Trap, Tree Debarking, Logs in Tubes, Bark in Tubes, 

Sentinel Eggs, Sentinel Larvae, Egg Collection, Other)

• Number of Samples 

• Possible EAB Parasitoids Recovered? Yes or No

If you did recover some possible EAB parasitoids, record the date they were shipped for identification,

and the person they were shipped to. The data on the number of released parasitoids recovered will be 

entered into the database by the identifiers.

Forest Type

On mapbiocontrol.org in the Release section, there is a tab for Forest Type. Collecting Forest Type data 

is not required, but if you have the time and resources it will greatly assist researchers in determining 

which types of forest compositions are more likely to promote establishment of EAB parasitoids.
48

Ash Health Assessment

On mapbiocontrol.org in the Release section, there is a tab for Ash Health Assessment. Collecting Ash 

Health Assessment data is not required, but if you have the time and resources it will greatly assist 

researchers in determining the trajectory of ash mortality and how it correlates with the establishment 

of EAB parasitoids.

Mention of companies or commercial products does not imply recommendation or endorsement 

by the U.S. Department of Agriculture over others not mentioned. USDA neither guarantees nor 

warrants the standard of any product mentioned. Product names are mentioned solely to report 

factually on available data and to provide specific information. 
Appendix A – EAB Life Stages and Damage 

A-1

EAB Life-Stages

EAB eggs (newly laid egg is white maturing to an amber color; clutches of eggs laid between bark 

flakes; single eggs in bark crevices)

EAB larvae (1-4 indicates the four instars)

D. Miller

T. Petrice

D. Miller L. Bauer

L. Bauer D. Miller
Appendix A – EAB Life Stages and Damage 

A-2

EAB larva (head is to the left; 

note urogomphi at the posterior end of larva)

EAB J-shaped larvae in pupal chamber in outer sapwood (left); pre-pupa (center); pupa (right); 

stages of maturing pupae (bottom left)

D. Miller

J. Gould D. Miller

D. Miller

L. Bauer

D. Cappaert

D. Miller

EAB Adults
Appendix A – EAB Life Stages and Damage 

A-3

Larval Galleries 

External signs of EAB overwintering chamber under the bark. The photo on the left shows the EAB 

gallery filled with light colored frass and the photo on the right shows the exit portals of three pupal 

chambers, each with 2 holes filled with frass.

J. Gould J. Gould

L. Bauer J. Gould J. Gould
Appendix A – EAB Life Stages and Damage 

A-4

Signs of EAB infestation

Thinning Ash Crowns

Epicormic shoots in winter (left) and summer (right)

L. Bauer J. Gould

J. Gould
Appendix A – EAB Life Stages and Damage 

A-5

Bark Split with Larval Galleries Beneath the Bark (note callusing around old gallery)

Woodpecker Feeding on EAB in lower ash trunk and midcrown

USDA APHIS PPQ EAB

USDA APHIS PPQ EAB

L. Bauer

USDA APHIS PPQ EAB
Appendix A – EAB Life Stages and Damage 

A-6

Adults emerging from D-shaped exit holes

D-shaped exit holes

Additional photos and specific morphological and physiological information can be found in the EAB Program 

Manual at:

http://www.aphis.usda.gov/import_export/plants/manuals/domestic/downloads/emerald_ash_ borer_manual.pdf

USDA APHIS PPQ EAB USDA APHIS PPQ EAB

D. Miller
Appendix B - Parasitoid Life Stages

B-7

Life stages of EAB Parasitoids

Spathius agrili

S. agrili lays eggs on the surface of EAB larvae.

Larvae of S. agrili feed externally on an EAB larva.

Silken cocoons of S. agrili in the host gallery contain mature larvae or pupae.

Z-q Yang

Z-q Yang

H. Liu J. Gould
Appendix B - Parasitoid Life Stages

B-8

Female S. agrili lay eggs through ash bark onto an EAB larva.

Spathius galinae

Spathius galinae larvae and cocoons

Spathius galinae adult female

Z-q Yang

M. Barrett

M. Barrett
Appendix B - Parasitoid Life Stages

B-9

Tetrastichus planipennisi

Immature T. planipennisi larvae inside EAB

Mature T. planipennisi larvae inside an EAB larva

T. planipennisi larvae emerge from host remains and pupate in the gallery.

D. Miller

J. Lelito

J. Lelito
Appendix B - Parasitoid Life Stages

B-10

T. planipennisi larvae develop asynchronously, and larvae and pupae are often found 

together inside one EAB gallery.

T. planipennisi meconia (waste) leave black spots in the empty EAB gallery after adult 

emergence is complete.

T. planipennisi female lays eggs in an EAB larva through ash tree bark.

L. Bauer

X-Y Wang

H. Liu
Appendix B - Parasitoid Life Stages

B-11

Dissected EAB with visible T. planipennisi larvae under the scope.

EAB larva ready for dissection under the scope, T. planipennisi larvae are visible swimming with the 

EAB haemolymph. 

Dissected EAB larvae 

may have bits and 

particles that look like a 

larvae or egg but unless 

you see several distinctive 

eggs or larvae it is not T. 

planipennisi

T. Murphy 

T. Murphy 
Appendix B - Parasitoid Life Stages

B-12

A native parasitoid, Phasgonophora sulcata, dissected from an EAB larva. This parasitoid is a solitary 

endoparasitoid, you’ll see only one larva (rarely two but one is usually dead). The larva is usually 

found near the tail end of the EAB. Phasgonophora sulcata has a distinctive head end and tail end, 

unlike a T. planipennisi larva.

Oobius agrili

EAB eggs often turn dark brown when parasitized by O. agrili; unparasitized, healthy eggs 

remain amber in color (center egg).

D. Miller

R. Crandall

R. Crandall
Appendix B - Parasitoid Life Stages

B-13

Adult O. agrili chew a circular hole through the EAB egg shell and emerge.

O. agrili female parasitize EAB eggs laid on ash bark

H. Liu

D. Miller
Appendix C – Crown Condition of Ash Trees 

C-1

Crown-class condition for ash trees infested with EAB (Smith, A. 2006. Effects of community structure on forest susceptibility and 

response to the emerald ash borer invasion of the Huron River watershed in southeast Michigan. M.S. Thesis, The Ohio State University)

1 2 3 4 5
Appendix D – Helpful Links 

D-1

mapBioControl (to enter release and recovery data):

www.mapbiocontrol.org

Growing Degree Days:

http://uspest.org/US/

General EAB Information

EAB Program Manual:

http://www.aphis.usda.gov/import_export/plants/manuals/domestic/downloads/emerald_ash_

borer_manual.pdf

APHIS Emerald Ash Borer Home Page:

https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-diseaseprograms/pests-and-diseases/emerald-ash-borer

http://www.emeraldashborer.info/

https://www.aphis.usda.gov/aphis/resources/pests-diseases/hungry-pests/the-threat/emeraldash-borer/emerald-ash-borer-beetle

EAB Biological Control:

http://nrs.fs.fed.us/disturbance/invasive_species/eab/control_management/biological_control/
Appendix E – Releasing Parasitoids for Optimal Establishment 

E-1

Spathius agrili is expected to establish in areas with EAB undergoes a one-year life cycle, while T. planipennisi and S. galinae are expected to 

establish in areas where EAB has a two-year life cycle. We collected data on overwintering of EAB at 69 sites in 21 states to find the range of 

one-year and two-year life cycle of EAB in the US and modelled the proportion of EAB expected to be in a two-year life cycle. We matched this 

model with data on T. planipennisi establishment to help guide where we will release T. planipennisi, S. galinae and S. agrili. 

• Tetrastichus planipennisi will be preferentially released at locations that accumulate fewer than 3,500 GDD50F between January 1 and 

September 30.

• If your site accumulates > 3,500 GDD 50F in the summer and you would still like to release T. planipennisi, confirm that you have 3-4thinstar EAB larvae in late winter or early spring before scheduling T. planipennisi releases. 

• We rarely see establishment of T. planipennisi at sites where >3,975 GDD 50F accumulate in the summer, and we do not recommend 

releasing this species in these locations.

• We will follow the same guidelines for releasing Spathius galinae.

• Spathius agrili will only be released at sites that accumulate > 3,500 GDD 50F. It has not established in areas with fewer GDD.

Table 1: Maximum threshold for accumulated growing degree days for Jan. 1 – Sept. 30 (base 50 ̊F) to achieve a given predicted probability of 

EAB overwintering as larvae. For each predicted probability of EAB larvae we also show the percentage of sites where Tetrastichus 

planipennisi was released and establishment occurred.

Modelled percentage EAB 

overwintering as larvae

Growing Degree Day 

Threshold

Percentage of sites samples with 

T. planipennisi establishment 

51-80% 2,985 92%

26-50% 3,500 78%

11-25% 3,975 50%

0-10% - 23%
Appendix E – Releasing Parasitoids for Optimal Establishment 

E-2

Figure 1: 

Predicted proportion of EAB that spend the winter as larvae instar 1-4, not as J-larvae. Locations where Tetrastichus planipennisi has been 

collected two or more years following the final release are indicated in green. Locations where samples were collected but T. planipennisi was 

not recovered are marked in red.