Questions and Answers: 

USDA’s Emerald Ash Borer Biocontrol Program

Q. What is biocontrol?

A. Biological control (biocontrol) is the reduction of 

pest populations through the use of natural enemies 

such as parasitoids (stingless wasps), predators, 

pathogens, antagonists (to control plant diseases), 

or competitors. It is a practical option to suppress 

pest populations and an environmentally sound 

method of pest control. 

Q. What is biological control in relation to USDA’s 

Emerald Ash Borer (EAB) Program? 

A. Two U.S. Department of Agriculture (USDA) 

agencies—the Animal and Plant Health Inspection 

Service (APHIS) and the Forest Service—initiated a 

biological control effort shortly after the EAB beetle 

was detected in Michigan in 2002. USDA research 

in the beetle’s native range of China identified three 

potential biological control agents (stingless wasps) 

for EAB—Spathius agrili, Tetrastichus planipennisi, 

and Oobius agrili.

Following host range testing, USDA prepared an 

environmental assessment that outlined the risks and 

benefits of releasing the stingless wasps. The wasps 

specifically hunted EAB to an acceptable degree 

and were not expected to attack insect species other 

than EAB, except for incidental attacks on other 

wood-boring (Agrilus) species. USDA then prepared 

a “finding of no significant impact,” a decision 

document explaining the reasons for this conclusion. 

With this finding and with approval from the State of 

Michigan, USDA released the wasps in July 2007. 

Limited releases also took place in 2008.

Q. What do you mean by stingless wasps? 

A. The EAB biocontrol agents are very tiny wasps—

the largest one is about the size of a typical mosquito. 

Female wasps use an organ that looks like a stinger 

(called an ovipositor) to lay their eggs. Despite their 

appearance, the wasps cannot sting, so they are 

referred to as stingless. 

To see photos of the stingless wasps and other 

EAB-related images, please visit our Web site at 

www.aphis.usda.gov/wps/portal/aphis/ourfocus/

planthealth. Click on “Pests and Diseases,” then 

“Pest and Disease Programs,” then “Emerald Ash 

Borer,” and “Image Gallery.” 

Q. How many species of wasps have been released?

A. APHIS has reared three stingless wasp species 

and released them in EAB-infested areas of the 

United States. Two of the wasps attack EAB larvae, 

and one targets EAB eggs. 

• Spathius agrili has a long, egg-laying organ 

(ovipositor) that enables it to attack larvae in 

ash trees of various sizes. Spathius targets EAB 

larvae by drilling through the bark and laying 

up to 20 eggs on its host. The hatching wasp 

larvae feed and develop on the EAB larva, 

resulting in the EAB larva’s death.

• Tetrastichus planipennisi also attacks EAB 

larvae. The life cycle of Tetrastichus is similar 

to that of Spathius; however, the female lays 

eggs inside EAB larvae where the wasp larvae 

grow, eventually killing their host. Because of its 

shorter ovipositor, Tetrastichus targets larvae in 

ash trees with a diameter of 5 inches or less.

• Oobius agrili is the smallest of the wasps and 

targets EAB eggs. When Oobius locates an EAB 

egg in the bark crevices, the wasp injects its 

own egg inside the host egg, where it will hatch, 

grow, and kill the EAB larva before the EAB 

larva can emerge from the egg.

ANIMAL AND PLANT HEALTH INSPECTION SERVICE SEPTEMBER 2014 

PLANT PROTECTION AND QUARANTINE
Q. Will the wasps bother people or pets?

A. No. The wasps target the EAB eggs and larvae 

and are not attracted to people or pets.

Q. Is it safe to release these non-native insects? 

A. Yes. Before USDA released the stingless wasps, 

testing in China and the United States revealed that 

the wasps prefer EAB over other insect species. 

Also, in USDA’s environmental assessment, no 

critical issues were raised during the 60-day public 

comment period, which supported our finding of no 

significant impact. To read these documents and 

public comments go to www.regulations.gov/#!docket

Detail;D=APHIS-2007-0060.

Q. Who determines whether to release stingless 

wasps?

A. USDA and State officials, along with national 

EAB Program management, collectively determine 

release sites for EAB biocontrol. State cooperators 

secure permits and agree to follow standardized 

release and monitoring protocols. Cooperators 

also agree to monitor release sites for parasitoid 

establishment following the protocol in the 

“EAB Biological Control Release and Recovery 

Guidelines.” 

Q. When and where were the wasps released in 

the United States?

A. Stingless wasps were first released in 2007 in 

Michigan. Since that time, one or more species 

of the wasps have been released in 19 States: 

Colorado, Connecticut, Illinois, Indiana, Kentucky, 

Maryland, Massachusetts, Michigan, Minnesota, 

Missouri, New Hampshire, New York, North 

Carolina, Ohio, Pennsylvania, Tennessee, Virginia, 

West Virginia, and Wisconsin. 

Q. How effective are the wasps at reducing 

EAB populations?

A. Although it is premature to talk about the wasps’ 

effect on EAB populations, a recently published 

study reported that stingless wasp populations 

in Michigan are increasing and spreading into 

adjacent areas. In addition, cooperators in 10 

States (Indiana, Illinois, Maryland, Michigan, 

Minnesota, New York, Ohio, Pennsylvania, 

Tennessee, and Wisconsin) have successfully 

recovered the offspring from one or more wasp 

species. We anticipate more evidence of progress 

as release sites are continually monitored.

Q. Will biological control eventually eradicate EAB?

A. Stingless wasps will not eradicate EAB. 

However, they can be used in an integrated pest 

management plan to help control the pest and 

benefit our urban, suburban, and rural landscapes. 

Continued scientific advances in the fields of forest 

health, pest management, and entomology offer 

promise that more effective treatments and tools 

will eventually be available to fight EAB. 

Q. Who is involved in the EAB biocontrol program?

A. APHIS works with USDA’s Agricultural Research 

Service, Forest Service, and various State partners 

to maximize the efficiency and effectiveness of 

EAB biocontrol. 

Q. Can the public purchase the stingless wasps

used in EAB biocontrol? 

A. No. The stingless wasps are difficult to produce, 

which limits their availability. The goal of the EAB 

biocontrol program is to provide stingless wasps to 

States that have EAB infestations. 

Q. Is it true that there are native insects in the

United States that attack EAB?

A. Yes. Some natural enemies (parasitoids and 

predators) of the EAB have been detected in the 

United States. A native stingless wasp, Atanycolus, 

was found attacking EAB larvae at a number of 

sites in Michigan. Also, the predator wasp Cerceris 

fumipennis is used as a detection tool in some 

States. Unfortunately, these native enemies do not 

appear to provide a significant level of pest control 

for EAB populations. 

Q. Where can I find more information on EAB and 

the biocontrol program?

A. To learn more, go to our Web site at www.aphis.

usda.gov/wps/portal/aphis/ourfocus/planthealth. 

Click on “Pests and Diseases,” then “Pest and 

Disease Programs,” and “Emerald Ash Borer.” 

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opportunity provider 

APHIS 81-35-023 and employer.