Cover Photos: Top - H. crocea larvae 

Bottom Left - A M. pulveratum larva 

Bottom right - An E. ovata larva

Alder-feeding Sawflies of Alaska

In recent years, Alaskan alders have been 

increasingly assaulted by a variety of insects, 

pathogens and abiotic agents. Recent 

examples are: vast areas of generalized 

foliage browning in interior, south-central, 

and southwestern Alaska; a six year 

outbreak of the generalist, native, hardwood 

defoliator, Sunira verberata in Katmai 

National Park; extensive defoliation by the 

invasive alder woolly sawfly, Eriocampa 

ovata, in the Anchorage area beginning in 

the mid-1990’s; a wide variety of canker 

fungi, most commonly Valsa melanodiscus, 

causing premature leaf death, stem dieback, 

stem death, and whole clump mortality 

at local and landscape levels throughout 

Alaska; and finally, severe defoliation by a 

new, exotic sawfly, Monsoma pulveratum, 

primarily in south-central Alaska. Further, 

more than one of these agents are frequently 

found acting in concert—several species of 

defoliators for example, or insect/pathogen 

interactions.

The three primary, alder-feeding sawflies 

in Alaska are: Eriocampa ovata, the alder 

woolly sawfly; Hemichroa crocea, the striped 

alder sawfly; and Monsoma pulveratum, 

the European green alder sawfly. Both 

the green alder and alder woolly sawflies 

are nonnative insects, while the striped 

alder sawfly is a native, circumpolar 

sawfly. All three are in the same insect 

order, Hymenoptera (bees, wasps, ants, 

and sawflies), and the same insect family, 

Tenthredinidae. These sawflies share a 

number of characteristics: all insert a 

single egg through the leaf cuticle into 

the leaf tissue using a strong, somewhat 

‘saw-like’ ovipositor; larvae are all external 

leaf feeders; all pupate in the ground in 

an excavated chamber where they spin 

a cocoon or line the chamber with silk; 

and finally, all exhibit a strong preference 

for thin-leaf alder (Alnus incana subsp. 

tenuifolia) as a primary host. The adults are 

all small, compact insects, and even though 

they are wasps, to the casual observer they 

more often resemble flies. Although they are 

included in the same insect family as wasps 

and bees, they are neither venomous, nor 

capable of stinging. 

 Life History

The green alder sawfly is the first of the 

three sawflies to emerge in the spring. 

Egg-laying is in progress in mid-May, at 

James Kruse (Entomologist), Ken Zogas, Nicholas Lisuzzo and 

Steve Swenson (Biological Science Technicians), USDA Forest 

Service, Alaska Region, State and Private Forestry.

Additional information on this insect can be obtained from 

your local Alaska Cooperative Extension office, Alaska State 

Forestry office, or from: 

Forest Health Protection

State and Private Forestry

USDA Forest Service

11305 Glacier Highway

Juneau, Alaska 99801-8626

Phone: (907) 586-8883 

Forest Health Protection

State and Private Forestry 

USDA Forest Service

161 East 1st Avenue, Door 8

Anchorage, AK 99501 

Phone: (907) 743-9449 

Forest Health Protection

State and Private Forestry 

USDA Forest Service

3700 Airport Way 

Fairbanks, Alaska 99709 

Phone: (907) 374-3758 

http://www.fs.fed.us/r10/spf/fhp

Alder-feeding 

Sawflies of Alaska

The U.S. Department of Agriculture (USDA) prohibits 

discrimination in all its programs and activities on the basis 

of race, color, national origin, sex, religion, age, disability, 

political beliefs, sexual orientation, or marital or family status. 

(Not all prohibited bases apply to all programs.) Persons with 

disabilities who require alternative means for communication 

of program information (Braille, large print, audiotape, etc.) 

should contact USDA’s TARGET Center at (202) 720-2600 (voice 

and TDD).

To file a complaint of discrimination, write USDA, Director, 

Office of Civil Rights, Room 326-W, Whitten Building, 1400 

Independence Avenue, SW, Washington, DC 20250-9410, 

or call (202) 720-5964 (voice and TDD). USDA is an equal 

opportunity provider and employer.

United States

Department of

Agriculture

Prepared by

Forest Service

Alaska Region

Leaflet

R10-TP-154 

October 2012 Figure 1. Extensive alder defoliation and 

dieback along the Susitna River, Alaska.
approximately 15°C, when the alder leaves 

are just beginning to flush. Both alder woolly 

and striped alder sawfly adults emerge from 

mid to late June. Egg-laying commences 

immediately and continues for several 

weeks as new adults emerge. Green alder 

sawfly egg deposition differs markedly from 

the two other sawfly species. Egg deposition 

for green alder sawflies is on the upper leaf 

surface, alder woolly sawflies egg deposition 

is on the underside of the leaf along and 

into the midrib, and striped alder sawflies 

egg deposition is along the leaf petiole. 

Embryonic sawfly development for all three 

species is 1-2 weeks. Upon hatching, green 

alder sawfly larvae migrate to the lower 

leaf surface. All three species feed openly 

on the leaves, consuming (in most cases) all 

the soft leaf tissue, leaving behind only the 

leaf veins and midrib. Striped alder sawfly 

larvae feed gregariously, while the alder 

woolly and green alder sawflies feed singly. 

However, in high larval density situations, it 

is not uncommon to find five or more green 

alder sawfly larvae per leaf. At times, only 

one species might be found on an individual 

alder. It is possible to have two or even all 

three species feeding on the same plant, or 

even on the same leaf.

Appearances differ markedly among the 

larvae. Green alder sawfly larvae are creamycolored to very pale green upon hatching. 

As they grow and develop, they change to 

a vibrant bluish-green. Full grown larvae 

can exceed 18 mm in length. Alder woolly 

sawfly larvae secrete a white, waxy, hairlike covering on their bodies. As they grow, 

this covering becomes denser. In their last 

instar (stage of larval development), the 

covering is shed, exposing a very pale green 

body. The larvae of striped alder sawfly are 

yellowish- to greenish- brown with two 

black lateral stripes on either side of their 

body. They are quite robust, though slightly 

shorter in length at full development than 

alder woolly or green alder sawflies. When 

larval development is complete, the woolly 

alder and striped alder sawflies drop to the 

ground and burrow into the soil beneath 

the leaf litter. There, they excavate a small 

chamber 1-4.5 cm beneath the soil surface. 

The larvae then enter a pre-pupal state and 

remain in this condition throughout the 

winter. In spring, when the ground begins to 

warm and reach the threshold temperature 

for each species to continue development, 

the pre-pupae change to pupae, and after 

some time, they emerge as adults. By 

contrast, the green alder sawfly typically 

burrows into woody material, and spends 

the winter in stumps, broken branches and 

down logs. This behavior is believed to be 

unique to this genus of sawfly, and may 

account for their early emergence in the 

spring.

Detection and Damage

The damage to the host alders due to sawfly 

feeding is quite obvious. Early in the season, 

as active feeding begins, numerous small 

holes appear in the leaves as the small 

larvae feed. This results in a characteristic 

“shotgun” appearance. In time, these small 

feeding voids coalesce into larger holes. 

Ultimately, the larvae consume all the soft 

tissue between the leaf veins leaving behind 

only the stouter veins and leaf midrib. The 

shrub takes on a thin, brownish appearance 

easily seen from the ground or aerially. 

Alder, like most hardwood tree species, 

is able to withstand several seasons of 

severe defoliation suffering nothing more 

than growth loss and possibly branch 

dieback. With the case of alder however, 

severe defoliation can reduce its nitrogen 

contribution to the soil by more than 70% 

annually. Alder mortality has been observed, 

in other defoliator outbreaks, after 5 or more 

consecutive seasons of severe defoliation.

Control Options

Since thin-leaf alder is primarily a riparian 

species and an important component 

of many salmon spawning streams, 

implementation of sawfly control measures 

would be difficult. Some insecticides have 

deleterious effects on aquatic insects as well 

as the terrestrial insects they specifically 

 CAUTION: Pesticides can be injurious to humans, 

domestic animals, desirable plants, and fish or other 

wildlife—if they are not handled or applied properly. 

Use all pesticides selectively and carefully. Since 

approved uses of a pesticide may change frequently, 

it is important to check the label for current approved 

and legal use. Follow recommended practices for the 

disposal of surplus pesticides and pesticide containers. 

Mention of a pesticide in this publication does not 

constitute a recommendation for use by the USDA, 

nor does it imply registration of a product under 

Federal Insecticide, Fungicide, and Rodenticide Act, as 

amended. Mention of a proprietary product does not 

constitute an endorsement by the USDA. 

target. Many of the infested alders lie within 

an area normally excluded from operational 

insecticide spray programs because of its 

ecological sensitivity.

Homeowners do not normally encounter 

problems with these insects. If an individual 

is concerned about a small group of infested 

alders on their property, effective control 

can be achieved either through hand-picking 

of the larvae from the leaves or treatment 

with a strong jet of water. Repeating these 

activities several times throughout the 

summer may be required.

Figure 2. a- H. crocea egg sites.

b- M. pulveratum egg sites. c- E. ovata egg 

sites. d- An alder leaf after larval feeding.

a

d

b

c

Figure 3. a. An adult M. pulveratum 

b. Overwintering sites for M. pulveratum larvae

a b