One or two generations occur per year. Winter is spent as a prepupa in a cocoon in the soil. Pupation occurs in the spring time, and adults emerge in May. Eggs are laid and larvae occur from April-May (1st generation) and again in mid-July to mid-September (2nd generation). Larvae have a black head capsule and are generally yellow in color with black markings and may reach up to an inch in length when fully grown. Larvae sit in an S-posture (rear-end out) when alarmed or not feeding. If there is a second generation, adults may emerge again from mid-July to mid-September. Adults are approximately 1/2 inch in length and look like black wasps.
Foliage of birches, primarily gray birch, but also black, yellow, and paper birches is consumed. Small trees may be defoliated by these caterpillars that feed in groups, particularly around leaf margins.
Look for leaves eaten from the edge working inward. Search the margins of those leaves for sawfly caterpillars. Remember, sawfly caterpillars typically have 6 or more prolegs.
When found, drop caterpillars into a can of soapy water or prune out and destroy the branch section they are feeding on. This may be particularly effective on smaller trees where isolated populations can be mechanically destroyed without chemical intervention. Reportedly, numbers of this species rarely reach levels where chemical intervention is necessary.
None reported specific to this species, but other sawflies in this same genus have reportedly been parasitized by Compsilura concinnata and other parasitoids.
Acephate (NL)
Azadirachtin (larva only) (NL)
Bifenthrin+imidacloprid (L)
Carbaryl (L)
Chlorpyrifos (N)
Cyfluthrin (larva only) (NL)
Deltamethrin (larva only) (L)
Dinotefuran (larva only) (NL)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (larva only) (L)
Imidacloprid (larva only) (L)
Insecticidal soap (larva only) (NL)
Lambda-cyhalothrin (L)
Pyrethrin+sulfur (larva only) (NL)
Spinetoram+sulfoxaflor (larva only) (N)
Spinosad (larva only) (NL)
To entomologists, the term caterpillar refers to the immature or larval life stage of the Lepidoptera - butterflies and moths. However, the public and some entomologists included sometimes use this term interchangeably to refer to the immature or larval life stage of certain Hymenoptera - in particular, sawflies.
This can cause confusion when selecting management options for pests collectively referred to as caterpillars. The larvae discussed here will mature into an adult sawfly. This means that the active ingredient Bacillus thuringiensis Kurstaki (Btk) will not be effective at managing this insect. Btk will only kill the caterpillars of moth (or butterfly) pest insects. It will not kill sawfly larvae.
Sawfly larvae can be distinguished from moth or butterfly caterpillars by the presence of or absence of 6 or more prolegs. Some sawfly species will have 6 or more pairs of fleshy abdominal prolegs, whereas some sawfly larvae will have 0 pairs of fleshy abdominal prolegs. Caterpillars that mature into butterflies or moths will have 5 or fewer pairs of fleshy abdominal prolegs. Prolegs are soft, and found behind the hardened 3 pairs of thoracic legs on the insect. In butterfly or moth caterpillars, the prolegs will also have tiny hooks or crochets on the very bottom.
Active ingredients that may be applied systemically include: acephate (injection), azadirachtin (injection, soil drench) dinotefuran (soil drench), and imidacloprid (soil drench).
When used in nursery setting, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
