One generation occurs per year. The larvae of the dogwood sawfly overwinter in decaying wood and occasionally compromised structural timber. An overwintering "cell" is created in this soft wood. Pupation occurs in the springtime and adults can take a lengthy time to emerge, roughly between late May and July. 100+ eggs are laid in groups on the underside of leaves. Eggs hatch and the larvae feed gregariously, initially skeletonizing leaves. As the caterpillars grow in size, they are capable of eating the entire leaf with the exception of the midvein. Larval appearance varies greatly throughout instars, so much so that one might mistake them for multiple species. Early instars are translucent and yellow, but as the caterpillars grow they develop black spots (over yellow) and become covered in a white powder-like material. Larvae and their shed skins may resemble bird droppings. Full grown larvae begin to wander in search of a suitable overwintering location. Rotting wood lying on the ground is preferred for this.
Foliage of dogwood, esp. gray dogwood (Cornus racemosa). Skeletonizes leaves at first, then eats all but the midvein.
Look for eggs laid in groups, particularly near the leaf veins of gray dogwood. Also scout for skeletonization caused by newly hatched caterpillars prior to heavier feeding. These sawfly caterpillars can cause a great amount of defoliation on their host, given their group-feeding behaviors.
Remove groups of sawflies feeding together and drop into soapy water if necessary. Older caterpillars may be difficult to manage with insecticides, so removing them by hand (where practical) is a great first step toward management.
No effective parasites or predators are currently reported. It is suspected by some that the white, woolly coating on dogwood sawfly does not only make the larvae appear to be bird droppings, thus deterring potential avian predators, but also might play some role in deterring insect predators and parasitic wasps. The yellow and black mottled coloration that the older (wandering) caterpillars develop is also suspected to play some role in camouflaging the insect.
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 nurseries, 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.