Redheaded Pine Sawfly (Neodiprion lecontei, order Hymenoptera, family Diprionidae) is so-named because of the markedly red head capsules of the larvae. It’s one of the most damaging conifer sawflies found in Ohio owing to its feeding behavior, wide host range, and the occurrence of two generations. First-generation larvae are in full swing with the second generation on the horizon.
The caterpillar-like larvae of this native sawfly may be found feeding on jack (Pinus banksiana), Japanese red (P. densiflora), loblolly (P. taeda), pitlolly (P. rigida X taeda), mugo (P. mugo), pitch (P. rigida), red (P. resinosa), Scotch (P. sylvestris), shortleaf (P. echinate), and Virginia (Pinus virginiana) pines with white (P. strobus) and Austrian (P. nigra) pines serving as occasional hosts. Cedar (Cedrus spp.) and fir (Abies spp.) may table fare for redheaded pine sawfly larvae if they run out of preferred hosts.
The sawfly spends the winter in the soil or duff beneath host trees as pre-pupae inside cocoons. Pupation and adult emergence occur in the spring. Sawflies are so named because adults resemble flies, and the females have saw-like ovipositors. The females use their ovipositors to insert eggs into needles.
First instar larvae that hatch from the eggs are too small to consume entire needles. Instead, they feed along the needle's edges producing clusters of dead, curled, straw-colored needles. Later instars consume entire needles.
This feeding behavior and symptomology are characteristic of several other "pine sawflies" found in Ohio including the European pine sawfly (N. sertifer). However, the European sawfly only has one generation per season and confines its damage to old needles.
Redheaded larvae feed gregariously in groups commonly referred to as “colonies.” The colonies usually include 10 – 20 individuals and are found on the needles of terminal stems. Colonies may be revealed by reddish-brown sawfly frass (= excrement) beneath infested trees.
If the colonies are disturbed, the larvae will lift their front and rear end, usually in unison, and regurgitate droplets of a chemical stew acquired from the pine needles. This defense strategy against predators is common among conifer sawflies. It also gives them great entertainment value.
The significance of this sawfly having two generations is that their conifer hosts are subjected to defoliation throughout much of the growing season with both the current and previous year's needles consumed. Once larvae have stripped the needles, they feed on bark tissue with heavy damage killing the affected branches. Heavy defoliation coupled with stem dieback can disfigure and even kill small trees.
As a native insect, redhead pine sawflies have a plethora of natural enemies. It’s one reason sawfly populations can rise and fall dramatically from year to year. Thus far, over 50 predators and parasitoids have been identified that will target these sawflies. Some may seem surprising like yellowjackets (Vespula spp. and Dolichovespula spp.), bald-faced hornets (D. maculata), and paper wasps (Polistes spp.). However, sawflies are commonly macerated by these predators to serve as protein for their young.
All instars feed in colonies making them easy to control by knocking them off into a bucket of soapy water. Or you can knock them onto the ground and do the "sawfly two-step” dance.
Insecticidal soaps are effective, but only against very early instar larvae. Topical applications of an insecticide labeled for on the conifer host will suppress sawfly populations; however, there’s always a risk of also killing the predators and parasitoids that help keep populations in check. Check the label to see if the insecticide is gentle on beneficial insects.
Finally, although sawfly larvae look like caterpillars (order Lepidoptera), sawflies belong to the same order as bees and wasps (Hymenoptera). Thus, caterpillar-control products based on the naturally occurring bacterium Bacillus thuringiensis var. kurstaki (Btk) will not be effective for controlling redheaded pine sawfly, or any other sawfly.