European Pine Sawfly

Neodiprion sertifer
Pine Sawfly are distributed throughout the area where their preferred hosts grow.
Species of Pine Sawfly will infest eastern white pine, P. strobus; Austrian pine, P. nigra; ponderosa pine, P. ponderosa; shortleaf pine, P. echinata; and pitch pine, P. rigida, if they grow in close proximity to preferred pines.t, P. strobus; Austrian pine, P. nigra; ponderosa pine, P. ponderosa; shortleaf pine, P. echinata; and pitch pine, P. rigida, if they grow in close proximity to preferred pines.

Conifer sawflies are a unique group of defoliating insects.

The larvae are host specific and feed on old and current year foliage at some point in their development. Some species have one generation per year with defoliation occurring in the spring and others produce three or more generations with defoliation occurring on into fall. Fall defoliation has a greater impact on trees and it is for this reason that sawflies having multiple generations are considered more devastating.

Sawfly adults resemble large houseflies but are actually primitive broad-waisted wasps. While true flies have one pair of wings, the sawfly has two pairs of wings. The females are equipped with an ovipositor that is serrated, which enables them to saw little slits in the needles where eggs are laid, thus the name “sawflies”.

Defoliation by sawflies is sporadic, occurring in localized or region-wide outbreaks lasting one or more years. Growth loss the year following a severe defoliation (greater than 75%) can average over 50% and mortality increases due to secondary invasion by bark beetles and pine sawyers.

During September and October females slit the edges of pine needles with saw-like structures on the tip of their abdomens and lay eggs into these openings. Females usually select needles grown that year located near the end of a lateral branch. Typically, one female will lay 6–8 eggs in a single needle in each of approximately 10–12 needles. Only one generation occurs per year and this species overwinters as eggs. Hatching occurs from late April through early May and larvae begin to feed in groups on the previous year’s needles and sometimes the bark of new shoots. If larvae defoliate the tree of last year’s needles before reaching maturity, they will crawl to another host tree to continue feeding. In late May and early June mature larvae usually drop to the ground to prepare to undergo the transformation to the pupal stage. In late August mature larvae begin to pupate inside tough, golden brown cocoons in the leaf litter. Adults emerge from early September until late fall.

The larval stage of this pest causes damage to several different species of pine. It prefers mugo pine, P. mugo; Scots pine, Pinus sylvestris; red pine, P. resinosa; jack pine, P. banksiana; Japanese red pine, P. densiflora; and table mountain pine, P. pungens.

Young larvae eat the surface of the needle causing needles to appear dry and strawlike. Older larvae continue to eat the needles from tip to base. Repeated defoliation severely stunts the growth of the tree and results in a thin, unsightly appearance. This aesthetic damage is most apparent on mugo pine in landscapes and nurseries and Scots pine grown in Christmas tree plantations. Since larvae rarely attack new foliage and most trees are seldom entirely defoliated, pines usually survive an infestation.
Although larvae can also feed on the bark of new shoots causing shoot deformation and twig mortality.14