European Pine Sawfly

The European Pine Sawfly, Neodiprion sertifer (Geoffroy), is the most common sawfly found infesting pines in landscapes, ornamental nurseries and Christmas tree plantations. Sawfly larvae look like caterpillars but they are the larvae of primitive wasp-like insects. They are common from southwestern United states. This pest was accidentally introduced from Europe.

Mature larvae are grayish green, 18–25 mm long, and caterpillarlike in appearance. They have three pairs of thoracic legs and seven pairs of fleshy abdominal prolegs on the lower side of the abdomen. Mature larvae have shiny black heads and five characteristic stripes that run parallel along the length of their bodies.

On each side of the body are two adjacent stripes the one nearest to the legs is dark green or black and the stripe located right above it is grayish green. A light green stripe runs directly down the middle of the back of a mature larva. The eggs appear as an even spaced row of light brown spots along the length of a pine needle. Adults are wasplike, brown to black, and approximately 10-12 mm long.

Life Cycle: 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.

Damage: Pine sawflies usually feed on young trees, preferably 0.3 to 4.6 m tall. Trees growing under stress in shallow soils, very wet or dry sites, or under stress from competing vegetation are especially susceptible to infestation and heavy defoliation. Outbreaks occur periodically and tend to subside after a few years of heavy defoliation. Severe outbreaks have resulted in death or deformity of young pines.

The first instar larvae the ones hatching from the egg can only eat the needle surface, causing the needles to turn brown and wilt, giving a straw-like appearance to the needles. As the larvae grow, they remain together and feed from the tip of a needle to the base. The larvae feed on older foliage and move from branch to branch as they strip the needles. Trees which are entirely defoliated are severely stunted, but since the new growth is rarely attacked, the trees will survive. Larvae will often migrate to new trees if the needles on their current host have been devoured. Heavily infested trees end up with a bottle brush effect all the old needles are missing and only the current year’s needles are present.

Controls: Naturally occurring parasites and predators work against all European pine sawfly developmental stages, but achieve minimal control in most cases. Intervention is necessary to protect pines against European pine sawfly larval feeding damage. The larvae’s defined feeding period makes this task easier. The key is knowing exactly when larvae emerge from overwintered eggs. This can vary from year to year depending on temperatures the previous winter and current spring. To make monitoring easy, select a nice winter day and inspect needles closely for the presence of eggs. Mark several egg-laden terminals with white twist-ties. Beginning in March, use the ties to locate infested needles. Periodically inspect them for the presence of newly emerged larvae.

Another monitoring tactic is to permit larvae to feed for a short time until whitened terminals reveal themselves among the green, worm-free terminals. It is best to control European pine sawfly larvae when they are small and have not caused much feeding damage. While pruning out infested terminals is a control option, the removal of an excessive number of infested terminals might result in a plant with an undesirably sparse appearance. In these situations, insecticidal treatments can be used to eliminate sawfly larvae. European pine sawfly larvae are susceptible to a number of insecticidal products.

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