Landscape and Nursery - Pine Sawflies

Two defoliating species of pine sawflies are of concern to landscape and nursery professionals in our area. Both species prefer two and three needled pines such as mugo, Scots, red, and Austrian. The following is some information on these pests.

The European pine sawfly has one generation per year and larvae hatch from overwintered eggs laid in slits along needles. They feed until late May or early June. The red-headed pine sawfly has two generations. It overwinters as a mature larva and then quickly completes its life cycle in early spring. The first generation occurs in May-Early June and a second generation occurs in July-August.

These sawflies are chewing insects that look like caterpillars at first glance. However, don't use B.t. to control them! Sawflies are immature wasps/hornets and are not susceptible to B.t. sprays.
A quick way to tell the difference between “maggots” (immature flies), caterpillars (immature butterflies/moths) and sawflies (most plant feeding wasps) is by looking at the number of fleshy stumps called “prolegs” present along their abdomen. All maggots and slug sawflies (i.e. rose slug, pear slug) have no prolegs. Caterpillars will have 3-5 pairs of prolegs with tiny hooks on them called “crochets” because they resemble knitting needles. Most sawflies have 6-9 pairs of prolegs and no crochets such is the case with both red-headed and European sawflies.

Control sawflies by hand removal of infected terminals or by pesticide sprays. Two reduced-risk products, Azadirachtin (Neem many trade names) and Spinosad (Conserve, Entrust) have very good sawfly efficacy. Numerous biological controls such as birds, squirrels and beneficial insects exist for sawflies and often keep their populations low naturally,

Casey Sclar, IPM Coordinator, Longwood Gardens