European pine sawfly

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European pine sawfly is a common, exotic, conifer sawfly. It is native to Europe. It was accidentally introduced into North America in 1925. It now occurs in the United States from Maine to Maryland, west to Minnesota and Missouri, and in western Washington and Oregon. It also occurs in southern Canada from New Brunswick to Ontario. It is the most common sawfly infecting pines in landscapes. The larvae are active from late April to mid-July. Adults are active from late August through September but are seldom seen. They are found in mixed and coniferous forests, parks, and yards.

In Minnesota European pine sawfly larvae feed on the needles of Scots pine, jack pine, and red pine. They rarely feed on eastern white pine. They feed on older foliage, avoiding needles of the current year. Young larvae consume only the outer tissue, leaving straw-like, twisted, skeletonized needles. Older larvae consume the entire needle. Defoliated shoots have a bottle brush appearance, with only a tuft of current year needles remaining at the tip. The larvae may also feed on young bark, causing the shoot to be deformed. Branches may die but the tree is seldom killed. European pine sawfly is considered a pest because it attacks Scots pine, which is cultivated as a Christmas tree; red pine, which is often used in pine plantations; and young trees, which are often used in landscaping.

Adults are slender, wasp-like, and 5⁄16″ to ⅝″ (8 to 15 mm) in length, and they have a ⅝″ to 1″ (15 to 25 mm) wingspan. They are mostly black with some yellow or orange markings on the thorax and abdomen. The head is black. The antennae on the female are long and have short, tooth-like extensions on one side (pectinate). On the male the extensions are very long, making the antennae appear feather-like on one side only.

Mature larvae are 11⁄16″ to 15⁄16″ (18 to 24 mm) in length. They are grayish-green with a pale longitudinal stripe on the back (middorsal), and on each side a dark stripe bordered by light stripes. The head is black. They look like small caterpillars but have six or more pairs of prolegs with no hook-like structures (crochets).

5⁄16″ to ⅝″ (8 to 15 mm)

Mixed and coniferous forests, parks, and yards

One generation per year: late August through September

When threatened, the larva rears back its head and thorax and raises the end of its abdomen, presenting a threatening appearance.

Adults are not strong fliers and are usually seen near a host tree.

The female creates a slit in a needle and inserts a single white egg. It is difficult to spot an infected needle until the first frost, when the tissue over the egg turns yellow or light brown. The needle then reveals an evenly spaced row of six to eight elongated, oval spots. The eggs overwinter and the larvae emerge in mid-April to early May. They pupate in a cocoon, either in a protected place on the bark or in duff on the ground. Adults emerge in the fall.

Sources

22, 24, 27, 29, 30, 82, 83.

Location: Woodbury, MN