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'Early spring' brought early insects

Jeff Hohn, U of M Assistant Extension Entomologist, stated that the early spring also brought-on some insects earlier than usual. I wrote about the tent caterpillars, but Hohn has also seen early activity from the European pine sawfly and pine spittlebug.

Sawflies are a group of insects related to wasps and bees that do not sting. The larval or immature stage of sawflies are plant feeders and look like hairless caterpillars. The main difference between sawflies and caterpillars is the number of prolegs (fleshy, leg-like projections) on the abdomen. Caterpillars have two to five prolegs while sawflies have six or more prolegs.

The larvae of the European sawfly are gray-green with a black head and legs. They have a single, light stripe down the back, two light green stripes and one dark green or black stripe on each side.

They overwinter as eggs in the previous season's needles. Larvae begin feeding around mid-May and continue through June. After feeding, larvae pupate in the soil or on the tree and adults begin appearing in early September through late fall. Adults lay eggs in the current season's needles near the ends of branches where they overwinter. There is one generation per year.

The larvae feed in groups on the previous year's needles and eat all the needles on a single branch before moving to another branch for continuous feeding. They seldom kill the tree because the new foliage is never eaten, however repeated defoliation can slow the tree's growth.

There are many types of sawflies in Minnesota with a slight difference in appearance in each of them. Management includes a variety of options. Usually if the tree is healthy, early detection and hand picking is all that is necessary. If you must use insecticides, know that Bacillus Thuringiensis (BT) will not control sawflies; BT is effective for the larval of butterflies and moths but not sawfly larval.

The pine spittlebug feeds on pines (Scotch, white, red, and jack), spruces, balsam fir, and hemlock. They are also called froghoppers, aphids, and scale insects. There are various species of spittlebugs in North America feeding on trees, herbaceous plants, and grasses. Many are harmless, but a few can cause serious damage to plants.

Adult spittlebugs resemble leafhoppers, but are longer and can be grey, brown, or black. They actively walk, hop or fly around plants. The adults are usually dull-colored with prominent eyes, while the nymphs are smaller and greenish-yellow. Eggs are laid in plant stems or between the stem and leaf sheaths of grasses. They overwinter in the egg stage and usually hatch in May. The small nymphs are wingless but otherwise resemble the adults.

The nymphs suck plant sap and cover themselves with a frothy mass of spittle that serves as a camouflage from predators and also protects them from the hot sun. Adults also feed on plants and although they don't make spittle, they excrete large amounts of undigested sap or honeydew.

Plant damage by spittlebugs can include stunting, dwarfing, and weakening of plants. Some spittlebugs complete their development on one host species, while others must have two different host species during their life cycle. Most spittlebugs produce only one generation per year.

Light infestations will have little damage to the trees so control measures are usually not necessary. If infestation is heavy (in May), use an insecticide soap or horticultural oil and be sure the coverage is thorough. Soil-applied systemic insecticides, like imidacloprid, are also effective.

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