Posted 6/6/01 Chisago County Master Gardener, By Jerry Vitalis Spring Tree Insects Earlier this spring, I wrote an article that reported the anticipation of an outbreak of forest tent caterpillars; better known as armyworms. I donít intend to repeat the article but I want to remind readers that indeed the armyworms are here. Remember that the worms are about two inches long. They are mostly blue and black with a row of white, footprints or keyhole shaped markings along the edge of their bodies. They feed on deciduous, hardwood trees and seldom feed on conifers. Healthy, mature trees can tolerate defoliation for two or three consecutive years, however young trees may need attention. Another type of worm that has been seen falling from elm trees this spring is the immature fly larva, known as gall midges. These gall midges attach developing winged seeds in early spring. Later in the spring they mature and drop to the ground to pupate. These worms are very small and reddish in color. They do not injure elms so no control is needed. They can be a nuisance when large numbers fall onto driveways, sidewalks or other areas under elms, but the problem should be short-lived. If you have any mature birch trees, you probably get an annual visit from birch leafminers. This is the insect that causes the leaves to turn brown and make the birch tree look unhealthy, but it is actually o.k. The birchminer overwinters as pupae. In the spring, the adults hatch and fly to the birch trees. Eggs are inserted singly into the expanding leaves and the larvae hatch soon after. They feed on the plant tissue between the leaf surfaces, creating mines. Despite the unattractiveness of the brown leaves, the treeís health is usually not at risk. Birch leafminers have two generations; the second appears approximately in mid-June. Damage from the second generation is less severe then the first. Control is rarely, if ever needed, for the treeís health. You can manage leafminers with a foliar systemic insecticide application (acephate - Orthene or dimethoate- Cygon). You can also hire a professional to spray large trees if you feel the need. Another tree insect is the pine spittlebug that feeds on conifers. As a nymph, the pine spittlebug has a black head and thorax with a light colored abdomen. It is found on the shoats of pines and feeds on the sap with piercing, sucking mouthparts. Its frothy foam helps protect it from the environment and natural enemies. Nymphs hatch in spring and generally feed until early July. They mature into adults about mid-July. They are a mottled gray, brown and black and they don't make a spittle mass. As with the other insects mentioned in this article, damage to healthy trees is rarely severe. Parts of the research for this article is taken from the writings of Jeff Hahn, Assistant Extension Entomologist at the University of Minnesota. ©Post Review