Two leaf feeding insects have been abundant in the Twin Cities and their damage has the peoples' attention. They are honeysuckle plant bugs and elm leaf miners. Both have trees looking thin and stressed across the seven county Region. There are seven species of plant bug (as well as two treehopper species) that attack honeylocusts, although only one has been given the name honeylocust plant bug, Diaphnocoris chlorionis. It produces one generation per year and overwinters as eggs. The eggs hatch soon after bud break and the young begin feeding immediately. The most serious damage occurs as the young feed on those leaves not yet unfurled. But the adults continue to feed on the same leaves, so the damage is accumulative through early July. Feeding injury causes very small stunted and misshapen leaves. Severe damage resembles caterpillar defoliation because only the petioles are clearly seen. Heavily damaged honeylocusts are beginning to refoliate now. If nothing else hits them, the trees should start looking a little better over the next month.
The elm leaf miner feeds between the top and bottom leaf surfaces. The damage creates brown translucent windows' or blotches in the leaves that later dry, curl and drop out. Severe damage can cause leaves to brown completely. The adult is a black sawfly that emerges in early May. The female cuts and lays eggs in leaf slits. The legless larvae feed inside the leaves until early summer and then drop to the ground to pupate. So although the damage is at it's peak now, control efforts are too late. Watch them closely over the next month or so for signs of wilt.