Hessian fly, European gall gnat, Phytophaga destructor, so named because it was first observed in America shortly after the Hessian troops landed on Long Island in the American Revolution. It is one of the most destructive pests of wheat, barley, and rye. There are usually two generations a year but may be up to five. The adults, 1/10 in. (0.25 cm) long, live only a few days. They lay their eggs on plants, usually where the stems are covered by leaves; the larvae feed on the sap and weaken the plants so that they cannot bear grain. In its winter pupa stage the insect looks like and is called a flaxseed. Some control is achieved by planting winter wheat late, after the adult females have laid their eggs. The Hessian fly is classified in the phylum Arthropoda, class Insecta, order Diptera, family Cecidomyiidae.
See bulletins of the U.S. Dept. of Agriculture.