Adult Pupae Adult Hessian flies are small black flies about the size of a mosquito. Adults live for about two days, during which time they mate. Females lay about 200 eggs in the grooves of the upperside of wheat leaves. Eggs are orange-red, V32 inch long and hatch in three to five days. Newly hatched larvae move down the leaf groove beyond the leaf sheath to the stem where they begin to feed at the base of the leaf.
Maggots become white after the first molt and appear greenish-white when fully grown.
Maggots suck sap and stunt tillers, possibly by injecting a toxin into the plant. Feeding by a single larva for several days is sufficient to completely stunt or kill a vegetative tiller. Stunted vegetative tillers are dark green, do not elongate or produce new leaves, and usually die after the maggots pupate. Infested jointed stems are shorter and are weakened at the joint where feeding has occurred. Grain filling of infested stems is reduced and damaged stems often lodge before harvest.