They can be distinguished from maggots of leafmining flies by looking with a hand lens for the presence of a head capsule and mandibles. The fourth and fifth instars are green to gray, with two black spots and several smaller white spots on each segment. Heavily infested leaves may be reduced to a network of veins.
Most damage occurs in the top third of plants.
Severe defoliation may cause bolls to open prematurely, and also cause shedding of squares and small bolls. The use of Bt cotton. Infestations usually begin at the edges of a field or in sandy streaks where plants are stressed. Check these areas first for damage to upper leaves. Treatment timing is critical because sprays cannot reach leafmining instars or horseshoe-stage larvae.