Hylemya florilega (Meigen)
The bean seed maggot and the seedcorn maggot are important, injurious pests of bean fields throughout the state. These maggots damage seeds and seedlings of beans, corn, peas and various vegetable crops. Considerable injury and stand loss occurs in early planted beans.
The adult fly is l/4 inch long and resembles a house fly in color, but is smaller and more slender. The full grown maggot is white, l/4 inch long and lacks a visible head. The pupa is oval, reddish brown and 5/l6 inch long.
The life cycle of the bean seed maggot has four stages - egg, larva (maggot), pupa and adult. It overwinters as a pupa in soil close to old roots where it developed. Adults emerge in the spring as early beans are being planted. Females lay eggs, which hatch in less than a week, in moist soil containing decaying plant material upon which the young maggots feed. If sprouting seeds are near, maggots are attracted to them. Maggots reach full growth (pupae stage) in two to three weeks. Flies emerge two to three weeks later to start another generation; there are three to four generations each year.
Maggots reaching the seed as sprouting begins feed between the cotyledons and damage the plant embryo. Seeds with damaged germs die or develop into deformed plants which give low yields.
Maggots that attack after seeds sprout bore into the stem, usually causing the plant to wither and die. In early spring, if soil is wet and cold during seed sprout, damage is especially severe.
The only effective method to prevent bean seed maggot injury is to treat seed with an insecticide. Check the most recent Commercial Vegetable Production Guide or consult with your pesticide supplier or county agent for details of pesticide use.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Robert Tetrault, Extension Entomologist and Shelby Fleischer, Professor