The time required to grow from egg to adult is between 3 to 4 weeks. Damaged seed may germinate, but there may not be enough food reserves left in the seed for the plant to survive. Maggots feed in the seed or on the underground parts of seedlings. Maggots are dirty white with a yellowish tinge, legless, cylindrical, and tapered full-grown maggots reach 1/5- to 1/4-inch in length. Eggs hatch in a few days and the maggots work their way into the soil in search of food. Tiny, white, elongated eggs are deposited among debris and around plant stems near the soil surface. The adults are brownish-gray flies that closely resemble common houseflies except that they are about half the size. The adult flies emerge from puparia during late April and early May. Seed corn maggot puparia can be found in soil throughout the year, and they overwinter in these puparia. Maggots pupate inside a dark brown capsule-like puparium that resembles a grain of wheat. Seedcorn maggots invade vine crops, beans, and sweet corn. They may remain on the plants until first harvest because beans are self-pollinated (beans don't need insects for pollination). Plant covers increase the temperature by 5☌ and humidity by 25 percent inside the cover. Several types of lightweight, spunbonded fabrics, commonly called floating row covers, are economical and work well as an insect barrier. Also, commercial plant covers can be used as a physical barrier to exclude insects, to promote earlier yields, and to provide protection from wind and light frost. Adequate plant populations can usually be achieved by doubling the seeding rate, then thinning the plants to the desired population. Seed corn maggots, potato leafhoppers, Mexican bean beetles, aphids, and mites are the most common insects to attack beans (see illustrations, back page).
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