Life Cycle
There are many similarities in the life cycles of the northern and western corn rootworm. Both overwinter in the egg stage in the soil. Eggs, which are deposited in the soil during the summer, are American football-shaped, white, and less than 0.004 inches (0.10 mm) long. Larvae hatch in late May or early June and begin to feed on corn roots. Newly hatched larvae are small, less than 1/8 inch long, white worms. Corn rootworms go through three larval instars, pupate in the soil, and emerge as adults in July and August. There is one generation per year. Larvae have brown heads and a brown marking on the top of the last abdominal segment, giving them a double-headed appearance. Larvae have three pairs of legs, but these are not usually visible without magnification. After feeding for several weeks, the larvae dig a cell in the soil and molt into the pupal stage. The pupal stage is white and has the basic shape of the adult. Adult rootworms are about 1/4 inch long. Western corn rootworms are yellowish with a black stripe on each wing cover. Northern corn rootworm beetles are solid in color and vary from light tan to pale green.
Timing of egg hatch varies from year to year due to temperature differences and location. Corn rootworm males begin to emerge before females. Emergence often continues for a month or more. In years with hot, dry summers, numbers of western corn rootworm beetles may decline rapidly after mid-August, although in summers with less extreme conditions they may be found up until the first frost.
Females mate soon after emergence. Western corn rootworm females need to feed for about two weeks before they can lay eggs. Temperature and food quality influence the pre-oviposition period. Females typically lay eggs in the top 8 inches (200 mm) of soil, although they may be laid more than 12 inches (300 mm) deep, particularly if the soil surface is dry. Western corn rootworm females are more likely to lay some of their eggs below the 8-inch (200 mm) depth than northern corn rootworm females.
Read more about this topic: Western Corn Rootworm
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