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The Western corn rootworm, ''Diabrotica virgifera virgifera'', is one of the most devastating corn rootworm species in North America, especially in the midwestern corn-growing areas such as Iowa. A related species, the Northern corn rootworm, ''D. barberi'' co-inhabits in much of the range, and is fairly similar in biology. Two other subspecies of ''D. virgifera'' are described, including the Mexican corn rootworm (''Diabrotica virgifera zeae''), a significant pest in its own right, attacking corn in that country. Corn rootworm larvae can destroy significant percentages of corn if left untreated. In the United States, current estimates show that of corn (out of 80 million grown) are infested with corn rootworm. The United States Department of Agriculture estimates that corn rootworms cause $1 billion in lost revenue each year, including $800 million in yield loss and $200 million in cost of treatment for corn growers.〔The Dow Chemical Company〕 == 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 long. Larvae hatch in late May or early June and begin to feed on corn roots. Newly hatched larvae are small, less than long, white worms. Corn rootworms go through three larval instars, pupate in the soil and emerge as adults in July and August. One generation emerges each 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 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. 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 of soil, although they may be laid more than deep, particularly if the soil surface is dry. Western corn rootworm females are more likely to lay some of their eggs below the depth than northern corn rootworm females.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Western corn rootworm」の詳細全文を読む スポンサード リンク
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