Diabrotica
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Diabrotica balteata |
Diabrotica is a widespread genus of beetles, sometimes referred to as cucumber beetles or corn rootworms, in the family Chrysomelidae. Members of this genus include several destructive agricultural pest species. Corn rootworms are one of the most economically destructive insects of maize in the United States. The Western corn rootworm, D. virgifera virgifera, and the Northern corn rootworm, D. barberi, are the most devastating rootworm species in Iowa, a major corn-growing area. A third species, the Southern corn rootworm, D. undecimpunctata howardi, causes much economic damage in other regions. Corn rootworm larvae can destroy significant percentages of corn if left untreated. In the United States, current estimates show that 30 million acres (120,000 km²) of corn, out of 80 million acres (320,000 km²) grown, are infested with corn rootworms and the number of infested acres is expected to grow over the next 20 years. The United States Department of Agriculture estimates that corn rootworms cause $1 billion in lost revenue each year, which includes $800 million in yield loss and $200 million in cost of treatment for corn growers (The Dow Chemical Company).
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[edit] Species
Several species of Diabrotica are significant pests in North America. They include:
- Banded cucumber beetle, Diabrotica balteata
- Northern corn rootworm, Diabrotica barberi
- Spotted cucumber beetle (a.k.a. Southern corn rootworm), Diabrotica undecimpunctata howardi
- Western cucumber beetle, Diabrotica undecimpunctata tenella
- Western spotted cucumber beetle, Diabrotica undecimpunctata undecimpunctata
- Western corn rootworm, Diabrotica virgifera virgifera
- Mexican corn rootworm, Diabrotica virgifera zeae
[edit] Diabrotica undecimpunctata
Adults of D. undecimpunctata are greenish-yellow with six large black spots on each elytron. They are about half a centimeter long. The larvae are yellowish and wormlike. D. undecimpunctata comprises three subspecies — Diabrotica undecimpunctata howardi (Southern corn rootworm or spotted cucumber beetle), Diabrotica undecimpunctata tenella (Western cucumber beetle) and Diabrotica undecimpunctata undecimpunctata (Western spotted cucumber beetle).
[edit] Diabrotica virgifera
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 (Wright). The eggs are deposited in the soil during the summer, and are football-shaped, white, and less than 0.004 inches 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.
[edit] References
[edit] General references
- R. Wright, L. Meinke & K. Jarvi (July 1999). Corn Rootworm Management. University of Nebraska. Retrieved on 2007-02-03.
