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boll weevil
The boll weevil (''Anthonomus grandis'') is a beetle which feeds on cotton buds and flowers. Thought to be native to Central America, it migrated into the United States from Mexico in the late 19th century and had infested all U.S. cotton-growing areas by the 1920s, devastating the industry and the people working in the American south. During the late 20th century it became a serious pest in South America as well. Since 1978, the Boll Weevil Eradication Program in the U.S. allowed full-scale cultivation to resume in many regions.
==Life cycle==
Adult weevils overwinter in well-drained areas in or near cotton fields after diapause. They emerge and enter cotton fields from early spring through midsummer, with peak emergence in late spring, and feed on immature cotton bolls. The female lays about 200 eggs over a 10–12 day period. The oviposition leaves wounds on the exterior of the flower bud. The eggs hatch in three to five days within the cotton squares (larger buds before flowering), feed for eight to ten days, and finally pupate. The pupal stage lasts another five to seven days. The life cycle from egg to adult spans about three weeks during the summer. Under optimal conditions there may be eight to 10 generations per season.
Boll weevils will begin to die at temperatures at or below −5 °C (23 °F). Research at the University of Missouri indicates they cannot survive more than an hour at −15 °C (5 °F). The insulation offered by leaf litter, crop residues, and snow may enable the beetle to survive when air temperatures drop to these levels. The boll weevil lays its eggs inside buds and ripening bolls (fruits) of the cotton plants. The adult insect has a long snout, is grayish color, and is usually less than 6mm long.
Other limitations on boll weevil populations include extreme heat and drought. Its natural predators include fire ants, insects, spiders, birds, and a parasitic wasp, ''Catolaccus grandis''. The insects sometimes emerge from diapause before cotton buds are available.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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