Boll weevil

Description

The boll weevil (Anthonomus grandis) is a beetle that feeds on cotton buds and flowers. Thought to be native to Central Mexico, 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. The adult insect has a long snout, a grayish color, and is usually less than 6 mm (1⁄4 in) in length. Adult weevils overwinter in well-drained areas in or near cotton fields, and farms 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 boll weevil lays its eggs inside buds and ripening bolls (fruits) of the cotton plants. The female can lay up to 200 eggs over a 10- to 12-day period. The oviposition leaves wounds on the exterior of the flower bud. The eggs hatch in 3 to 5 days within the cotton squares (larger buds before flowering), feed for 8 to 10 days, and then pupate. The pupal stage lasts another 5 to 7 days. The lifecycle from egg to adult spans about three weeks during the summer. Under optimal conditions, 8 to 10 generations per season may occur. Boll weevils 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. Other limitations on boll weevil populations include extreme heat and drought. The weevil’s natural predators include fire ants, other insects, spiders, birds, and a parasitoid wasp, Catolaccus grandis. The weevils sometimes emerge from diapause before cotton buds are available.