by Eric R. Day and Ames Herbert, Virginia Tech
Identification
Adult-The adult weevil measures from 3 to 8.5 mm from the tip of the snout to the tip of the abdomen. It is usually reddish or grayish brown though its color may vary (yellowish brown to dark brown) according to its age and size. The conspicuous snout is about half as long as the body. A distinctive characteristic is the double-toothed spur on the inner surface of each front leg. Egg-The pearly white egg is elliptical and approximately 0.85 mm long. The soft shell permits the egg to fit into almost any cavity. Larva-The newly hatched larva is inconspicuous, being only slightly larger than the egg. The mature larva is white, legless, and about 13 mm long. Its head and mouthparts are brown; its body is curved and wrinkled. Pupae-White at first, the pupa becomes brown as it develops.
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Color Slides of the Boll WeevilScale showing size of Boll Weevil Top View of Boll Weevil Double spur on front leg: Other related weevils have only one spur Snout and Elbowed antenna: Note the relative long length of snout compared to head length Antenna: Note that hair or setae are found on ALL segments Side View of Boll Weevil
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BIOLOGY
Cotton is the only known host plant of the boll weevil in Virginia.
Damage-Injury is caused by both adults and larvae. Although adult females prefer squares, they oviposit into both squares and young bolls and seal the holes with excrement. Egg punctures become small, nipple-like protuberances. Larvae (developing within cavities) then feed within the squares, causing the bracts to open or flare, the color to fade to a yellowish green, and the plant to shed the infested squares. Limited feeding on the squares and bolls by adults usually does not result in shedding, but cotton fiber is sometimes ruined. Boll-rotting fungi may enter through egg and feeding punctures.
Life History-Boll weevils overwinter as diapausing adults sheltered under leaf litter, in woods, in weeds and along fence rows and ditch banks surrounding cotton fields. These adults begin to emerge as early as February in southerly areas and continue through early July, with peak emergence during late May and early June. In early spring the weevils feed primarily on terminals of cotton seedlings, but egg-laying does not occur until squares are present. Adult females make a small cavity in each square into which they deposit a single egg. First generation females lay an average of 200 eggs while late summer generations may average only 5 eggs per female. Eggs usually hatch in 2 to 4 days depending upon the temperature.
After the larvae begin to feed, the infested squares yellow, flare, and drop from the plant in about 3 days. Depending upon the temperature and nutritional value of their food, larvae complete their development in 7 to 12 days and then transform into pupae within the squares. This stage lasts from 3.5 to 8.5 days. Newly formed adults remain in squares 1.5 to 2.5 days before chewing their way out. Because of the prolonged emergence of overwintering adults, distinct generations are difficult to recognize.
IF YOU THINK YOU HAVE A BOLL WEEVIL IN VIRGINIA: Please take a sample to your local county extension office or contact the Virginia Department of Agriculture and Consumer Services.