What can one weevil do in six generations?

By Chelsie Vandaveer

February 20, 2002

killerPlants Tendrils: ~~1~~2~~3~~4~~5~~

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In Brownsville, Texas in the autumn of 1894, people noticed a new insect. It was small, only about one-quarter of an inch (6 mm). Almost half the body length was a snout from which protruded two 'elbowed' antennae.

In less than 30 years, the cotton boll weevil (Anthonomus grandis Boheman) [an thon' o mus gran' dis] spread through the southern states and
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almost destroyed an industry.

The female boll weevil drills a hole with her snout into a square (the flower bud of cotton). She inserts her ovipositor into the hole and lays a single egg. When the egg hatches in 3 to 4 days, the larva feeds on the floral parts.

The flower flares or opens, but with petals and stamens useless. Infested flowers fall from the cotton plant. If the female can not find a square, she will lay her egg in a developing boll (seed capsule with fibers). The larva will feed on the cotton fibers.

The female boll weevil will lay six eggs a day, ruining that many flowers or bolls. She will live long enough to lay 300 eggs before she dies. When a boll weevil emerges as an adult, it will travel 2 miles or more in search of a new field of cotton.

In the warm states, the boll weevil will have six generations per year. If only 10 percent of each generation survive that single female could give rise to 729 million weevils in the sixth generation.

The final generation each fall appears like the adults of the previous generations. But their bodies do not sexually mature. Instead they store fat. They will migrate to forests or urban yards to hibernate. These boll weevils can live up to eleven months without eating.

The Texas Cooperative Extension Service has posted a photograph of Anthonomus grandis. To view the photo, click on the link:

http://entowww.tamu.edu/extension/youth/bug/bug067.html