Forest Preserve District of Cook County, Illinois
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Weevils
Nature Bulletin No. 256   February 12, 1983
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

WEEVILS
Many of us have had the unpleasant experience of opening a bag of corn meal or a package of cereal and finding it alive with squirming weevils. These tiny grubs with whitish C-shaped bodies and dark heads are the larvae of a Snout Beetle or Weevil. The adult is a small inconspicuous dull-colored beetle with its head extended into a long down-curving snout resembling the trunk of an elephant. This snout is used by the female to drill holes in which the eggs are laid.

The weevils make up the largest closely-related family in the animal kingdom. There are over 35,000 kinds, with more than 2,500 species in the United States and Canada alone. All are strictly plant feeders and most kinds prefer some special plant. Relatively few are injurious to crops and those few are the most destructive insect pests known. The most famous is the Cotton Boll Weevil which entered Texas from Mexico in 1892. From there it spread until by 1922 it occupied practically all of the cotton-growing region of the United States. It is estimated that each person pays $10 per year extra for cotton goods because of the damage this weevil does and the cost of fighting it.

The adults are about 1/4 inch long. After spending the winter under piles of cotton stalks, dead leaves and trash, they emerge to feed on the young cotton plants and mate. When the flower buds or "squares" appear, the female uses the chewing jaws on the end of her snout to drill a deep hole in the bud where she lays a single egg. After three days, the egg hatches into a hungry white legless larva that devours the inside of the "square" and kills it. The full-grown larva, about 112 inch long, is followed by a resting pupa stage, lasting 3 to 5 days, from which an adult emerges to complete the cycle. There may be from two to ten generations in a season, depending upon the locality and the weather, and each female may lay from 100 to 300 eggs. The later generations lay their eggs in the cotton bolls produced by those flowers that bloomed, and their larvae destroy the bolls or injure them so that few seeds, with the lint or fibers attached, can develop.

The Granary Weevil and the Rice Weevil ravage grain, flour and meal in mills, elevators, ships, farms and homes, often causing total losses in stored grains of all kinds. The adults of both beetles are about 116 inch long, dark brown or black, and have short snouts. Usually only one larva feeds in each seed or grain, leaving only an empty hull. Both regularly occur together and are much alike except that only the rice beetle flies.

The young of another weevil, the Plum Curculio, causes "wormy" cherries, plums, peaches and other fruits with "stones", and also damages apples. The adults become active about blossom time, mate, and the females lay eggs in the newly formed fruits. As the larvae feed and grow, they cause much of the fruit to drop before it is ripe, or make it unfit for eating and marketing. The mature grubs leave the fallen fruit to burrow into the soil where they become transformed into another generation of little snout beetles distinguished by a shining black hump on each wing cover.

The clover leaf weevil, the alfalfa weevil, the strawberry weevil, the sweet potato weevil, and the sugar cane weevil -- to name only a few -- are other snout beetles which cause serious damage to crops. Last summer. the hazelnut weevil ruined what had promised to be a record yield. Another weevil with a very long snout attacks our hickory nuts. The acorn weevil is common in the acorns of many oaks and is relished by squirrels and woodpeckers.

The worms and weevils will get us yet.


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