Weevils

Weevils (Curculionidae) comprise a very large group of insects that are closely related to beetles (order Coleoptera); more than 40,000 species are recognized worldwide, ranging in size from 0.2-2 in (0.5-5 cm). A weevil is easily distinguished from a beetle by its extended head, which forms a rostrum, and long, segmented antennae that are clubbed at the end and are usually bent in an elbow fashion near the base. Most species have a dull colouration—commonly brown, gray, or buff—but others are more brilliantly decorated with tinges of reddish brown, pale green, and blue. The body of most weevils is covered with a mass of tiny scales that give these insects an iridescent color. Adults usually have two pairs of wings, although several species are wingless and the elytra (wing cases) are fused together. Males are often smaller than females.

All weevils are herbivorous and feed off a wide range of plants. The small mouth is located at the tip of the rostrum. The chewing mouth parts, or mandibles, move in a horizontal manner in most species. In some, the rostrum is used as a boring tool, primarily to create a tiny hole for egg laying, or to reach the inner tissues of a plant stem. Adult weevils lay their eggs either directly on or inserted within their food plants. The larvae do not possess legs, and most feed within roots, stems, or seeds of a wide range of plants. Here they receive some degree of protection from predators such as birds, small mammals, and parasitic insects. When the larvae are fully grown they develop a cocoon and pupate; some root-living species pupate in the soil, but the majority appear to remain within the plant itself.

In view of their life history, weevils are of considerable economic importance, particularly in relation to agriculture. No part of a plant, from the roots to the seeds, is safe from the attacks of one or more species of weevil. Although it is mainly the larval stages that cause the most damage, the adults too can be quite destructive. Some species, such as the grain weevil (Sitophilus granarius), are serious pests of stored grains. Others, such as the cotton boll weevils (Anthonomus barbirostris), are responsible for widescale destruction of stored cotton in the United States, into which it was introduced in the 1890s from Latin America.