Weevil

Weevil common name applied to a group of beetles of the order Coleoptera, having a snout or rostrum. Also known as snout beetles, these insects are placed in a large group known as Rhynchophora. True weevils belong to the family Curculionidae, the largest family of Coleoptera.

Most weevils have long, elbowed antennae that may fold into special grooves at the sides of the snout. The mouthparts consisting mostly of powerful mandibles located at the end of the snout for chewing seeds, vegetable matter or wood. Weevils are mostly dull coloured, but some are beautifully decorated. Many weevils have no wings; others are excellent fliers. Most weevils are less than 6 mm in length, although the largest member may exceed 75 mm, some weevils are so small as to be hard to see with the naked eye.

The snout is very variable in development. It may be either as long as or longer than the body; short and broad; or even absent (Scolytidae). Weevils as a group have probably been successful because of the development of their snout which is used not only for penetration and feeding, but also for burrowing holes for laying eggs.

Majority of weevils feed exclusively on plants and are found wherever seed producing plants occur. Both adults and larvae (grubs) cause damage. The weevils lay their eggs in the stem, flower, fruit or seed of the host plant. The larva is apodous (legless) and feeds on the flower head, fruits, seeds, stem or roots. Many larvae may feed on a single plant species, or closely related species. Adult weevils tend to be less specialised in their feeding habits.

The Rhynchophora includes a number of families. The members of family Scolytidae (Bark beetles) are found in living or dead wood. Cyladidae contains the common sweet potato weevil, Cylas formicarius, a red and blue ant-like species, often a serious pest of sweet potato. Curculionidae includes numerous economically important species. The mango fruit weevil (Sternochetus frigidus), mango stone weevil (S. mangiferae), leaf-cutting weevil (Deporaus marginatus), and the leaf miner (Rhynchaenus mangiferae) are pests of mango. Banana stem weevil (Cosmopolites sordidus) and root weevil (Odoiporus longicollis) are pests of banana. Apion corchori is the jute stem weevil and considered as a major pest. The red palm weevil (Rhynchophorus ferruginous) causes considerable damage to coconut. Other important curculionids of Bangladesh include the genera Attelabus, Alcides, Nanophyes, Apoderus, Balaninus, Desmidophorus, Myllocerus, Tanymecus, etc.

More than one species of weevils are pests in the storehouse. The most destructive one is the rice weevil, Sitophilus oryzae which infests rice and other cereals in storage. The maize weevil, Sitophilus zeamais is harmful to maize, wheat and other grains. [Monawar Ahmad]

See also beetle;insect. [Ahmad, Monawar Professor of Entomology, Bangladesh Agricultural University]