Snout Beetles-Curculionoidea


Snout Beetles - Curculionoidea

The Curculionoidea are a superfamily of beetles including a number of important families, most of which are equipped with long beaks or snouts. The mouthparts of these beetles are small and usually hidden from view. In most cases, the mandibles, situated at the end of the snout, are the only mouthparts that can be seen without dissecting the insect. Commonly called snout beetles, the Curculionoidea include many serious pests of food crops, stored foods, and trees. Their larvae are often legless.


Brentids are easily recognized by their elongate body form; straight antenna; and long, often remarkably sexually dimorphic rostrum

The long, slender beetles of the family Brentidae, sometimes called the straight-snouted weevils, are usually found under bark or living in the nests of ants and termites. Most brentids inhabit the tropics; only six species may be found in North America. The most common North American species is Platysystrophus minutus, which is usually found under the bark of dead beech, poplar, and oak trees.

The brentids have long straight snouts that are usually chisel-shaped at the tip. The eyes are small and located a considerable distance from the mouthparts. In Zetophloeus pugionatus, a species found in Madagascar, the elytra are extended at the tips, causing this handsome black and red beetle to appear to have snouts at both ends.

Peculiar structural features are found in several other species of the Brentidae. Calodromus mellyi, for example, displays unusually structured hind legs in which the first tarsal segment is swollen, tipped with tufts of hair, and frequently almost as long as the beetle itself. C. mellyi is found in the East Indies.

The South American species Estenorrhinus designatus differs from other brentids in that its snout is short and thick and capped with large sharp mandibles.

Attelabidae. The so-called leaf-rolling weevils of the family Attelabidae are small, compact beetles, often beautifully colored in red and black. The females are notable in that each lays a single egg near the tip of a leaf and then proceeds to roll the leaf into a neat, cigar-shaped package.

When the egg is securely encased in this leaf roll, the female chews through the leaf near the stem and the roll drops to the ground. When the larva emerges from the egg, it feeds on the leaf ^oll and, in some cases, even pupates in it.

Apionidae. The tiny, pearshaped beetles of this family are usually seen in cultivated fields and on summer flowers. They are blue, dark green, or even orange in color. Their larvae often bore into plant stems, where they cause the formation of galls.

The Apionidae are divided into two sub-families. In members of the subfamily Nanophyinae the antennae are elbow shaped;

members of the subfamily Apioninae have straight antennae.

Curculionidae. This is the largest family of the superfamily Curculionoidea. Its members vary considerably in size, shape, and color, but in most species the snout is long. The antennae are usually located on the middle of the snout.

One of the most serious pests in this family is Calandra granaria, the grain weevil. This tiny black beetle is found in incredible numbers in such stored foodstuffs as rice, buckwheat, dried beans, peas, chestnuts, and wheat. C. granaria not only feeds on these materials-it often carries molds and fungi that cause more damage than the beetle itself.

Interestingly, the grain weevil avoids foodstuffs with a high oil content such as cocoa beans and green coffee. The grain weevil is a remarkably hardy insect, able to survive low temperatures and go without water for as long as 10 days. It has no rear wings and therefore must patiently wait to be transported from place to place.

Curculionids of the genus Curculio, commonly called nut beetles or acorn beetles, can be recognized by long, slender snouts that may be longer than the beetle itself. These beetles bore into nuts or acorns to lay their eggs. The larvae develop inside the acorns or nuts. Many species are regarded as pests. Curculio nucum prefers walnuts; C. elephas favors chestnuts and acorns; and C. caryae attacks hickory nuts and pecans.

Commonly found in North America, curculionids of the genus Lixus are elongate and usually somewhat tapered at both ends. They are usually found near water. One wellknown species is L. concavus, a black beetle covered with gray hair. Known as the rhubarb curculio, it is usually seen on the stems of sunflowers, dock, and rhubarb.

One of the most serious pests in this family is Anthonomus grandis, the boll weevil. The adults spend the winter months in woods or other protected areas. In the spring they move to cottonfields, where they feed on the blooms, seed pods, and bolls of cotton plants. The female lays her eggs inside the bolls. The eggs hatch in 3 to 5 days; the white larvae feed on the bolls for 7 to 14 days before pupating.

The boll weevil is thought to have traveled from Mexico to the United States in about 1800. Since then it has spread to most areas where cotton is cultivated. Several close relatives of the boll weevil are also serious pests, among them the strawberry weevil, Anthonomus signatus; the cranberry weevil, A. musculus; and the apple curculio, Tachypterellus quadrigibbus.

Scolytidae. Of all the insects, the small, dark, cylindrical beetles of the family Scolytidae are the most serious pests of trees. The family is divided into two groups: the bark, or engraver, beetles, and the ambrosia, or timber, beetles. The adults and larvae of both groups bore long tunnels or galleries in wood, an activity that eventually kills the trees in which they live.

Among the serious pests in this family are the fruit-tree bark beetle, SjQplytus rugulosus. which attacks cherry, peach, apple, and other types of trees. The European elm bark beetle, Scolytus multistriatus, is the carrier of the destructive Dutch elm disease. The clover root borer, Hylastinus obscurus, damages especially red clover. Two major pests on pine trees are Dendroctonus piceaperda and D. ponderosa.

The bark beetles live between the bark and wood of trees. The tunnels they bore etch the surface of the heartwood-thus the name engraver beetles-but do not actually enter the interior of the tree. The adults first bore through the bark of a tree and then dig a gallery or group of galleries in which the female's eggs are laid. When the eggs hatch, the larvae begin to bore their own tunnels, moving away from the gallery where they were born. They continue to dig throughout the larval stage, and then pupate at the end of the tunnel. The emerging adults then bore through the bark leaving the tree pocked with hundreds of tiny holes-and the cycle begins again.

The timber beetles, on the other hand, actually bore into the hardwood. They do not feed on the wood, preferring to get their nourishment from fungi they cultivate in their complex of galleries and tunnels. The females lay their eggs in small cells joining the main galleries, and the larvae are fed by the adults until they pupate. The adults supply the larvae with fungi and tirelessly carry away the excrement of their young in order to keep the galleries clean. When the adults fly to a new tree they carry with them bits of fungi, thus providing a continuing source of food.

All scolytids work in pairs or in family units consisting of a male and a harem of females. The various species of this family are characterized by the kind of trees in which they live and by the patterns made by the tunnels they bore.


INDEX : Insects   January 11, 2016 02:25:43 PM