Scarab Beetles-Scarabaeidae


Scarab Beetles-Scarabaeidae

This large family of Coleoptera contains some of the most remarkable and wellknown members of the insect world. Included are the sacred beetle of ancient Egypt, Scarabaeus sacer; the destructive Japanese beetle, Popillia japonica; and the impressive Hercules beetle, Dynastes hercules, the largest known beetle in the world.

Called scarab beetles, the members of this family occur in an assortment of sizes, shapes, and colors, and their habits vary considerably. They can be identified, however, by the unusual structure of their antennae, the last three or four segments of which are flattened.

Scarab beetles are divided into two large groups, the scavengers and the leaf chafers. The scavengers feed primarily on animal excrement, and are noted for their unusual manner in feeding their young. The scavenger scarab shapes bits of animal excrement into a ball about the size of a walnut which it then rolls along the ground. Frequently a second scavenger scarab appears and joins in pushing the ball along. The assistant often attempts to hijack the ball, but these attempts are seldom successful. The thief, although caught in the act, usually continues to help as though nothing had happened. The scavenger scarab and his partner roll the ball a considerable distance-by this time it has grown to the size of a baseball in many cases-and then bury it. The female will lay her eggs in the ball and the emerging larvae will feed on it.

Leaf chafers feed on the foliage of trees, and on pollen, flowers, fruit, and grass. Some pecies are feared by farmers, gardeners, and groundskeepers because of the enormous devastation they can cause.

Scarabaeinae. Within the large family Scarabaeidae are a large number of subfamilies. One of the most interesting of these is the subfamily Scarabaeinae, the dung beetles, or tumblebugs. Most members of this sub-family are black, but some species are colored a brilliant metallic green. Some species are horned. Scarabs of the genus Phanaeus, for example, have a single, long horn on the top of their head.

The most celebrated member of the subfamily Scarabaeinae is Scarabaeus sacer, the sacred scarab of ancient Egypt. This beetle was considered to be a symbol of life, a messenger of the Sun. The ball of dung it so laboriously rolled was thought to represent the earth and its rotation. In ancient Egyptian carvings it is designated by the syllable kheperi meaning to be, or exist. Scarabaeus sacer was also worshipped by other ancient civilizations, among them the Greek and the Roman. In these civilizations the image of this industrious beetle was frequently carved on precious stones worn as amulets.

Melolonthinae. Members of the large subfamily Melolonthinae all feed on plant materials. The most common beetles in this subfamily belong to the genus Phyllophaga; these are the May, or June, beetles-or June bugs, as they are frequently called. The adult June bug varies in length from about V2 inch to i inch. It is usually brown in color and has a stout body, slender legs, and a tiny head. The elytra have a lustrous finish.

Usually seen flying around lights in spring and summer, the adult June bugs feed on the foliage of trees and can cause severe damage. The larvae, however, are much more devastating than the adults, feeding on the roots and tubers of food crops.

Each female June bug lays from 50 to 200 pearly white cylindrical eggs. Each egg is buried from one to eight inches in the soil. The larvae, or white grubs, as they are called, hatch in about three weeks. The larvae first feed on decaying vegetation, but they soon begin to eat the roots of living plants. The larval stage lasts for about three years;

it is during the second year that the grubs cause the most damage. During this time they have an incredible hunger for the roots of such crops as corn and soybeans. They also devour the tubers of potatoes and the roots of bluegrass.

In the third year the June bug larvae pupate in an underground cell. They emerge fully developed in August or September, and then bury themselves in the ground until spring when they emerge again and feed on the foliage of trees. June bugs seem to favor the leaves of ash, pine, and walnut trees, and those of blackberry bushes.

The major enemy of the June bug is the Pyrgota fly, Pyrgota undata. The Pyrgota fly attacks the June bug in flight, when the beetle's tender back is exposed. It stabs the June bug with its sharp ovipositor and inserts a single egg. The June bug recovers from the initial attack, but about five days later the egg hatches and the emerging larva begins to feed on the body of the June bug. The June bug is soon weakened and unable to fly; a few days later, it dies.

The cockchafer, Melolontha melolontha, and the rose chafer, Macrodactylus subspinosus, are also distinguished members of the subfamily Melolonthinae. Cockchafers, like June bugs, feed on the leaves of trees and can strip entire forests bare of foliage. Rose chafers, found in sandy soil in many parts of the eastern United States, feed on flowers and fruit. The slender, long-legged rose chafers are sometimes eaten by poultry, but their body chemistry is poisonous and the poultry often die from their meal.

Rutelinae. Scarabs of the subfamily Rutelinae, the shining leaf chafers, are plant feeders. Many species of this subfamily are brightly colored and many are considered serious pests. Pelidnota punctata, for example, is a large yellow beetle that resembles the June bug. The elytra or front wings of P. punctata are marked with six black spots. Although the larvae of P. punctata feed on rotting wood, the adults are extremely destructive.

Easily, the most well-known pest in this subfamily, however, is Popillia japonica, the Japanese beetle.

The first Japanese beetles found in the United States were discovered near Riverton New Jersey, in 1916. Within a decade these small, shiny green beetles were firmly established over an area of nearly 2,500 square miles. Entomologists suspect that the first Japanese beetles came to this country as larvae or grubs, living in the soil surrounding imported Japanese nursery stock. If this is indeed the case, the young beetles must have enjoyed their Pacific crossing, for they are voracious root eaters.

In 1916, when American entomologists first began to study this exotic insect, little was known about P. japonica. After considerable research, it was discovered that this tiny scarab inhabited all the main islands of Japan, and that, in Japan at least, it was not a serious pest. However, this was sadly untrue for the American population of Ja-panese beetles. Before effective controls were established, this tiny green beetle was credited with causing some $10 million worth of destruction every year.

Why was the Japanese beetle a serious pest in the United States and yet relatively harmless in its homeland? This question led American entomologists to Japan and other countries in the ig2os in search of P. japoniccCs natural enemies. A large number of parasites and predators of the Japanese beetle were discovered, and many species were shipped to the United States in an effort to check the spread of P. japonica.

Of these imported insects, two parasites, Tiphia popilliavora from Japan and Tiphia vemalis from Korea, have proved extremely successful in containing the spread of the Japanese beetle in the United States. These parasitic small wasps lay their eggs on the bodies of Japanese beetle larvae. When the eggs hatch, the emerging young wasps feed on the Japanese beetle larvae, ultimately killing them. A number of more common animals also feed on Japanese beetles, among them starlings, sparrows, and moles.

Dynastinae. The subfamily Dynastinae contains the giants of the Scarabaeidae-the rhinoceros beetles, the Hercules beetles, and the elephant beetles. Many species of this subfamily are found in the eastern United States; they are also common in the tropics of Central and South America. Some are more than two inches in length. The largest member is the Hercules beetle, Dynastes hercules. Found in tropical Central America, the Hercules beetle often attains a length of more than seven inches.

The rhinoceros and elephant beetles are so named not only for their size, but also for the horns usually present on the head or pronotum of the males. Often these horns are forked or antlerlike, and often one of these scarabs will bear a remarkable resemblance to a rhinoceros or an elephant. Enema pan, for example, a member of this subfamily found primarily in Brazil, appears to be some form of miniature rhinoceros as it moves along the stalks of plants.

The smaller beetles in this subfamily members of the genera Ligyrus and Euethe' ola, for example-often feed on sugarcane, corn, and cereal crops. Several species are considered to be serious pests, both in their adult and larval stages.


INDEX : Insects   January 11, 2016 02:25:48 PM