Invertebrate Zoology: A Study Guide - T. A. Dauda 2014

Multicellular Animals
Arthropods
Subphylum Tracheata - Class Insecta - Orders with Complete Metamorphosis - Order Coleoptera, or Beetles

There are up to 350,000 known species of beetles. A distinctive feature of their appearance is the presence of a hardened first pair of wings—the elytra. When at rest, these lie flat along the back. Beneath them are folded the membranous wings of the second pair. The entire body of a beetle, especially the HEAD and the first segment of the Thorax, is covered with a thick layer of Chitin.

In flying beetles, the elytra are raised and spread apart. They act as supporting planes, while the second pair of wings serves as the propulsion apparatus. In some beetles, the elytra are shortened.

The head of beetles bears 1 pair of diverse antennae carrying Organs of Touch and smell, as well as 3 pairs of palps. The mouthparts are of the chewing type. The limbs are typically of the walking type, though in many species they are modified and adapted for a burrowing or swimming lifestyle.

Based on their feeding habits, beetles are divided into carnivorous and omnivorous types.

Many beetles are highly beneficial: they destroy insects that are mass pests of fields and gardens, and perform a sanitary function by disposing of animal waste and carcasses in nature. Predatory ground beetles (Carabidae), common in gardens and forests where they hunt various insects, are very useful. The most widespread among these are the garden ground beetle and the grainy forest ground beetle. Also extremely beneficial are caterpillar hunters (Calosoma), which are closely related to true ground beetles. These are large beetles that live in trees, where they destroy the hairy caterpillars of the pine moth, which many insectivorous birds avoid. The caterpillars are hunted not only by the beetles themselves, but also by their larvae.

Another group of beneficial beetles consists of ladybirds (ladybugs). The majority of these are predators both in the adult stage and as larvae. A typical representative is our seven-spot ladybird. Ladybirds and their larvae feed primarily on aphids and scale insects. For instance, a single seven-spot ladybird destroys up to 80 apple aphids per day, which accounts for more than 50% of its body weight. Very few herbivorous ladybirds can cause some minor damage to plants. Ladybirds and their larvae feature warning coloration. This coloration signals to animals that the prey is unpalatable. In addition, when a beetle is disturbed, a droplet of toxic hemolymph is released from the joints of its limbs.

The feces of various animals serve as food for many dung beetles and their larvae. For example, small dung beetles of the genus Aphodius (up to 8 mm long) flock to animal droppings, feed on them, and lay their eggs inside them. The developing larvae find themselves surrounded by an Abundance of food—dung, which they consume. Larger geotrupid dung beetles behave differently. They dig fairly deep burrows beneath a pile of dung, lay a single egg in each, and pack the burrows with dung, which serves as food for their larvae.

Of particular interest are the southern sacred scarab beetles. They sculpt balls of dung, roll them over considerable distances, and then dig burrows to store the balls inside. Some balls serve as food for the beetle itself, while in others the females lay eggs, in which the larvae develop. In dung beetles, the strong forelegs have wide tibias, toothed along the edge and adapted for digging.

Sexton beetles (burying beetles) use the carcasses of small and medium-sized animals as food for their larvae. Possessing a highly developed SENSE OF SMELL, these beetles fly to a carcass, dig a pit beneath it, and thus gradually sink the body into the ground. The females then lay their eggs, and the resulting larvae feed on the buried carcass.

Many beetle species are dangerous pests of trees and agricultural crops. In our country, cockchafers (may bugs) cause serious damage to the ROOT systems of young pine plantations. The western cockchafer is common in the western and southern regions, while the eastern cockchafer is found in the eastern regions. Cockchafers feed on the leaves of birch, oak, aspen, and other trees. The female beetles lay their eggs in the ground, where the larvae develop. Overwintering three times, they feed on the roots of tree seedlings, thereby causing great damage to forest plantations. Young pine forests and fruit-berry crops frequently suffer from cockchafer larvae. In southern regions, The Development of the cockchafer typically lasts 4 years, whereas in more northern areas it takes 5 years.

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Fig. 69 Click beetle (1) and its larva (2)

Serious damage to grain crops in the steppe zone of Russia is caused by the sunn pest beetle (or cereal leaf beetle)—a small (12–14 mm long) greenish-black insect with brownish elytra and a dark spot at their base. It feeds on ripened grains of wheat, rye, and barley. In forest-steppe regions and further north, the closely related field pest beetle is found. Both species can be numerous. The females lay eggs in the ground. The larvae live in the soil, where they feed on plant roots, causing thinning of the crop stands.

Click beetles are well known for their unique ability to jump into the air with a clicking sound when falling on their backs (Fig. 69). This is how the beetle rights itself. This jumping mechanism is due to the fact that click beetles have weak legs, making it impossible for them to roll over from back to belly like other beetles.

Fig. 70 Colorado potato beetle (A) and its larva (B)

Click beetle larvae live in the soil, under tree bark, and in tree stumps. These long, worm-like larvae are covered with a thick chitinous exoskeleton and are commonly known as wireworms. They feed on the underground parts of plants. Click beetles damage cereal crops, perennial grasses, and garden vegetables. The greatest damage is caused by the common wireworm, the dark click beetle, and the striped click beetle.

Another group of plant-damaging beetles is the leaf beetles (Chrysomelidae), numbering over 50,000 species. Among them, the Colorado potato beetle is well known to many (Fig. 70). Its native home is Mexico. It was first brought to Europe from America during World War I and spread across A number of Western European countries in a short period of time. The Colorado potato beetle invaded our country after the Great Patriotic War.

Colorado potato beetles settle on potato leaves and feed on them. They overwinter in the soil, and in the spring they begin feeding on the young foliage of potatoes, tomatoes, and wild nightshades.

After feeding, the beetles mate, and the females then lay eggs (up to 40 eggs per clutch) on the underside of potato leaves. Over its lifetime, a single female lays more than 500 eggs. There are usually 1 to 3 generations per year. Thus, the offspring of a single female, if allowed to reproduce without hindrance, can reach 250,000 by the end of summer. Within 5–15 days (depending on Temperature) after oviposition, larvae hatch from the eggs and, like the adults, feed on potato foliage. After 2–3 weeks, they pupate in the soil near the potato roots. On the 7th to 8th day of development, adult beetles emerge from the pupae.

Colorado potato beetles live for up to 14 months. They spread rapidly thanks to their ability to undertake mass migratory flights spanning several kilometers during dry weather. Control measures against these beetles in infested fields are carried out primarily through chemical Methods.

A large (about 30,000 species) and distinctive group of pest beetles is the weevils (Curculionidae) (Fig. 71). These small beetles are easily recognized by The Structure of the head, the front part of which is elongated into a rostrum (snout) bearing elbowed antennae and mouthparts.

Damage is caused primarily by weevil larvae. For instance, the larva of the beet weevil feeds on the roots of sugar beets. The female apple blossom weevil lays its eggs in the flower buds of pears and apples. The legless larvae hatched from the eggs hollow out the flower Ovary. One of the most serious pests is the granary weevil; its females lay eggs inside grain kernels, and the larvae consume the interior of the grain and pupate right there. A single female granary weevil typically lays up to 150 eggs. Adult beetles also cause damage by feeding on the grains.

Fig. 71 Beet weevil

Fig. 72. Eight-toothed spruce bark beetle:

A — adult; B — beetle galleries.

Bark beetles cause significant damage to forestry. They are considered secondary pests that typically attack weakened trees. Males of the eight-toothed spruce bark beetle (Fig. 72) bore into the wood and construct galleries. Females follow these galleries to join them, and mating occurs. Afterwards, the females chew new tunnels, make small niches in the walls, and lay their eggs there. The emerging larvae tunnel through the wood, and these passages gradually widen as the insects grow and develop.

At the end of these tunnels, the larvae pupate. The newly emerged beetles chew their way through the wood again and exit through emergence holes. Eight-toothed spruce bark beetles primarily damage spruce and other conifers, whereas birch trees are often attacked by the birch sapwood borer.

Forests also suffer heavily from longhorned beetles (Fig. 73), also known as cerambycids, which typically feature antennae longer than their bodies. These beetles lay their eggs in the tree bark. The hatched larvae burrow first into the bark and subsequently into the wood, where they eventually pupate. Typical representatives of this family include the small black spruce longhorned beetle, the great aspen borer, and the poplar longhorned beetle.

Fig. 73. Pine longhorned beetle

While most ground beetles are predatory and beneficial to humans, some species are herbivorous and typically medium-sized (14–20 mm). Among them, the millet ground beetle damages millet, corn, and other cereal crops, whereas the corn ground beetle feeds on wheat and rye grains.

Certain beetles, such as Water scavenger beetles, diving beetles, and their larvae, have adapted to life in freshwater habitats. Key aquatic adaptations include the modification of their third pair of legs into swimming paddles fringed with hairs, as well as The ability to store a reserve of air beneath their elytra. Aquatic beetles, particularly diving beetles and their larvae, can cause economic losses in fish farms by preying on fish fry.