INSECTS ish r i G By arshan D

INSECTS ish r i G By: arshan D vik Sath

Insect ? ? ? • Any member of the class Insecta, the largest class of the phylum Arthropoda is called an insect. • In a popular sense, “insect” usually means the familiar pests or disease carriers, from bedbugs, houseflies, and clothes moths to Japanese beetles and aphids; the annoyers, such as mosquitoes, fleas, horseflies, and hornets; and the conspicuous butterflies and moths. • Many insects are beneficial from a human viewpoint; they pollinate plants, produce useful substances, act as scavengers, and serve as food for other animals

ORIGIN • The most primitive insects known are found as fossils in rocks and lived about 350, 000 years ago. • Those insects originated with the terrestrial branch of the phylum Arthropoda. The Arthropoda, whose origin is thus far unknown, probably arose in Precambrian times, perhaps as much as 1, 000, 000 years ago.

INSECT: IT’S PARTS • The insect is covered by the cuticle, a layer of inert material laid down by a single sheet of epidermal cells. • In present-day insects, the primitive segments are grouped into three regions known as head, thorax, and abdomen.

HEAD • The first six segments have fused to form the head. The appendages of these segments have become modified into antennae that bear numerous sense organs and mouthparts that convey food to the mouth. Eyes also are prominent on the head. • Insect mouthparts have been modified strikingly and reflect particular methods of feeding.

THORAX • The insect thorax consists of three segments (called the prothorax, mesothorax, and metathorax), which may be fused but are usually recognizable. • Each segment bears a pair of legs, and, in the mature insect, the mesothorax and metathorax typically carry a pair of wings.

ABDOMEN • The abdomen consists of a maximum of 11 segments, although this number commonly is reduced by fusion. • In some insects, notably crickets and cockroaches, two feelers, or cerci, at the hind end of the abdomen bear sense organs. Jerusalem Cricket

Sensory perception and reception • Insects have an elaborate system of sense organs. Tactile hairs, concentrated on the antennae, palps, legs, and tarsi, cover the entire body surface. • Exceedingly sensitive organs called sensilla are concentrated in organs of hearing • Although the insect eye provides very poor form perception, insects by using a process of scanning probably can form adequate visual impressions of their surrounding • Insects have chemoreceptors, which help in reception of smell and taste.

INSECT COMMUNITIES • Social insects, however, have developed a division of labour in which the members must do the work required at the proper time. • If the society is to succeed, its needs must be communicated to the individual, and the individual must act. • E. g. : Bees, wasps Engine wasp

EFFECTS • Many insects are plant feeders; they damage crops • Direct injury to man by insect stings and bites is of relatively minor importance, • Swarms of biting flies and mosquitoes often make life almost intolerable.

Damage to growing crops • Insects are responsible for two major kinds of damage to growing crops. • First is direct injury done to the plant by the feeding insect, which eats leaves or burrows in stems, fruit, or roots. • The second type is indirect damage, in which the insect itself does little or no harm but transmits bacterial or, more frequently, viral infection into a crop

Commercial significance • Insects provide sources of commercially important products—for example, honey, silk, wax, dyes, pigments—therefore, insects can be of direct benefit to man. • The most important domesticated insects are the silkworm (Lepidoptera) and the honeybee (Hymenoptera). rp Silk ca et

ROLE IN NATURE • Insects and flowers have evolved together. Many plants depend on insects for pollination. Some insects are predators of others. • Insects aid bacteria, fungi, and other organisms in the decomposition of organic matter and in soil formation. pollination