|New Crop Production Handbook (Peace Corps, 1985, 390 p.)|
An insect belongs to a large group of animals characterized by a body divided into three parts: head, thorax, and abdomen, They have three pairs of jointed legs, one pair of antennae and from none to two pairs of wings,
Other classes of animals mistaken for insects due to certain similarities are:
1. Class Arachnida - Spiders, ticks, spider mites, etc. These are characterized by having only two main body parts and four pairs of jointed legs. They never have wings or antennae,
2. Class Crustacea - Lobsters, crayfish, sow bugs and pill bugs. This class is characterized by having five or more pairs of jointed legs, are wingless and may have two pair of antennae.
3. Class Chilopoda - The centipedes. This class of animals is characterized by having many body segments, Each of the body segments, with the exception of the head, has one pair of legs, They have one pair of antennae but the wings are absent,
4. Class Diplopoda - The millipedes. Millipedes are characterized by having many body segments, each with two pairs of legs. They have one pair or no antennae and wings are absent, Millipedes are rarely considered a pest.
Because many insects are beneficial and others are of little economic importance, it is essential that they are correctly identified, Common names vary from place to place and with conditions. For this reason, scientific names are used by entomologists. Proper identification is also important because chemical control may vary with certain closely related species,
Instead of an internal skeleton made up of bones, the insect has an external or exoskeleton, This cuticle or exoskeleton has an outside waxy or oily layer which helps to make it waterproof, This oily or waxy layer plays a part in the control of insects. When an insect walks over a surface sprayed with a contact insecticide, the oil on the surface of the cuticle dissolves some of the insecticide deposit from the surface. This dissolved insecticide is then absorbed through the cuticle of the insect and into the body fluid and the insect is poisoned.
The insect respiratory system is unlike that of the warm-blooded animals, It is a series of tubes which run to various organs of the insect's body some of which open to the outside. Fumigants used to kill insects enter the insect's body through these spiracles, Other control agents such as oil, may plug these spiracles and actually smother the insect.
Insects have several different types of mouthparts. The type of damage done by an insect pest depends upon the type mouthparts the insect has. These mouthparts are divided into five different categories: chewing, piercing-sucking, rasping, sucking, and lapping.
Insects with chewing mouthparts have a pair of mandibles or jaws which move laterally and can actually bite or chew holes in plant leaves, stems or other parts. Examples of insects with chewing mouthparts are various caterpillars or larvae such as cutworms, armyworms, corn earworms, grasshoppers, and beetles.
Some classes of insects have a sharp beak or needle-like styles with which they pierce the tissue of plants or animals. These are called piercing-sucking mouthparts. Plant feeding insects of this type suck out the plant sap or juices and may inject a toxin during feeding which cause characteristic symptoms on the plant. Some of these insects may also carry organisms which cause disease, usually viruses. Examples of insects and related animals with piercing-sucking mouthparts are the aphids, leafhoppers, mealybugs, squashbug, fleas, mosquito, etc.
Insects with rasping mouthparts injure the surface of the epidermis of the plant by breaking the walls of the surface cells and allowing the cell content to escape. These insects then suck up the cell sap. This can occur on the leaves, on the flower, or on the surface of the fruit, spoiling the market quality and causing the leaf to curl. Insects with this type of mouthpart are the thrips.
Insects with sucking or siphoning mouthparts are incapable of piercing plant or animal tissue. They merely suck up liquids which are readily available from the surface of the plants or the nectaries found in flowers. Examples of insects with this type of mouthpart are the adult moths and butterflies.
Lapping mouthparts are characterized by being broad and sponge-like. These mouthparts are used for sponging or lapping up liquids and transferring them to the mouth of the insect. Typical examples are adult flies, bees, ants, and wasps.
Because insects may cause damage during only one stage of their life cycle, a knowledge of the life cycle of insects is important. Insecticides might also be - effective during only one stage of the life cycle.