By virtue of their mobility, fecundity and adaptable nature, insects are the most ubiquitous of invertebrate pests, causing problems to crops, clothing, property and the health of human beings and other animals in most parts of the world (Gullan and Cranston, 2000). The effects of insects are wide-ranging, from the direct destructive attack on crops and crop produce as well as timber and clothing, to the indirect effects of transmitting diseases of crops, livestock and human beings (Figure 4.1). The damage caused by insects is often immediately apparent, and it is not surprising that attempts to control infestations have been documented throughout recorded history.
Damage caused by insects is primarily associated with their feeding habits. Defoliation of crops, their consumption in storage, destruction of natural fabrics such as cotton and linen, and weakening of timber in wooden materials by woodborers are obvious symptoms of insect attack. In many cases it is the larval stage of the organisms concerned that cause the damage, although mature adults such as locusts can inflict catastrophic crop losses. In addition to direct consumption, excreta and the cast skins from insect moults may also contaminate crops, produce and other materials.
Insects transmit a wide range of diseases of both plants and animals. A few fungal, several bacterial and many viral diseases of plants are carried by insect vectors: many protozoan, as well as some bacterial and viral diseases of human beings and other animals are similarly transmitted (Table 4.1 and Lounibos, 2002).