Biology and control of injurious insects

Abstract

Although many insect species are well-known pests of agricultural crops or play a part in the spread of human disease, it is by no means easy to measure the extent of the injury which we suffer. Because of the operation of market forces, the financial loss to crop producers may not reflect the real damage done by pests, while the importance attached to an insect-transmitted disease will depend to some degree on the incidence of other forms of mortality in the population concerned. The status of an insect as a pest may also change relatively quickly, as when it is introduced accidentally into a geographical area from which it was previously absent, or when changes in human activities and habits expose society to species which are then able to develop their previously unrealized potential for injury. Some insects are injurious over wide areas, others may be of very minor importance in some parts of their range or only occasionally reach levels of population density high enough to cause damage. Insects which are important pests under given forms of agricultural practice may become much less important when techniques of cultivation change, or may then be replaced by ‘new’ pests. These dynamic relationships between insect populations and human activities have an underlying ecological basis that needs to be studied carefully by those engaged in the control of injurious insects.