Plant injury due to insects, mites, nematodes and other pests

Abstract

Many insects, mites and nematodes feed on plants, thereby causing injury and symptoms which can resemble those caused by pathogens. The damaged tissue may subsequently be colonized by fungi and bacteria, so that it is sometimes difficult to ascertain the primary cause of the symptoms unless there is evidence of pests in the form of excreta, eggs or other products. Pests are also involved in the dissemination, inoculation and occasionally in the overwintering of plant pathogens, and many wound parasites enter through lesions caused by pests. There are symbiotic relationships between insects and pathogens, in some cases apparently obligate for the latter. The plant pathologist investigating diseases in the field will almost certainly be confronted with these aspects at one time or another in his career, and a working knowledge of plant pests is likely to be useful to him. The reactions of plants to pathogens, pests and mechanical and chemical injury show many parallels which are of interest to all concerned with plant injury, and which lead to a fuller understanding of the problems involved.