Insect infestations and their effects on the growth and yield of field crops: a review

Abstract

A knowledge of the often complex relationship between insect populations and their effects on the yield-forming processes of crops is useful for assessing pest status and for devising methods of minimising the effects of infestation on yield. After a preliminary section on definition of terms, consideration is given to ways in which insects injure plants and crops, particularly annual crops. Investigations into the yield-forming processes of unattacked crops can often provide useful insights into the likely effect of insect injuries on yield. The differences between the characteristics of individuals and populations are discussed, both of insects attacking plants, and plants responding to the attacks of insects. The distribution of insects on plants and on crops and the effect that this has on damage is considered, as is the time and duration of the attack in relation to the growth cycle of the crop. The components of plant resistance to insect attack are then discussed, especially tolerance and the various ways in which plants and crops compensate for injury. The review concludes with an examination of the quantitative relationships between numbers of insects or injuries and their effects on yield. The generalised response is a sigmoid curve relating an upper and lower plateau of yield where changes in the numbers of insects or injuries have little effect. Most relationships conform to some part of this curve, though few show all its features.

Comparison of selection indices to identify sorghum genotypes resistant to the spotted stemborer Chilo partellus (Lepidoptera: Noctuidae)

“…Older larvae (3 rd instar) leave the whorl leaves and bore into the stem at the plant base, causing extensive stem tunneling that affects not only nutrient supply to the developing grain, but also results in partially or completely chaffy panicles. Stemborer damage also results in losses in fodder yield and quality (Bardner and Fletcher, 1974;Sharma, 2002). Global sorghum crop losses due to stem borer damage have been estimated at over US$ 300 million annually (ICRISAT, 1992;.…”

Damage effects of cereal aphids in wheat

“…This can cover large areas of a plant's epidermis and may hamper photosynthesis and promote senescence (Bardner and Fletcher, 1974); it promotes the growth of saprophytic fungi which may also have a negative effect on photosynthesis and leaf duration (Vereijken, 1979). These indirect effects, however, are scarcely investigated.…”

Nonrandom Distribution of Cabbage Aphids (Hemiptera: Aphididae) in Dryland Canola (Brassicales: Brassicaceae)

“…Conversely, we found high plot mean cabbage aphid densities at week 7, but plants in portions of the plots contained no or very few cabbage aphids. Spatially aggregated herbivorous insects may cause greater economic damage than equivalent populations with a more random or uniform distribution, as pest aggregations may increase the risk of over-coming crop plants' ability to tolerate or compensate for infestation levels (Bardner andFletcher 1974, Hughes andMcKinlay 1988). At the same time, spatial aggregations of pest infestations may reduce the ability of natural enemies to locate their prey.…”