Direct and Indirect Defence Against Insects

Abstract

To obtain nutrients from their hosts, insects feeding on plants use a variety of approaches. Instead of being submissive victims during such interactions, plants respond to these herbivores by producing a variety of defensins in the form of toxins, post-defence peptides, etc. so that the physiological or metabolic processes in the insect could be targeted (direct defence mechanisms) or emit volatile organic compounds to attract natural enemies of these herbivores (indirect defence). Direct and indirect defence mechanisms in plants may act together in concurrence or independent of each other. Both types of defence mechanisms could be either constitutive (always present in the plant) or induced (produced in response to damage or stress caused by herbivores). Evolution of induced chemical defences is linked with formation of chemical substances which are not involved in either photosynthetic or metabolic activities or growth development and reproduction of plants, but these organic compounds also known as secondary metabolites or allelochemicals are only required for defence against herbivores. These metabolites/toxins interfere with insect’s metabolism by blocking specific biochemical reactions. These natural defence mechanisms in plants (specially the induced one) could be exploited and used as an important tool in the field of pest management where one can restrict or cut down the use of large amount of insecticides or pesticides in crop fields.