The chemical inhibition of feeding by phytophagous insects: a review

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Abstract
Chemical inhibition of feeding has been studied in detail for only a few insect species, but inhibitory chemicals play a considerable part in host-plant selection by a wide range of phytophagous insects from several orders. Many different chemicals are involved, some of them amongst the normal constituents of plants. A few have a general effect, preventing feeding by all the insects which have so far been tested, but the majority are effective only against some species.Inhibition may function by blocking the input from receptors normally responding to phagostimulants or by stimulating specific ‘deterrent’ cells. The former may have a general effect on all insects, but chemicals in the latter category will only be effective if the insect has neurones capable of responding to them. Hence these will have more specific effects.Inhibitory chemicals may be applied to plants in the same way as insecticides, their advantage being that the parasite/predator complex of species not feeding directly on the plant will be unharmed. An alternative approach is to breed resistant varieties of plants by selecting for inhibitory attributes. Although many varieties of crops are known which are insect-resistant, the basis of the resistance is generally unknown. A more thorough understanding of the mechanisms involved in inhibition of feeding by chemicals would enable a more logical approach to be made to the development of resistant plants.