Metabolism of Insecticides

Nowadays insecticides may be regarded as a normal environmental hazard for insects, survival over which has been achieved through natural selection of resistant strains. Though the purpose of this section is to outline the biochemical pathways by which insecticides are rendered harmless, it should be realized that resistance can also be developed, solely or partially, as a result of physical rather than metabolic changes in a species. This is because, ultimately, the degree of resistance is dependent on the rate at which an insect can degrade the toxic material so that lethal quantities do not accumulate at the site of action. Among the physical alterations that may lead to increased resistance are (1) a decline in the permeability of the integument (achieved by increasing cuticle thickness or the extent of tanning, or by modifying the composition of the cuticle); (2) a change in the pH of the gut, resulting in a decrease in solubility and, therefore, rate of absorption of an insecticide; (3) an increase in the amount of fat stored (most insecticides are fat-soluble and, therefore, accumulate in fatty tissues in which they are ineffective); (4) a decrease in permeability of the membranes surrounding the target tissue (usually the nervous system); and (5) a change in the physical structure of the target site.

Insects have various methods for detoxifying potentially harmful substances, many of which parallel those found in vertebrates. Hydrolysis, hydroxylation, sulfation, methy-lation, acetylation, and conjugation with cysteine, glycine, glucose, glucuronic acid, or phosphate are examples of the methods employed (Perry and Agosin, 1974; Wilkinson,

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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