22.1 INTRODUCTION

About 75% of animal species in the world are insects. Some are beneficial predators and pollinators, but many are pests, acting as competitors for food. Others are vectors of infectious and parasitic disease. Not surprisingly, man has always tried to control such pests. In the past, preparations containing sulfur, arsenic compounds, extracts of tobacco and chrysanthemum, and strychnine were used, but only the synthetic pesticides produced by application of modern chemistry has been really successful. The agricultural yield has increased dramatically over the last 50 years and biocides have played a major role in this. Unfortunately, many of the compounds used may be harmful to the environment when used carelessly.

A biocide is any substance used with the intention of killing living organisms. A pesticide is defined as any substance or mixture intended for preventing, repelling, and destroying or mitigating any pest. The ideal pesticide is one that is toxic primarily to the target pests and is rapidly inactivated in the environment but few such pesticides exist. The development of more selective, less persistent, and safer pesticides is one of the great demands on modern chemistry. Based on presumed selectivity, biocides and pesticides may be classified into the groups shown in Table 22.1.