Insecticides

Abstract

AbstractInsects constitute an immense drain on food resources worldwide, as well as being serious disease vectors. Insecticide applications are made directly to raw agricultural commodities to protect plants and animals from insect attacks. Official national and international bodies regulate pesticide use and set permitted maximum residue levels or MRLs/tolerances for residues of insecticides and degradation products. Insect vectors spread many human and animal diseases. It was estimated in 2000 by the World Health Organization (WHO) that malaria caused close to 3 milllion deaths annually. Major health and economic benefits are associated with the continued use of insecticides, and the combination of newly introduced chemical classes with improved understanding of pest management has done much to reduce both the amounts used and the risks to nontarget species and the environment. Historically, many insecticidal preparations were derived from plant species. Synthetic organic chemicals were introduced in the 1930s, but the scale of their use increased during the immediate postwar years, with the introduction of the chlorinated insecticides, the carbamates and the organophosphates. Chlorinated organic insecticides were used in quantity, particularly for control of disease vectors, but they became recognized as ubiquitous environmental pollutants. Their effectiveness fell as insect resistance became widespread. Newer insecticides based on substantially different modes of action and of greater environmental acceptability are replacing older compounds. Newer types include growth regulators, juvenile hormone analogs, compounds affecting other metabolic pathways, such as chitin synthesis, and compounds affecting insect behavior. Investigations of insect physiology revealed more details of the insect nervous system and identified new targets. Newer screening and synthesis techniques aided developmental work and resulted in newer insecticides effective at extremely low application rates. These include the synthetic pyrethroids, fermentation products such as the spinosads, that act at the nicotinic acetycholine receptor, as do the nitromethylenes compounds acting on the GABA receptor/chloride ionophore complex, voltage‐gated sodium channel effectors, and compounds acting on mitochondrial respiration, among others. Regulatory policy favors the development of new compounds that are compatible with integrated pest management (IPM) systems. Major considerations in selection of the proper insecticide for the IPM program include mode of action, timing, dosage of application, and problems of resistance and resurgence, possible effects of insecticide residues on food crops, and in the environment, and the impact of these on humans, domestic animals, and wildlife.