Toxicological and Chemical-Ecological Studies on Insect Control

Abstract

The purposeful rational design of insect control chemicals was based on studies of the mechanism and selectivity of insecticide action and of the chemical basis of insect behavior. I. Toxicological studies on insecticides. Studies on structure-activity relationships of nicotinoids demonstrated that the active nicotinoids should resemble acetylcholine with respect to their conformation and electronic makeup. The mode of insecticidal action elucidated provided the basis for developing new nitrogen-containing insecticides. Investigations on the fate of rotenone in various biological and photodecomposition systems and synthesis of its transformation products, as well as all possible stereoisomers of rotenone, enabled the analysis of the essential feature necessary for exerting its toxic action. A stereostructure defined by a 6aβ, 12aβ-configuration and hydrophobicity were essential. Also elucidation of the metabolic pathways of natural and certain synthetic pyrethroids formed the basis for understanding selectivity, resistance mechanisms, synergism and, with information on photoconversion, provided the groundwork for developing photostable pyrethroids. Reexamination of carbamates led to the finding of N-propylcarbamates, whose action was negatively correlated with the development of resistance of the green rice leafhopper to N-methylcarbamates. Recognition of the mechanism of action which involves the interaction with altered acetylcholinesterase led to the development of new anti-resistance insecticides. Thorough examination of the activation and deactivation reactions of thiono- or thiolo-phosphorus insecticides indicated the involvement of phosphorus oxythionate or sulfoxide intermediates. Such intermediates explained various chemical and toxicological results, and provided clues for developing new organophosphorus insecticides. II. Chemical-ecological studies on insect behavior. Callosobruchus chinensis and C. maculates have developed a strategy to reduce competition among larvae and to maximally utilize the host bean, first by marking the beans with exudates from their bodies and then killing the excess eggs using the same substances at accumulated doses. For mating, C. chinensis was found to produce a pheromone which induced the male to extrude his genital organ and to copulate with the female. All these ecochemicals were identified and their use for controlling the bean weevil is being developed. Sitophilus zeamais infests corn, wheat and rice grains. Chemical factors which cause such olfactory responses were identified. Also, chemical factors which cause attraction of the cheese mite, Tyrophagus putrescentiae, to cheese and other dairy and fermented food products were identified. Some work has been done on the defence substances produced by several Japanese stink bugs, Carabus procerulus and Damaster blaptoides oxuroides, as well as the osmeterium secretion of the caterpillars of swallowtail butterflies, and the trail-following pheromone of a Japanese termite, Reticulitermes speratus.