RESIDUAL ACTIVITY OF ORGANOPHOSPHORUS AND PYRETHROID INSECTICIDES APPLIED TO WHEAT STORED UNDER SIMULATED WESTERN CANADIAN CONDITIONS

Abstract

AbstractWheat treated with 2,4, or 8 ppm of insecticide, on a whole-seed basis, was bioassayed with Tribolium castaneum (Herbst) and Cryptolestes ferrugineus (Stephens) adults at 30 °C and 70% RH after 4 days, 2 weeks, and then at eleven 1-month intervals. Malathion was more toxic to C. ferrugineus than to T. castaneum whereas the reverse was true for pirimiphos-methyl; malathion showed little effectiveness after 2 weeks. The pyrethroids, cypermethrin and permethrin, were more toxic to T. castaneum than to C. ferrugineus. For malathion and pirimiphos-methyl, percentage knockdown of the insects following exposure for 24 h was similar to percentage mortality after a 3-day recovery period; for cypermethrin and permethrin under the same conditions, knockdown was consistently greater than mortality. Cypermethrin at 8 ppm on wheat gave 90% knockdown of T. castaneum after 1 year of storage. Pirimiphos-methyl gave nearly 100% control of both species for 9 months at 4 ppm and 11 months at 8 ppm, and of the grain mite Acarus siro (L.) for at least 4 weeks at 8 ppm. Seed germination did not change during 1 year of storage; the levels of Penicillium spp. infection observed were much greater (about 60%) on wheat treated with pirimiphos-methyl (2, 4, 8 ppm) or cypermethrin (2 ppm) than with malathion or permethrin.