Seasonal Escalation of Organophosphorus and Carbamate Resistance inAnopheles albimanusby Agricultural Sprays

Abstract

Levels of resistance to organophosphorus and carbamate insecticides in larvae of Anopheles albimanus Wiedemann within the cotton-growing area of E1 Salvador were studied over a 2-year period, 1970–72. Sampling was done in June and February of each year, i.e., at the beginning and end of the cotton-spraying season. Resistance to parathion, methyl parathion, malathion, fenitrothion, carbaryl, and propoxur was found to rise during the spray period and to decline somewhat during the nonspray period, revealing an escalatory pattern which attained remarkably high levels by February 1972. Organophosphorus resistance manifested a lower degree of decline than carbamate resistance under both laboratory and field conditions during the nonspraying season. This decline was attributed to unequal integration of the respective resistance genes with fitness factors. Resistance to malathion, propoxur, and fenitrothion in A. albimanus in Central America emphasizes the need for coordination of pest-control efforts in agriculture and public health. Since these insecticides are considered the most promising as substitutes for DDT and dieldrin in malaria eradication, it is obvious that their prior and extensive use in agriculture in malarious areas tends to jeopardize their subsequent usefulness against anopheline mosquitoes.