Insecticide susceptibility in Anopheles pseudopunctipennis from Colombia: Comparison between bioassays and biochemical assays

Anopheles pseudopunctipennis, one of the primary vectors of malaria in the southwest of Colombia, was evaluated for susceptibility to the 3 major inse cticide groups (organophosphates, pyrethroids, and carbamates) by bioassay and biochemical assay. Larval populations, which were collected principally from irrigation channels in agricultural areas, where the intensity of ins ecticide use varied, were utilized to establish susceptibility for the Ist time in this species. The baselines for each population showed a range of b iological susceptibility to the insecticides evaluated, but overall no resi stance was detected according to standards established by the World Health Organization. The high sensitivity of biochemical microassays enabled the d etection of a small proportion of mosquitoes with higher levels of nonspeci fic esterases and mixed-function oxidases from 2 areas where agricultural a pplication of organophosphate and pyrethroid insecticides had been heavy. T hese differences were not sufficient to affect susceptibility as measured b y bioassay. No evidence of insensitive acetylcholinesterase was observed. A bsence of resistance in areas that have experienced heavy insecticide appli cation could be explained by genetic drift, by gene flow from areas without insecticide pressure, by manner of exposure to the insecticides, or by rec ent changes in agricultural activities that decreased insecticide use. Base line values were established that serve as provisional susceptibility thres holds for applying simple Centers for Disease Control and Prevention bioche mical assay and bioassay methods to larvae of this anopheline species.