Biochemical Systematics and Isozyme Expression in Insectiside Susceptible and Resistant Anopheles albimanus Wiedemann Populations

Isozymes of 6 test populations of Anopheles albimanus Wiedemann were compared using starch gel electrophoresis. Tests were performed on laboratory colonies from El Salvador, Guatemala, and Mexico, and 3 wild caught populations from Belize. From a total of 31 enzyme systems, 24 were consistently detected and 35 putative loci were scorable. Higher genetic variability was found in the 3 wild caught populations from Belize and the young colonies (2 years in the laboratory) from Guatemala and Mexico. Mean heterozygosity values of populations from Belize and the young colonies from Guatemala and Mexico ranged from 0.093 to 0.200, compared with 0.057 of the old colony (20 years in laboratory) from El Salvador. Detailed analyses showed all 6 populations of An. albimanus to be conspecific with minor instraspecific variations. Zymograms were compared among 6 test populations of An. albimanus, including a pyrethroid resistant colony from Guatemala (El Salvador). One locus of esterase, Est-3, was found to be diagnostic for separating susceptible and resistant populations. Since esterase was consistently elevated in the resistant population, we conclude that esterase may be specifically involved in the metabolic detoxification pathway in a pyrethroid resistant population. Due to regular agricultural use of organophosphate and carbamate insecticides in Guatemala, the elevated esterase activity in El Semillero colony also may be associated with these 2 compounds. Therefore, the elevated esterases in wild An. albimanus populations may be related to the exposure to organophosphate, carbamate, pyrethroids, or all 3 compounds, and may limit insecticide use against An. albimanus populations in parts of Central America.