Identification of Elevated Esterase Activity in a Pyrethroid-Resistant Population of Anopheles albimanus Wiedemann

The standardized diagnostic World Health Organization (WHO) susceptibility test was used to evaluate DDT, permethrin, and deltamethrin on 2 laboratory colonized populations of An. albimanus from El Salvador (Santa Tecla) and Guatemala (El Semillero) and 2 field populations from northern (Corozal District) and southern (Toledo District), Belize. The Santa Tecla colony and Corozal field population were susceptible to all 3 compounds while the El Semillero colony showed resistance to all 3 compounds. The Toledo field population showed some resistance to DDT. The specific activity of esterase was measured in 5 populations of An. albimanus. These included Santa Tecla colony from El Salvador, El Semillero colony from Guatemala, Cayo population from Central Belize, Toledo population from Southern Belize, and Corozol population from Northern Belize. There was a 4 to 7 fold increase in the specific activity of esterase as measured by the hydrolysis of alpha- and beta-naphthylpropionate in the El Semillero colony compared to all the other populations, to include the TO population. This suggests that the development of physiological resistance to synthetic pyrethroids in the El Semillero colony from Guatemala may be related to increased esterase activity. Based on these overall results, permethrin and deltamethrin are potentially useful for An. albimanus control in Belize. The use of DDT in Toledo District seems effective, but warrants close monitoring in the future.