Populations of A. albimanus in the cotton growing belt of Central America manifest a mosaic pattern of tolerance to organophosphorus and carbamate insecticides. In certain localities especially in the coastal area of the Departments of La Libertad and La Paz, El Salvador, and in the Sebaco Valley, Nicaragua, moderate to high resistance levels to a number of organophosphates and carbamates are present in larvae, and this resistance extends to the adult stage as well. There appears to be a correlation between intensive chemical pest control operations, especially on cotton, and the incidence of resistance to organophosphorus and carbamate insecticides in A. albimanus, possibly as a result of indirect selection due to contamination of mosquito breeding habitats.
Higher resistance in the Department of La Paz, El Salvador, coincides with higher density cotton cultivation, larger than average cotton acreage per grower, greater proportion of aerial applications of insecticides than in other cotton growing Departments of the country, and possibly presence of a larger acreage of rice. The level of resistance fluctuates seasonally, being lower at the beginning and higher at the end of the cotton spraying season.
Field populations from the Department of La Libertad, El Salvador, were found to respond readily to selection pressure by propoxur in the laboratory, developing resistance to this compound and cross resistance to carbaryl, parathion, methyl parathion, malathion and fenitrothion. It is not unlikely that populations of the species from other areas within the cotton growing belt will respond similarly to selection pressure.