Susceptibility to organophosphate insecticides in larval Aedes albopictus

Larvae of 26 strains of Aedes albopictus were tested for susceptibility to 5 organophosphate insecticides. The recently collected geographic strains included 13 from the USA, 5 from Brazil, 3 from Southeast Asia and 5 from Japan. The greatest amount of variability was seen among U.S. populations, ranging from quite susceptible to potentially resistant. Brazilian samples were generally quite susceptible to all insecticides tested. Three Japanese strains showed tolerance or low level resistance to fenitrothion (2X, 3X and 8X), as did 2 U.S. strains (3X and 5X). Two U.S. strains showed tolerance to malathion (3X and 4X), while one strain from Chicago, Illinois, showed low level resistance (22X). Selection for resistance to malathion in a laboratory strain composed of multiple U.S. geographic strains resulted in a resistance ratio of 21X after 6 generations of selection.