The susceptibility to insecticides of disease-carrying mosquitos in Fiji.

The larvae and adults of five species of vector mosquitos in Fiji have been tested for susceptibility to chlorinated hydrocarbon insecticides by standard techniques. Four species of Aëdes, three of them endemic to the South Pacific, gave results not differing greatly from those found for members of the genus in other countries. Culex fatigans Weid was unusually susceptible as a larva but as an adult was normal.A strain of A. pseudoscutellaris Theo. resistant to DDT as a larva was readily obtained by selective pressure, the LC(50) being increased to some 2000 times that of a susceptible wild strain. There was no cross-resistance to BHC or dieldrin but adults of this strain showed a slightly increased tolerance to DDT. It is suggested that inheritance is monofactorial, that the gene is present at a low frequency in wild populations and is favoured by domestication or urban conditions. There are indications of physiological differences between resistant and susceptible individuals.