Recent experiments on possible resistance to DDT by Anopheles albimanus in Panama.

Following the observation of a change in the effectiveness of DDT residual house-spraying for Anopheles albimanus control at two experimental villages on the Chagres River in Panama, laboratory experiments were made to measure possible physiological resistance in this mosquito.Blood-engorged albimanus from (a) a stock colony which had never had contact with DDT or any other chlorinated-hydrocarbon insecticide, (b) a stock-colony strain which had been exposed to DDT for more than 70 generations, and (c) two villages where 5% DDT in kerosene had been frequently applied, were exposed for 12 minutes to 0.5% p,p'-DDT in mineral oil.The results showed that both the wild albimanus and the exposed stock-colony strain had essentially the same susceptibility to DDT as the unexposed stock-colony mosquitos. Any difference in the effectiveness of the insecticide for albimanus is therefore considered to be due to a behaviour change rather than to a change in the intrinsic toxicity of DDT for this mosquito.