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PubMed1954

Evidence of the development of resistance to DDT by Anopheles sacharovi in the Levant.

Resting A. sacharovi reappeared in the autumn of 1953 on some walls in certain localities of north Lebanon which had been treated with DDT during the preceding 18 months. Tests were made on the spot with female mosquitos having a known minimum contact of 5 to 15 minutes with DDT residues, chemically estimated at 0.1-2.0 g/m(2). The resulting mortality within 48 hours (corrected to allow for deaths observed in the control runs) was 60.1% and 45.1% according to the technique used, compared with 100% to 83% within 24 hours in similar tests on the same strains some months earlier. The specimens which died had contacted a lower average residue than those which survived, and the latter included some exposed for 15 minutes to 1.8 g/m(2).The theory is put forward that selection for DDT resistance (a phenomenon already known in A. sacharovi elsewhere) is probably occurring in these Lebanese strains after only two seasons of regular spraying. The prevalence of sooty surfaces, which absorb DDT, is considered to be a factor contributing to selection by reducing residues to a level within the "critical range" for the non-resistant mosquitos. Attention is drawn to work which indicates a similar response to DDT in strains of A. gambiae and A. funestus in Africa.The importance is stressed of planning antimalaria campaigns in a way that will either prevent selection for resistance or will permit counteraction of it before it can lead to large wastage of public money.

Africa↗
PubMed1954

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.

Animals↗