A control experiment with chemosterilized male Cutex pipiens fatigans Wied. in a village near Delhi surrounded by a breedmg-free zone

A strain of Culex quinquefasciatus with European cytoplasm and Indian chromosomes, including a male-linked translocation, was reared and males were released in two villages near Delhi which were surrounded by a 3-km wide zone kept free of mosquito production by conventional larvicides. 5000--40,(XX) males were released per day per village and this produced very high ratios of released to wild males. As a result of matings of wild females to released males up to 68% of the egg rafts laid in the villages showed cytoplasmic incompatibility (sterility) but, despite continued releases, the sterility rate plateaued and eventually declined. This can be partly explained by a decline in emergence of virgin females in the villages but it was concluded that immigration of already inseminated females must also have had an important influence. The trend in the wild adult female populations and the breeding in the release villages in comparison with untreated villages indicated that the releases produced partial population suppression.

The competitiveness carrying males of three genetic control systems for Aedes aegypti (L.), viz. chemosterilized males, double translocation heterozygote males (TIT3) and distorter double translocation heterozygote males (DT1T3), released into a natural population in the Delhi metropolitanxarea was evaluated using a method based on the principle of release and recapture of marked females. Chemosterilized males and DTIT3 males showed approximately normal competitiveness in the field which is similar to the results obtained from laboratory and field cage experiments. The TIT3 males were found to have reduced competitiveness both in the field and laboratory cage tests, in contrast to previously reported results with unmarked T1T3 males in field cages. The cause of this reduction in competitiveness was not clear.