Cross-resistance to Bacillus sphaericus strains in Culex quinquefasciatus resistant to B. sphaericus 1593M.

Bacillus sphaericus 1593M resistant larvae of Culex quinquefasciatus were reared in the laboratory since 1995. Resistance in the larvae was monitored by subjecting selection pressure using B. sphaericus 1593M at every generation. Bioassays were conducted with different strains of B. sphaericus (Bs 2297, Bs 2362 and Bs IAB 59) and confirmed cross-resistance in the present study. The level ranged between 27.3 to 18.2 fold in comparison with susceptible larvae. But Bacillus thuringiensis var israelensis strains (Bti PG14 and Bti 426) did not show any cross-resistance in the larvae and it emphasized a need to study the mode of action of B. sphaericus toxin that induces cross-resistance in the larval strain.

Space-spraying with malathion as a supplementary measure for operational malaria control.

Entomological studies showed that due to outdoor resting by the vector Anopheles culicifacies as well as poor spray coverage, indoor residual spraying with malathion was ineffective in malarious villages of the Thenpennai riverine tract in Tamil Nadu. Over a 4 yr period during which residual spraying was supplemented with ground applications of malathion space spraying, the slide positivity among patients with fever fell from 21.04 to 1.1 per cent. In mass blood surveys 0.7 per cent persons surveyed at the beginning of the study were positive for the malarial parasite, but no positives were detected in the last survey, in 1984. There was a rising trend in malaria incidence in riverine villages outside the programme.