Assessment of methoxy-DDT as a residual spray against mosquitoes in verandahtrap huts at Magugu, Tanzania

Abstract

The effects of residual sprays of methoxy-DDT wettable powder at 2 g/m2 on the mortality and behaviour of Anopheles gambiae Giles, Mansonia uniformis (Theo.) and Culex pipiens fatigans Wied. females were investigated in four verandah-trap huts, one of which was used as control. The overall mortality of no species ever exceeded 29%, and no consistent deterrent effect on entry was demonstrated. The proportions of mosquitoes in the exit traps were, for A. gambiae 80–90% in treated huts and 29–70% in the control, for M. uniformis 90–100% in treated and control huts, and for C. p. fatigans 26–84% in treated huts and 38–66% in the control. There were more unfed mosquitoes of all three species in the treated huts than in the control, for A. gambiae 35–64% and 10–53%, respectively, for M. uniformis 38–84% and 35–64%, respectively, and for C. p. fatigans 22–58% and 21–43%, respectively. Bioassays with wild-caught A. gambiae exposed to the treated surfaces for one hour, showed that the deposits remained highly toxic for 16 weeks on grass, six weeks on iron and two weeks, or less, on mud.

Trials of residual sprays of Mobam and carbaryl against mosquitoes in verandah-trap huts at Taveta, Kenya

“…Both compounds caused a slight increase in the egress of blood-feds, but neither was as repellent as DDT (Smith & Webley, 1969) or methoxy-DDT (Hudson, 1971). Neither compound had the deterrent effect of DDT or of mosquito coils containing pyrethrins (Hudson, 1971). Both compounds caused a slight inhibition of feeding, but not nearly as much as did tetramethrin (Smith & Chabeda, 1969) or mosquito coils.…”

“…In contrast to some of the other compounds which have been tried in verandahtrap huts, neither Mobam nor carbaryl greatly modified the house-resting or feeding behaviour of A. gambiae. Both compounds caused a slight increase in the egress of blood-feds, but neither was as repellent as DDT (Smith & Webley, 1969) or methoxy-DDT (Hudson, 1971). Neither compound had the deterrent effect of DDT or of mosquito coils containing pyrethrins (Hudson, 1971).…”

“…The carbaryl appeared to be slightly repellent to A. gambiae, but the repellency indices were never more 1-18. For comparison, Smith & Webley (1969) found repellency indices of 1-35-2-76 for DDT, and Hudson (1971) repellency indices of 1-35-3-81 for methoxy-DDT.…”