ANOPHELES ARABIENSIS AND ANOPHELES-GAMBIAE CHROMOSOMAL INVERSION POLYMORPHISM, FEEDING AND RESTING BEHAVIOR IN RELATION TO INSECTICIDE HOUSE-SPRAYING IN TANZANIA

Differential responses of the mosquitoes Anopheles arabiensis and An.g ambiae sensu stricto to house-spraying with DDT or lambda-cyhalothrin were evaluated in relation to chromosomal inversion polymorphism, feed ing and resting behaviour of these malaria vectors in Tanzania. Blood- fed mosquitoes from pit traps outdoors, exit traps on windows and indo or-resting catches were identified cytogenetically and the chromosomal inversion frequencies compared between samples and species. Their out door-resting behaviour was assessed by a mark-release-recapture experi ment and by determining the proportion of freshly blood-fed individual s in exit traps. The source of bloodmeals was analysed by an ELISA met hod. Endophagic females of An.arabiensis were more likely than those o f An.gambiae to exit from a house on the night of blood-feeding. Only in one out of three villages was there evidence that chromosomally dis tinct individuals within a species had different preferences for resti ng sites. There were indications, but not conclusive evidence, that mo squitoes caught indoors or outdoors had a tendency to return to the sa me type of resting site. In villages sprayed with either insecticide, the mean age of the vector populations was greatly reduced, compared w ith those in the unsprayed villages. An.arabiensis females exited from DDT sprayed houses after blood-feeding, whereas with lambda-cyhalothr in those exiting were mostly unfed and there was a decline in the huma n blood index. The excitorepellency of DDT was perceived as a disadvan tage, whereas lambda-cyhalothrin apparently had more impact on malaria transmission by An.arabiensis.