Spatial Anopheles arabiensis (Diptera: Culicidae) insecticide resistance patterns across malaria-endemic regions of Botswana.

Background: Since the advent of the Green Revolution, pesticides have played an important role in the global management of invertebrate pests including vector mosquitoes. Despite optimal efficacy, insects often display insensitivity to synthetic insecticides owing to prolonged exposure that may select for resistance development. Such insecticide insensitivity may regress national and regional coordination in mosquito vector management and indeed malaria control. In Botswana, prolonged use of synthetic insecticides against malaria vectors have been practiced without monitoring of targeted mosquito species susceptibility status.

Methods: Here, susceptibility status of a malaria vector (Anopheles arabiensis), was assessed against World Health Organization-recommended insecticides, across three malaria endemic districts. Adult virgin female mosquitoes (2-5 days old) emerging from wild-collected larvae were exposed to standardized insecticide-impregnated papers with discriminating doses.

Results: The results showed resistance dynamics were variable in space, presumably as a result of spatial differences in insecticide use across malaria endemic districts and the types of insecticides used in the country. Overall, there was a reduced susceptibility of An. arabiensis for the pyrethroid lambda-cyhalothrin and for dichloro diphenyl trichloroethane [DDT], which have similar modes of action and have been used in the country for many years. The Okavango district exhibited the greatest reduction in susceptibility, followed by Ngamiland and then Bobirwa, reflective of national intervention strategy spraying intensities. Vector mosquitoes were, however, highly susceptible to carbamates and organophosphates irrespective of region.

Conclusions: These results provide important findings of vector susceptibility to insecticides recommended for vector control. The results highlight the need to implement insecticide application regimes that more effectively including regionally integrated resistance management strategies for effective malaria control and elimination.