Insecticide susceptibility in the South African malaria mosquito Anopheles arabiensis (Diptera: Culicidae)

Despite a century of insecticide use in agriculture and public health in South Africa, no insecticide susceptibility data exist for the malaria mosquito Anopheles arabiensis in South Africa. Biochemical assays and insecticide susceptibility tests were used to provide baseline data on DDT, deltamethrin, fenitrothion and propoxur susceptibility in field populations of An. arabiensis sampled from three areas, Mamfene, Thomo and Malahlapanga, South Africa, from March to May 1996. Mamfene and Thomo had been exposed for decades to heavy insecticide use for agricultural purposes and for malaria vector control, respectively. Malahlapanga had not been exposed to insecticide use and acted as a control. Mosquitoes from the three areas demonstrated complete susceptibility on standard testing, except for those from Thomo, which showed 75.1% mortality on one-hour exposure to 0.1% propoxur. The results of the biochemical assays showed no elevation of enzyme levels/activity for acetylcholinesterase, non-specific esterases or glutathion-s-transferase. Sensitivity to all the insecticides suggested no heterogeneity within the mosquito populations. This study provides the first insecticide susceptibility and biochemical data for An. arabiensis in South Africa and should serve as the baseline against which to compare chemical resistance when choosing insecticides for malaria vector control.