Influence of testing modality on bioefficacy for the evaluation of Interceptor ® G2 mosquito nets to combat malaria mosquitoes in Tanzania

Insecticide-treated net (ITN) durability is evaluated using longitudinal bioefficacy and fabric integrity sampling post-distribution. Interceptor G2 was developed for resistance management and contains two adulticides: alpha-cypermethrin and chlorfenapyr; it is a pro-insecticide that is metabolized into its active form by mosquito-detoxifying enzymes and may be enhanced when the mosquito is physiologically active. To elucidate the impact of bioassay modality, mosquito exposures of the alphacypermethrin ITN Interceptor and dual adulticide Interceptor G2 were investigated. This study evaluated the performance of Interceptor G2 compared to Interceptor against local strains of mosquitoes in Tanzania. Unwashed and 20× times washed nets were tested. Efficacy of ITNs was measured by four bioassay types: (1) World Health Organisation (WHO) cone test (cone), (2) WHO tunnel test (tunnel), (3) Ifakara ambient chamber test (I-ACT) and (4) the WHO gold standard experimental hut test (hut). Hut tests were conducted against free-flying wild pyrethroid metabolically resistant Anopheles arabiensis and Culex quinquefasciatus. Cone, tunnel and I-ACT bioassays used laboratory-reared metabolically resistant An. arabiensis and Cx. quinquefasciatus and pyrethroid susceptible Anopheles gambiae sensu stricto and Aedes aegypti. Against resistant strains, superiority of Interceptor G2 over Interceptor was observed in all "free-flying bioassays". In cone tests (which restrict mosquito flight), superiority of Interceptor over Interceptor G2 was recorded. Mortality of unwashed Interceptor G2 among An. arabiensis was lowest in hut tests at 42.9% (95% CI: 37.3-48.5), although this increased to 66.7% (95% CI: 47.1-86.3) by blocking hut exit traps so mosquitoes presumably increased frequencies of contact with ITNs. Higher odds of mortality were consistently observed in Interceptor G2 compared to Interceptor in "free-flying" bioassays using An. arabiensis: tunnel (OR = 1.42 [95% CI:1.19-1.70], p