Transfluthrin Eave-Positioned Targeted Insecticide (EPTI) Reduces Human Landing Rate of Pyrethroid Resistant and Susceptible Malaria Vectors in a Semi-Field Simulated Peridomestic Space

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Abstract Introduction: Volatile pyrethroids (VPs) are proven to reduce human–vector contact for mosquito vectors. With increasing resistance to pyrethroids in mosquitoes, the efficacy of VPs such as transfluthrin may be compromised. Therefore, experiments were conducted to determine if the efficacy of transfluthrin eave-positioned targeted insecticide (EPTI) depends on the resistance status of malaria vectors.Methods: Ribbons treated with 5.25 g transfluthrin or untreated controls were used around the eaves of an experimental hut as EPTI inside a semi-field system. Mosquito strains with different levels of pyrethroid resistance were released simultaneously, recaptured by means of human landing catches (HLCs) conducted 2.5 m outside the hut, and monitored for 24-hour mortality. Technical-grade (TG) transfluthrin was used, followed by emulsifiable concentrate (EC) transfluthrin and additional mosquito strains. Generalised linear mixed models with binomial distribution were used to determine the impact of transfluthrin and mosquito strain on mosquito landing rates and 24-hour mortality. Results: A significant interaction between strain and treatment indicated that the effect of the transfluthrin EPTI varied between three strains under investigation (P < 0.001). Whether TG or EC, EPTI significantly reduced the odds of landing of pyrethroid-susceptible mosquitoes Anopheles gambiae (Ifakara) and An. gambiae (Kisumu) and of pyrethroid-resistant mosquitoes An. arabiensis (Mbita), An. gambiae Kisumu knockdown-resistant (Kisumu-kdr) and An. arabiensis (Kingani), with PE > 40% for all strains (P < 0.001). In the control, An. gambiae mosquitoes were more likely to land than An. arabiensis (P < 0.05). Conclusions: This study confirms that the efficacy of EPTI was not dependent on mosquito pyrethroid resistance status. However, it remains unclear whether resistance to pyrethroids undermines the efficacy of transfluthrin for bite prevention. It is important to consider mosquito anthropophagy, strain, years of colonisation and fitness when assessing vector control interventions. Overall, these findings suggest that transfluthrin-treated EPTI could be useful in areas with highly pyrethroid-resistant mosquitoes. At this dosage, transfluthrin EPTI cannot be used to kill exposed mosquitoes.

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