Determination of the residual efficacy of broflanilide (VECTRON™ T500) insecticide for indoor residual spraying in a semi-field setting in Ethiopia.

Background: The rotational use of insecticides with diverse modes of action in indoor residual spraying (IRS) is pivotal for enhancing malaria vector control and addressing insecticide resistance. A key factor in national malaria vector control/elimination programmes is the rate at which these insecticides decay. VECTRON™ T500, with broflanilide as its active ingredient, is a recently developed candidate insecticide formulation which has shown promising results in certain phase II experimental hut trials. However, its residual efficacy across different settings has not been thoroughly investigated. This study evaluated the efficacy of VECTRON™ T500 on various wall surfaces (mud, dung, paint, and cement) and assessed its decay rates over time in Ethiopia.

Methods: Insectary-reared Anopheles arabiensis Sekoru strain mosquitoes were used to evaluate the residual efficacy of VECTRON™ T500. Female mosquitoes, aged three to five days were used for the bioassays. Seven 'tukul' type test huts, each hut with a distinct wall type (mud, dung, painted, and cemented) were used for the study. Three huts received VECTRON™ T500; three huts were sprayed with Actellic 300CS, and one hut served as a negative control (sprayed with water only).

Results: VECTRON™ T500 induced over 80% mortality across all wall surface types throughout the entire nine-month study period. In contrast, Actellic^® 300CS achieved over 80% mortality for six months, except on dung wall surfaces, after which its efficacy declined sharply below 80%.

Conclusion: Overall, the mortality rates achieved with VECTRON™ T500 extended up to nine months across all treated wall surface types, outperforming Actellic^® 300CS. This could make VECTRON™ T500 a promising candidate insecticide formulation for use in IRS in malaria-endemic countries such as Ethiopia.