Baseline monitoring of chlorfenapyr and alpha-cypermethrin-based interceptor G2 long-lasting insecticidal net components against the tropical bed bug (Hemiptera: Cimicidae): implications for non-target pest control in Africa

The interceptor G2, a newly recommended dual-ingredient long-lasting insecticidal net (LLIN) by the World Health Organization (WHO), contains chlorfenapyr (pyrrole) and alpha-cypermethrin (pyrethroid), demonstrating efficacy against malaria vectors in Africa. Despite the extensive deployment of LLINs for malaria vector control across sub-Saharan Africa, there is limited understanding of their impact on non-target hematophagous pests sharing similar ecological habitats. Through contact bioassays, a total of 28 Cimex hemipterus (F.) strains from 7 regions in Ghana were tested against chlorfenapyr, alphacypermethrin, and a combined mixture at recommended label rate of Interceptor G2. We found that chlorfenapyr showed significantly lower survival times and higher mortality within 48 h post-exposure (24/28 strains ≥ 80% mortality) compared to alpha-cypermethrin (4/22 strains ≥ 80% mortality) when tested independently, indicating widespread resistance to pyrethroids. The chlorfenapyr/alpha-cypermethrin combination had comparable effectiveness (23/24 strains ≥ 80% mortality) to chlorfenapyr, and synergistic interactions between the active ingredients became more apparent at 48 h post-exposure. Late instar nymphs displayed a similar susceptibility trend to adults, but survival times were variable and often longer in the nymphs than adults. These results suggest that the deployment of Interceptor G2 nets may provide incidental but beneficial control of bed bug populations, including those resistant to pyrethroids. However, prolonged exposure to chlorfenapyr may result in resistance to chlorfenapyr in the future. This work sets a baseline for monitoring the risk and understanding the evolution of insecticide resistance in bed bugs especially to chlorfenapyr under selective pressure from future widespread use of Interceptor G2 in Africa.