Assessing the additional effects of piperonyl butoxide (PBO) exposure on Anopheles mosquitoes

Insecticide treated nets (ITNs) remain one the frontline tool in malaria control in Africa. The synergist piperonyl butoxide (PBO) has been incorporated into ITNs to combat pyrethroid resistance and these pyrethroid-PBO ITNs are now in widespread use across Africa. PBO is known to inhibit the degradation of pyrethroids and other insecticide classes, but little is known about other biological or behavioural effects of PBO exposure. This work assessed the impact of PBO on Anopheles gambiae s.l. male longevity as well as female host-seeking and blood feeding behaviours using laboratory assays. PBO had an immediate impact on blood feeding of female An. gambiae s.l. whereas the effect was not observed 24h post-exposure. Kaplan-Meier survival curves showed a significant difference in mosquito longevity post-exposure to PBO with male mosquitoes living nearly three times as long if exposed to control papers compared to PBO. In olfactometer assays, after exposure to control papers, control mosquitoes were significantly more attracted to host-odours, however, this attraction preference was reversed following PBO exposure. This study shows that in experimental assays, PBO has other effects on mosquito physiology and this is likely to contribute to the impact of pyrethroid - PBO ITNs in vector control programmes.