Testing a pyriproxyfen auto-dissemination station attractive to gravid Anopheles gambiae sensu stricto for the development of novel attract-and-kill strategies for malaria vector control

Abstract

Background Larval source management is an effective supplementary tool for malaria vector control although it is not used widely in sub-Saharan Africa. This study explored whether an attract-and-kill strategy could contaminate gravid Anopheles gambiae sensu stricto with the insect growth regulator, pyriproxyfen, at a bait-station, for dissemination to larval habitats. Methods A bait-station comprising an artificial pond, containing water was treated with 20 ppm cedrol, an oviposition attractant, was covered with pyriproxfen-treated netting. Three identical semi-field cages were used to assess the potential of gravid Anopheles gambiae sensu stricto to transfer pyriproxyfen from the bait-station to three open ponds. Gravid females were released in the test and one of the control cages that had no pyriproxyfen on its bait-station. No mosquitoes were released in the third cage with a pyriproxyfen-treated station. Transfer of pyriproxyfen to open ponds was assessed by monitoring emergence of late instar insectary-reared An. gambiae sensu stricto larvae introduced into the open ponds. Liquid chromatography-mass spectrometry was used to quantify the amount of pyriproxyfen carried by a mosquito and the amount transferred to water. Results 86% (95% CI 81-89%) of larvae introduced into the open ponds in the two control cages developed into adults. Transfer of pyriproxyfen to the test cage depended on the distance of the pond from the bait-station. While only 25% (95% CI 22-29%) adult emergence was observed in larvae introduced into ponds 4.4 m from the bait-station, the emergence rates increased to 92% (95% CI 89-94%) in larvae introduced in ponds 10.3 m away. Each mosquito was contaminated with 112 µg (95% CI 93-123 µg) pyriproxyfen, whilst 230 ng/L (95% CI 180-290 ng/L) was transferred by a single female to 100 ml of water. Conclusions Pyriproxyfen was auto-disseminated by gravid females from attractive bait-stations, but mainly to aquatic habitats near the bait station. To make this approach feasible for malaria vector control, stronger attractants and better pyriproxyfen delivery systems are needed.