Pyriproxyfen for mosquito control: female sterilization or horizontal transfer to oviposition substrates by Anopheles gambiae sensu stricto and Culex quinquefasciatus

Abstract

BackgroundThe use of gravid mosquitoes as vehicles to auto-disseminate larvicides was recently demonstrated for the transfer of pyriproxyfen (PPF) by container-breeding Aedes mosquitoes and presents an appealing idea to explore for other disease vectors. The success of this approach depends on the female’s behaviour, the time of exposure and the amount of PPF that can be carried by an individual. We explore the effect of PPF exposure at seven time points around blood feeding on individual Anopheles gambiae sensu stricto and Culex quinquefasciatus fecundity and ability to transfer in laboratory assays.MethodMosquitoes were exposed to 2.6 mg PPF per m2 at 48, 24 and 0.5 hours before and after a blood meal and on the day of egg-laying. The proportion of exposed females (N = 80-100) laying eggs, the number of eggs laid and hatched was studied. Transfer of PPF to oviposition cups was assessed by introducing 10 late instar insectary-reared An. gambiae s.s. larvae into all the cups and monitored for adult emergence inhibition.ResultsExposure to PPF between 24 hours before and after a blood meal had significant sterilizing effects: females of both species were 6 times less likely (Odds ratio (OR) 0.16, 95% confidence interval (CI) 0.10-0.26) to lay eggs than unexposed females. Of the few eggs laid, the odds of an egg hatching was reduced 17 times (OR 0.06, 95% CI 0.04-0.08) in Anopheles but only 1.2 times (OR 0.82, 95% CI 0.73-0.93) in Culex. Adult emergence inhibition from larvae introduced in the oviposition cups was observed only from cups in which eggs were laid. When females were exposed to PPF close to egg laying they transferred enough PPF to reduce emergence by 65-71% (95% CI 62-74%).ConclusionPPF exposure within a day before and after blood feeding affects egg-development in An. gambiae s.s. and Cx. quinquefasciatus and presents a promising opportunity for integrated control of vectors and nuisance mosquitoes. However, sterilized females are unlikely to visit an oviposition site and therefore do not transfer lethal concentrations of PPF to aquatic habitats. This suggests that for successful auto-dissemination the optimum contamination time is close to oviposition.

Targeting a Hidden Enemy: Pyriproxyfen Autodissemination Strategy for the Control of the Container Mosquito Aedes albopictus in Cryptic Habitats

“…Similarly, the ability of autodissemination to transfer lethal concentrations of insecticides has been successfully demonstrated in the laboratory and the field for Ae . albopictus and other mosquito vectors [12,25–29]. Previous studies, however, have used only open cups to assess autodissemination efficacy and did not examine efficacy in cryptic habitats.…”

Male mosquitoes as vehicles for insecticide

“…An additional feature of PPF that may be examined in future ADAM-related work are its effects on female fertility and male spermiogenesis [23,[43][44][45]. Specifically, PPF contamination of females can reduce fertility of females and males, which can negatively impact the population in addition to the pupacidal effect of PPF [46].…”

Evaluating the sterilizing effect of pyriproxyfen treated mosquito nets against Anopheles gambiae at different blood-feeding intervals

“…However, Koama et al showed that a single exposure to pyriproxyfen treated netting reduced the number of eggs laid by >75% over three gonotrophic cycles when the first blood-meal was shortly after exposure (Koama et al, 2015). It has been shown that pyriproxyfen is a potent inhibitor of pupal eclosion at very low concentrations and that adult mosquitoes can transfer pyriproxyfen to larval waters during oviposition (Mbare et al, 2014;Wang et al, 2014;Lwetoijera et al, 2014b). The impact of so-called autodissemination will depend on the dosage of pyriproxyfen remaining on tarsi by the time of oviposition and the volume of water in breeding sites.…”

“…Mbare et al conducted similar trials with An. gambiae and showed that exposure up to 24 h before or after blood-feeding resulted in a moderate reduction in egg laying of between 56 and 62% (Mbare et al, 2014). Exposure to pyriproxyfen 48 h before blood-feeding had only a 32% reduction in oviposition, while exposure 48 or 72 h after blood-feeding had no impact (Mbare et al, 2014).…”