Sterilising effects of pyriproxyfen on Anopheles arabiensis and its potential use in malaria control

Abstract

BackgroundInsecticide resistance poses a major threat to current vector control campaigns. Insecticides with novel modes of action are therefore in high demand. Pyriproxyfen (PPF), a conventional mosquito pupacide, has a unique mode of action that also sterilises adult mosquitoes (unable to produce viable offspring) upon direct contact. However, the timing of PPF exposure in relation to when mosquitoes take a blood meal has an important impact on that sterilisation. This study investigated the relationship between different blood feeding and PPF exposure timings to determine the potential of PPF sterilisation in controlling Anopheles arabiensis.MethodsFour treatment regimens were investigated: blood fed three days before PPF exposure (A), blood fed one day before PPF exposure (B), blood fed one day after PPF exposure (C) and blood fed three days after PPF exposure (D) for their impact on egg laying (fecundity) and the production of viable offspring (fertility), while the impact of PPF exposure on mosquito survival was investigated in the absence of a blood meal. All regimens and the survival study exposed mosquitoes to PPF via the bottle assay at 3 mg AI/m2 for 30 minutes.ResultsFemale mosquitoes that blood-fed one day prior to PPF exposure (regimen B), produced no viable offspring during that gonotrophic cycle (100% reduction in fertility). All other treatments had no significant effect. The observed reductions in fecundity and fertility were caused by the retention of eggs (97% of eggs retained, i.e. produced in the ovaries but not laid, in regimen B, p = 0.0004). Some of these retained eggs were deformed in shape. PPF exposure on mosquito survival in the absence of a blood meal was found to have no effect.ConclusionsThe results presented here suggest that sterilising adult malaria vectors using PPF could form part of a malaria control strategy, taking advantage of the lack of reported resistance to PPF in mosquitoes and its unique mode of action. We propose that targeting resting mosquitoes, which are highly susceptible to PPF at low doses, is the optimal direction for developing this control tool.

Using UPLC–MS/MS to Evaluate the Dissemination of Pyriproxyfen by Aedes Mosquitoes to Combat Cryptic Larval Habitats after Source Reduction in Kaohsiung in Southern Taiwan

“…Third, this study used commercial, solution-based PPF at a low concentration (0.01%) for application. Previous studies used a granular formulation of PPF (Sumilarv 0.5G), and pretreatment was often required, such as pulverization and grinding into powder [11,13,15] or agitation in organic solvents [22,28,29]. The ULV spray commonly used the 10% PPF concentrate (NyGuard ® IGR Concentrate) for application [24,26].…”

Male mosquitoes as vehicles for insecticide

“…This late-acting effect can be advantageous in mitigating densitydependent effects, which can offset the impact of earlier-acting compounds [41,42]. 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].…”

Chemosterilants for Control of Insects and Insect Vectors of Disease

“…[49] In a separate study of A. arabiensis , total sterility was observed upon 30 min exposure to pyriproxyfen 24 h after blood feeding but not 72 h prior to, or 24–72 h after, blood feeding. [50] Deploying pyriproxyfen-dusted cloths within test huts, a 96% reduction in adult production vs. control was observed in semi-field conditions. [51] …”