The sterilizing effect of pyriproxyfen on the malaria vector Anopheles gambiae: physiological impact on ovaries development

Abstract

Adult females An. gambiae were exposed in 3 min cone test to treated nets with PPF before or after they were blood fed. The effects of PPF on ovaries development, females oviposition and eggs hatching were assessed. Both unfed and fed mosquitoes exposed to PPF exhibited nearly complete inhibition of fecundity (70-100%) and fertility (90-100%). After females have been exposed once to PPF, the sterilizing effect on their fecundity was observed over 3 consecutive blood meals suggesting that PPF might have an irreversible sterilizing effect. Observation of the ovaries of exposed females to PPF under microscope revealed that the ovaries failed to develop even after several blood meals. The combination of PPF to pyrethroids on bednets could provide better malaria control tool and prevent the further development and spread of pyrethroid resistance in malaria vectors.

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

“…Koama et al demonstrated that exposure of An. gambiae to pyriproxyfen affected the rate at which ovarian follicles developed and resulted in malformed eggs that were less elongated and more spherical than the untreated controls (Koama et al, 2015). In this study it was shown that pyriproxyfen is equally effective against both nulliparous and parous mosquitoes.…”

“…The longer five day (120 h) interval between exposure and blood-feeding is an unrealistic scenario for a single gonotrophic cycle but the smaller reduction in reproductive rate indicates that the effects of pyriproxyfen are partially reversible through the action of metabolism or excretion. 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).…”

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

“…This study highlights a number of challenges that need to be taken into account for the development of an efficient auto-dissemination approach for African malaria vectors. Based on previous work we consider exposing gravid females to PPF the most effective way to ensure transfer to an aquatic habitat given that exposure earlier in a female's life has significant impact on her fertility and fecundity (33,34,36,46), lowering the females predisposition to visit an aquatic habitat. Attracting the gravid female is however more challenging than attracting a host-seeking or resting female, due to the scarcity of synthetic oviposition attractants (38,47,48).…”

Anopheline Reproductive Biology: Impacts on Vectorial Capacity and Potential Avenues for Malaria Control

“…Recent findings support the use of hormonal agonists as mosquito-control agents. Pyriproxyfen, an analog of the other major insect hormone juvenile hormone, produces both long-term sterility and life-shortening effects in Anopheles mosquitoes (Ohashi et al 2012;Harris et al 2013;Koama et al 2015), with promising results when applied to resting surfaces and bednets in semifield trials (Kawada et al 2014;Lwetoijera et al 2014). By combining sterilizing compounds with insecticides, mosquitoes resistant to the killing action of the insecticide will be unable to propagate the resistance traits to the next generation, therefore preventing selection and spread of insecticide-resistant alleles in the population, an idea coined as "negative cross resistance" (Fig.…”