Impact of pyriproxyfen on the reproduction of pyrethroid-resistant Anopheles gambiae s.l. populations in benin: what implications for vector control?

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BACKGROUND: The efficacy of LLINs is compromised by the emergence of pyrethroid resistance in malaria vectors. New insecticides that target other sites of action in the mosquito, including pyriproxyfen (PPF), are needed to maintain this efficacy. METHODS: Various populations of An. gambiae s.l. collected from April to November 2022 in 4 Beninese communes and the susceptible strain (Kisumu) were used to assess their susceptibility to PPF via CDC bottle tests and to assess the bioefficacy of Royal guard® (RG) alpha-cypermethrin + pyriproxyfen-impregnated nets via WHO cone tests. Molecular analyses were carried out to observe the frequency of resistance genes, and the oviposition and oviposition inhibition rates of these different populations to PPF were calculated. Ovaries of An. gambiae s.l. from Bohicon and Lokossa exposed to RG were dissected, and egg development was examined via Christopher stages to determine the fertility status of the mosquitoes. RESULTS: Across all analyzed An. gambiae s.l. populations, the mean kdr allele frequency was approximately 85.08%. The rate of oviposition inhibition by PPF was approximately 98% for the wild populations of Djougou and Malanville and for the susceptible strain of An. gambiae Kisumu. In the cone test, RG showed optimal efficacy with the susceptible Kisumu strain. However, the mortality rate of wild populations with RG ranged from 12.5% [95% CI: 5.18–24.07] to 32.08% [95% CI: 19.92–46.32], whereas it varied between 0% [95% CI: 0–7] and 4% [95% CI: 4.9–14] with Interceptor®. All An. gambiae s.l. populations in Bohicon and Lokossa exposed to the RG net were infertile (100% [95% CI: 95.07–100]), whereas with Interceptor® and the untreated net, the majority had fully developed their eggs up to Christopher stage V. CONCLUSION: Under laboratory conditions, PPF had a considerable effect on mosquito reproduction, rendering all An. gambiae s.l. populations exposed to the insecticide and the RG net infertile.

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