Sublethal effects of insecticides on the reproduction traits of insecticide-resistant Anopheles gambiae sensu lato mosquitoes from Tiassalé, Côte d’Ivoire

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Abstract Background Although exposure of Anopheles mosquitoes to insecticide-treated vector control tools is not always lethal, the sublethal effects of these insecticides on their life-history traits remain poorly explored. Therefore, this study examined the impact of sublethal exposure to broflanilide, chlorfenapyr and deltamethrin on longevity; blood meal acceptance; viable egg production; and the proportion of females with viable eggs in insecticide-resistant An. gambiae s.l. populations from Tiassalé, Côte d’Ivoire. Methods The sublethal effects of broflanilide, chlorfenapyr and deltamethrin were assessed on 3–5-day-old adult female An. gambie s.l. from the field collected Tiassalé strain (F 0 ), using the insecticide-susceptible Kisumu strain as reference, following standardized World Health Organization (WHO) bottle bioassay procedures. For each insecticide, the lethal dose causing 20% mortality (LD 20 ) was determined through dose–response analysis and then subsequently applied in treated bottles. Post-exposure, longevity, blood-feeding success, egg viability and the proportion of ovipositing females were recorded. Comparisons were made between the control and LD 20 treatment groups. Results Sublethal exposures produced distinct effects depending on both the mosquito strain and the insecticide type. Broflanilide significantly reduced longevity in the Tiassalé population ( P < 0.0001), whereas chlorfenapyr and deltamethrin had stronger effects on the Kisumu strain. Deltamethrin exposure notably impaired blood-feeding behaviour, reducing feeding success by 25.5% in Kisumu and 19.5% in Tiassalé. Reproductive parameters were also affected: both chlorfenapyr and broflanilide reduced viable egg production and the proportion of females producing viable eggs in both strains. In contrast, deltamethrin showed a more limited impact on reproduction. In the Tiassalé strain, the proportion of females producing viable eggs dropped to 41.5% following chlorfenapyr exposure, compared with 65.7% in unexposed individuals. Conclusions These findings demonstrate that sublethal doses of insecticides can adversely affect reproductive success and blood-feeding behaviour in both susceptible and resistant Anopheles mosquitoes, potentially reducing their vectorial capacity. This study underscores the need to systematically account for sublethal effects when evaluating insecticides in vector control programs, particularly in settings where resistance is widespread among malaria vectors.

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