Evaluating the transstadial effects of Bacillus velezensis and pyriproxyfen, alone and in combination, on fitness-related traits of Culex quinquefasciatus.

BACKGROUND

Lethal and sublethal effects of exposure to chemical and microbial agents can alter many mosquito life history traits and provide opportunities for integrated mosquito control strategies to reduce the risk of disease transmission. The insect growth regulator pyriproxyfen (PPF) disrupts metamorphosis by mimicking juvenile hormone, which primarily targets mosquitoes during the pupal-adult transformation. Biological agents like Bacillus velezensis (Bv) show larvicidal activity against mosquitoes, which can work in concert with the mode of action of PPF to enhance overall mosquito population suppression.

METHODS

This study investigated how PPF and Bv alone or in combination impact Culex quinquefasciatus performance and population recruitment by assessing both lethal (adult emergence as a proxy for overall immature mortality) and sublethal effects on fitness-related traits (lifespan and reproductive outputs). Experimental bioassays were conducted under laboratory standard conditions to determine mortality, development duration, lifespan, size, and fecundity.

RESULTS

Both agents independently reduced adult mosquito emergence, with the combination treatment producing the greatest overall reduction. When applied together, PPF and Bv significantly shortened adult female lifespan and reduced fecundity and hatching success of the offspring compared to individual treatments and the control. The combined treatment produced the most pronounced reductions across these life-history traits, indicating an additive effect.

CONCLUSIONS

These findings highlight the potential of integrating PPF with a natural bacterial biocontrol agent through strong lethal and sublethal effects across multiple life stages of Cx. quinquefasciatus, including reduced adult lifespan and reproduction. Such an integrated approach can enhance the effectiveness of vector control while providing a sustainable and promising strategy to lower the risk of mosquito-borne disease transmission.