Mosquito-mediated dissemination of pyriproxyfen from pyriproxyfen-based painted surfaces causes metamorphosis...

Technological advancements in insecticide-based formulations have emerged as a promising method to address the problem of mosquito control. However, the requirement for tools that could be impactful in targeting mosquito populations proliferating in the cryptic habitats is vital. The current study was performed to demonstrate the mosquito-vectored auto-dissemination of pyriproxyfen from the surfaces painted with pyriproxyfen-based paint. Paint formulation containing six different concentrations of pyriproxyfen (0.075%, 1%, 2%, 4%, 8%, and 16% in w/w) was applied on 15 cm × 15 cm pieces of metal, wood, plastic, and ceramic materials. Adult females (5-7 days old) were allowed to blood-feed and exposed to the treated material surfaces for 1 h using the WHO cone bioassay. After pyriproxyfen-based paint exposure, the females were transferred to small cages for egg laying. Liquid Chromatography - Tandem Mass Spectrometry (LC-MS/MS) was used to estimate the concentration of auto-disseminated pyriproxyfen in breeding water. The sterilisation effect of pyriproxyfen was observed through a reduction in fertility and fecundity, whereas the auto-dissemination impact was recorded through metamorphosis failure in the aquatic stage of Aedes aegypti kept in breeding water. There was a concentration-dependent change in the average number of eggs hatched (F = 5.8; p = 0.004); however, the average number of eggs laid was not concentration-dependent (F = 2.3; p = 0.1). For mosquito aquatic stages, there was a concentration-dependent decline in pupation and adult emergence rate (p < 0.0001). For the highest concentration of pyriproxyfen used for mosquito exposure, 7.8±0.1 ppb of pyriproxyfen was estimated in breeding water using the LC-MS/MS method. Results indicated that mosquitoes successfully auto-disseminated pyriproxyfen from the painted surfaces to the breeding habitats. Such formulations could be useful in intervention programmes after field-scale evaluation.