Age-dependent Aedes mosquito resistance profiling and mortality rate to repeated insecticides exposure in Western region, Saudi Arabia

BackgroundLittle is documented on Aedes aegypti age-dependent role on different resistance mechanisms to repeated insecticides exposures. The study examined the age-dependence of mortality rate and genetic resistance in two mechanistically pyrethroid resistant mosquito strains exposed once or repeatedly at different ages. MethodsWHO bioassays and real time polymerase chain reaction (qPCR) were performed to ascertain their association between age-dependent exposures related mortality rate and single/repeated resistance in the Jeddah and Makkah. Candidate genes of interest (CYP9J7, CYP9J27, CYP9J26, AAEL006953, CYP9P450, AAEL006013) were assessment. ResultsAge dependent and exposure duration had a significant effect on the survival of the Jeddah and resistant Cayman. Our results showed that in a single exposure assays, age had no significant effect on mortality in the Cayman strain ({chi}2=2.76, df=1, P=0.097), but there was significantly increased mortality in the Jeddah strain younger age ({chi}2=5.46, df=1, P=0.02), but not statistically significant at older age. In the multiple exposure assay, GLiM analysis showed a significant strain, day and strain*day interaction indicating mortality rate is influenced by the strain or day (which also corresponds to age).The Jeddah strain showed generally lower survival,, there was a highly significant association of survival with repeated exposures in the Jeddah strain ({chi}2=43.6, df=1, P=4.1x10E-11) and the Cayman strain ({chi}2=12.5, df=1, P=0.0004). Mortality rate correlated statistically and significantly with the number of days of exposure in the Cayman strain (Spearman rank correlation {rho}=-0.77, P=0.01), but in the Jeddah strain it was not statistically significant ({rho}= -0.42, P=0.23). After repeated insecticide exposure, the AAEL006013 was statistically and significantly over-expressed compared to the control (P=0.03). ConclusionTo the best of our knowledge, this is one of the first research on age and exposure linked genomic and bioassay on field Ae. aegypti in Jeddah, KSA. The study showed that repeated exposure to pyrethroids reduced the Aedes mosquito population mortality rate. This suggests that there is indeed increasing age-dependent resistance or survival with multiple exposure high-doses of same or repeated insecticide, thus indicating the need to rethink on integrated vector control policy and interventions and technical assistance in the Kingdom.