Female mosquitoes display preferences for certain individuals over others, which is determined by differences in volatile chemicals produced by the human body and detected by mosquitoes. Body odour can be controlled genetically but the existence of a genetic basis for differential attraction to insects has never been formally demonstrated. This study investigated heritability of attractiveness to mosquitoes by evaluating the response of Aedes aegypti (=Stegomyia aegypti) mosquitoes to odours from the hands of identical and non-identical twins in a dual-choice assay. Volatiles from individuals in an identical twin pair showed a high correlation in attractiveness to mosquitoes, while non-identical twin pairs showed a significantly lower correlation. Overall, there was a strong narrow-sense heritability of 0.62 (SE 0.124) for relative attraction and 0.67 (0.354) for flight activity based on the average of ten measurements. The results demonstrate an underlying genetic component detectable by mosquitoes through olfaction. Understanding the genetic basis for attractiveness could create a more informed approach to repellent development.

The reproductive capacity of S. exigua is significantly reduced in Delta-SEL and Gos-SEL populations compared with the control group (SS-Strain). Elevation of the major detoxification enzyme cytochrome P450 monooxygenase and esterase might have an important role in inducing tolerance to deltamethrin in gossypol-fed S. exigua populations. This study enhances our understanding of detoxification enzyme pathways for S. exigua gene expression and their role in responses to insecticides and plant secondary metabolites. © 2018 Society of Chemical Industry.

Plants employ an intricate and dynamic defense system that includes physiological, biochemical, and molecular mechanisms to counteract the effects of herbivorous attacks. In addition to their tolerance to phytotoxins, beet armyworm has quickly developed resistance to deltamethrin; a widely used pyrethroid insecticide in cotton fields. The lethal concentration (LC50) required to kill 50% of the population of deltamethrin to gossypol-fed Spodoptera exigua larvae was 2.34-fold higher than the control group, suggesting a reduced sensitivity as a consequence of the gossypol diet. Piperonyl butoxide (PBO) treatment was found to synergize with deltamethrin in gossypol-fed S. exigua larvae. To counteract these defensive plant secondary metabolites, beet armyworm elevates their production of detoxification enzymes, including cytochrome P450 monooxygenases (P450s). Gossypol-fed beet armyworm larvae showed higher 7-ethoxycoumarin-O-deethylase (ECOD) activities and exhibited enhanced tolerance to deltamethrin after 48 and 72 h when compared to the control. Moreover, gossypol pretreated S. exigua larvae showed faster weight gain than the control group after transferring to a deltamethrin-supplemented diet. Meanwhile, gossypol-induced P450s exhibited high divergence in the expression level of two P450 genes: CYP6AB14 and CYP9A98 in the midgut and fat bodies contributed to beet armyworm tolerance to deltamethrin. Knocking down of CYP6AB14 and CYP9A98, via double-stranded RNAs (dsRNA) in a controlled diet, rendered the larvae more sensitive to the insecticide. These data demonstrate that generalist insects can exploit secondary metabolites from host plants to enhance their defense systems against other toxic chemicals. Impairing this defense pathway by RNA interference (RNAi) holds a potential to eliminate the pest’s tolerance to insecticides and, therefore, reduce the required dosages of agrochemicals in pest control.