Sublethal exposure of emamectin benzoate and thiamethoxam alters the biological parameters and genes expression in Aedes aegypti (Diptera: Culicidae)

Abstract

Excessive use of agrochemicals results in contamination of water due to runoff or leaching. Insecticide induced-hormesis, a phenomenon characterized by low dose stimulation following exposure to insecticide, is crucial to insect pest resurgence. In this study, the effects of low or sublethal concentrations of emamectin benzoate and thiamethoxam on biological traits and genes expression were investigated for yellow fever mosquito, Aedes aegypti following 48 h exposures. Bioassay was conducted to compute LC₁₀ and LC₂₀ values for both test insecticides. The low lethal (LC₁₀) and sublethal (LC₂₀) concentrations of emamectin benzoate and thiamethoxam significantly reduced longevity and fecundity of the exposed mosquitoes. However, population parameters showed a negative change in the F₁ progeny of emamectin exposed A. aegypti mosquitoes. While, stimulatory effects on pre-adult stage, longevity, and fertility were observed in the progeny generation (F₁) of A. aegypti, when parental generation (F₀) were exposed to LC₁₀ and LC₂₀ of thiamethoxam. However, at F₂ generation the population parameters in all the treatments were statistically similar to the control except in the LC₂₀ treatment of emamectin benzoate. The LC₁₀ and LC₂₀ of thiamethoxam significantly increased the expression level of vitellogenin in progeny generation, while inhibitory effects were observed for both treatments of emamectin benzoate. Additionally, the expression levels of P450 genes including CYP6P15, CYP6BB2, and CYP9J26 were up-regulated in the exposed insects. Taken together, our results show the hormetic effects in thiamethoxam on F₁ and F₂ individuals, which might be due to the intermittent changes in expression of genes involved in fertility, growth and insecticide detoxification in A. aegypti.