Thiamethoxam induces transgenerational hormesis effects and alteration of genes expression in Aphis gossypii

Insecticide induced-hormesis, a bi-phasic phenomenon characterized by low dose stimulation and high dose inhibition following exposure to insecticide, is crucial to insect pest resurgence. In this study, the effects of low or sublethal concentrations of thiamethoxam on biological traits and genes expression were investigated for Aphis gossypii Glover following 72 h exposures. Leaf-Dip bioassay results showed that thiamethoxam was very toxic against adult A. gossypii with an LC50 of 1.175 mg L-1. The low lethal (LC15) and sublethal (LC5) concentrations of thiamethoxam significantly reduced longevity and fecundity of the directly exposed aphids. However, stimulatory effects on pre-adult stage, longevity, and fertility were observed in the progeny generation (F-1) of A. gossypii, when parental aphids (F-0) were exposed to LC15 of thiamethoxam. Subsequently, biological traits such as intrinsic rate of increase (r), finite rate of increase (lambda), and net reproductive rate (R-0) increased significantly to F-1 individuals due to LC15 treatment. No significant responses were observed for LC5 of thiamethoxam. The LC15 of thiamethoxam significantly increased the expression level of vitellogenin and ecdysone receptors genes in progeny generation, while no effects were observed for treatment with LC5. Additionally, the expression levels of P450 genes including CYP6CY14, CYP6CZ1, CYP6DC1, CYP6CY9, and CYP6DD1 were up-regulated in the exposed aphids. Taken together, our results show the hormetic effects of thiamethoxam on F-1 individuals, which might be due to the intermittent changes in expression of genes involved in fertility, growth and insecticide detoxification in A. gossypii.