Sublethal concentrations of imidacloprid increase reproduction, alter expression of detoxification genes, and prime Myzus persicae for subsequent stress

Hormesis, a biphasic phenomenon characterized by low-dose stimulation and high-dose inhibition following exposure to stress, has been reported in many different insects exposed to low doses of pesticide. Using green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), and the insecticide imidacloprid as a model, we tested whether or not there were changes in expression of genes involved in insecticide detoxification and general stress when aphids were exposed over multiple generations in a greenhouse setting to imidacloprid concentrations that induced hormetic responses. We also wanted to know whether exposure to insecticide concentrations that induce reproductive hormesis impacted the insect’s ability to cope with a subsequent stressor. The instantaneous rate of increase and total reproductive output of aphids developing on potato plants treated with 0.25 µg imidacloprid L⁻¹ was significantly greater than that on control plants. Treatments of 0.25 and 2.5 µg imidacloprid L⁻¹ significantly increased or decreased expression of genes for E4-esterase, cytochrome P450-CYP6CY3, and Hsp60 in aphids, with variation within and across generations. Third-generation aphids from plants treated with 0.25 µg imidacloprid L⁻¹ survived longer than control aphids when subsequently subjected to food/water stress, but not when subsequently exposed to a LC20 of another insecticide. Our results indicate insecticide-induced reproduction hormesis in M. persicae is accompanied by intermittent changes in expression of detoxification and stress-coping genes, and that it can prime the insect to cope with subsequent stress.