Impact of irrigation with fipronil-contaminated waters on zucchini plants and their main insect pest, Aphis gossypii

Abstract Fipronil is a long-lasting, broad-spectrum insecticide with low residual activity and high efficacy at low concentrations. Due to its widespread use and long half-life, fipronil can persist during wastewater treatment and is found even in surface waters. When released into the environment, it can accumulate over time and can lead to concentrations in soil and plant tissues that are harmful to both target and non-target organisms. Effective removal of fipronil is crucial in agricultural settings. Prolonged environmental exposure to this insecticide may contribute to the development of pesticide resistance and cross-resistance to other insecticides used for pest control in agro-ecosystems. As the reuse of treated wastewater and sewage sludge presents challenges and opportunities for farmers, this study investigates the effects of irrigation with environmentally relevant doses of fipronil on zucchini plants and their main insect pest, Aphis gossypii. The fitness costs of A. gossypii reared on plants irrigated with fipronil and their resistance to higher doses of fipronil and to pyrethrins were investigated in the laboratory. Traces of fipronil were found in the zucchini leaves, but not in the flowers, after 35-days of cumulative exposure. A decrease in nymph-to-adult survival and a dose-dependent reduction in the fecundity of A. gossypii feeding on contaminated host plants was observed. Also, aphids that ingested fipronil from the host plant exhibited the same mortality rate as the control group when exposed to a sub-lethal dose of fipronil. However, when natural pyrethrins were used, there was a significant increase in resistance to this insecticide. Our results demonstrate the potential for fipronil to accumulate in plant tissues and highlight the risk of changes in insecticide susceptibility in insect pests. This suggests a need for a holistic approach to the complex dynamics of wastewater reuse in agriculture.