Chronic effects induced by zinc oxide nanoparticles against larvae of the northern house mosquito Culex pipiens (Diptera: Culicidae)

Abstract

It is estimated that up to a million person are subject to death every year from mosquito-borne diseases. To avoid the epidemic situations arising from mosquito-borne diseases, it is necessary to reduce the mosquito populations. Challenges against efficient mosquito management are mainly related to emergence of insecticide resistance leading to increased need for the development of alternative methods. Ideal insecticides cause permanent impacts on the target insects in order to ensure powerful insecticidal effect. This study hypothesized that the impact of zinc oxide nanoparticles (ZnONPs) on the larvae of Culex pipiens Linnaeus, 1758 (Diptera: Culicidae) mosquito is irreversible and chronic. The first instar C. pipiens larvae were treated with a sublethal concentration (LC20, 0.24 g/L) of ZnONPs for 72 h and then allowed to recover for additional 72 h. Following the recovery period, the changes in zinc accumulation, growth rate, gut ultrastructure, biochemical changes in the hydrogen peroxide, antioxidant and detoxification enzymes were recorded and compared between recovered larvae and untreated (control). Recovered larvae showed significant increase in the accumulated zinc and reduced growth rate by about 50% compared to untreated (control). Furthermore, the ultrastructure of the alimentary canal epithelium showed several forms of pathological signs in different parts of the midgut of recovered larvae. Treatment with ZnONPs induced oxidative stress (OS) which appeared in the form of significant increase in hydrogen peroxide concentration. In response to OS, insects activate the detoxification system to get rid of the toxic nanoparticles. The detoxification enzyme alkaline phosphatase (ALP) and the antioxidant enzyme glutathione peroxidase (GPX) were inhibited while superoxide dismutase (SOD) was activated against ZnONPs toxicity. Additionally, recovered larvae didn’t show differences in the catalase activity from untreated control. These results verified that ZnONPs induce chronic impacts on C. pipiens larvae suggesting that it can be used in their management via direct application in standing water sources including accumulated rains and swimming pools.