Neonicotinoids are modern insecticides widely used in agriculture worldwide. Their impact on target (nervous system) and non-target (midgut) tissues has been well studied in bene cial insects including honeybees. However, their effects on pest insects on the eld are comparably rarely described. Here, we have studied the effects of the neonicotinoid imidacloprid on the midgut of the pest insect Locusta migratoria caught in the eld. We found that in the midgut of imidacloprid-exposed locusts the activity of enzymes involved in reactive oxygen metabolism was perturbed. By contrast, the activity of P450 enzymes that have been shown to be activated in a detoxi cation response and that were also reported to produce reactive oxygen species was elevated. Probably as a consequence, markers of oxidative stress including protein carbonylation and lipid peroxidation accumulated in midgut samples of these locusts. Histological analyses revealed that their midgut epithelium is disorganized and that the brush border of the epithelial cells is markedly reduced. Indeed, microvilli are signi cantly shorter, misshapen and possibly non-functional in imidacloprid-treated locusts. We hypothesize that imidacloprid induces oxidative stress in the locust midgut, thereby changing the shape of midgut epithelial cells and probably in turn compromising their physiological function. Presumably, these effects reduce the survival rate of imidacloprid-treated locusts and the damage they cause in the eld.
BackgroundBecause of its devastating impact on agriculture, the locust Locusta migratoria migratorioides is considered the most economic important pest in Assuit governorate in Upper Egypt. The existing control methods against these pest rely on chemical insecticides such as imidacloprid, chlorpyriphos, malathion and others (El-Saad et al. 2017), which are harmful to the environment and potentially also to humans.Since their introduction in the nineties of the last century, neonicotinoids have become the most widelyused chemical class of insecticide in many countries (Casida &Durkin 2013, Jeschke &Nauen 2008, Jeschke et al. 2011, Tomizawa &Casida 2005. Due to their speci city to insects concomitant with low acute toxicity to non-insects and their versatility in application methods, neonicotinoids constitute an attractive tool in modern agriculture (Elbert et al. 2008, Thompson et al. 2020). However, concerns over neonicotinoids are emerging, and in the European Union, for instance, the use of several neonicotinoids has been widely restricted because of their adverse effects on honeybees (https://ec.europa.eu/food/plants/pesticides/approval-active-substances/renewalapproval/neonicotinoids_en) (Thompson et al. 2020, Wood &Goulson 2017. Hence, for the next future, it is important to assess the impact of neonicotinoids and to understand their effects on the insect at the molecular and cellular levels.Neonicotinoids target primarily at the nervous systems of insects as agonists of postsynaptic acetylcholine receptors by binding especially to the α su...