Toxicity, Histopathological Alterations and Acetylcholinesterase Inhibition of Illicium verum Essential Oil in Drosophila suzukii

In recent years, studies on the potential use of essential oils (EOs) as pesticides have enormously increased owing to their remarkable biological activities and health benefits. However, given the scant knowledge on the mode(s) of action behind insecticidal activity of individual essential oils, as well as their mixtures, much more work has yet to be undertaken. Furthermore, the variable and complex mixtures of essential oils suggest that their biological activities are likely due to several mechanisms acting on different physiological processes. Here, we firstly assessed the toxicity of Illicium verum, Myristica fragrans and Schinus molle EOs on Drosophila suzukii adults. Then, their acetylcholinesterase inhibitory activity as a potential mode of action was investigated. Subsequently, we explored potential structural alterations caused by exposure to low concentrations (LC20 and LC50) of I. verum oil on the fat body, midgut and muscular tissues of female flies. The results showed that the three EOs had good insecticidal activity against D. suzukii flies and although I. verum oil was more toxic than the two others, its acetylcholinesterase inhibition was the lowest. However, exposure to I. verum EO promoted severe concentration-dependent histological and structural alterations in the carbohydrate contents, muscle fiber, midgut epithelium as well as fat droplets area of exposed females. Collectively, our findings revealed that the insect’s internal organs are potential target sites of I. verum EO’s acute toxicity. Further studies are needed to confirm I. verum as a promising insecticidal compound against insect pests, to better elucidate its physiological and molecular action sites as well as assess its toxicity to non-target organisms.