Larvicidal and enzyme-inhibitory effects of essential oils from Eucalyptus globulus and Eucalyptus radiata against Culex pipiens

Abstract

Culex pipiens is among the most abundant mosquitoes in Algeria. This mosquito poses a significant public health risk as a vector of various diseases. Developing efficient and eco-friendly pesticides has also become a highly important issue to reduce the risks associated with conventional insecticides. In this context, the present study aimed to evaluate the responses of fourth-instar larvae of Culex pipiens (C. pipiens) to the effects of two essential oils (EOs) Eucalyptus globulus (E. globulus) and Eucalyptus radiata (E. radiata), both known for their bioinsecticidal properties. The oils were obtained by steam distillation and their chemical composition was determined using gas chromatography coupled to mass spectrometry (GC-MS). Larvicidal bioassays were conducted under laboratory conditions, and in silico analyses were performed to evaluate interactions between the major essential oils constituents and two detoxification enzymes acetylcholinesterase (AChE; PDB ID: 5X61) and glutathione S-transferase (GST; PDB ID: 18GS). E. radiata yielded a higher oil content (1.25 ± 0.36% w/w) than E. globulus (0.92 ± 0.48% w/w). GC-MS profiling revealed marked compositional differences: E. globulus EO was dominated by 1,8-cineole (72.05%), whereas E. radiata contained o-cymene (32.23%) as the main compound. Both EOs showed significant larvicidal activity (p<0.001) against C. pipiens, with E. globulus demonstrating greater potency (LC50 = 23.74 ppm) compared to E. radiata (LC50 = 53.42 ppm). In silico studies demonstrated that the major constituents of both essential oils exhibit strong insecticidal potential through various interactions with acetylcholinesterase and glutathione S-transferase. Compounds from Eucalyptus globulus showed slightly better binding affinities overall. These results support the development of safe and eco-friendly insecticides, offering a sustainable strategy for protecting both public health and the environment, especially through natural larvicides derived from essential oils targeting Culex pipiens mosquitoes.