Larvicidal activity and biochemical mode of action of Pinus halepensis essential oil from needles and brachyblasts against Culex pipiens mosquito larvae (Diptera: Culicidae)

The present study investigates the chemical composition and biological activities of Pinus halepensis essential oil (EO) extracted from needles and brachyblasts against the mosquito Culex pipiens. The EO was extracted by hydrodistillation and its chemical composition was analyzed using Gas Chromatography–Mass Spectrometry (GC–MS). Bioassays revealed a concentration-dependent larvicidal effect, with LC50 and LC90 values estimated at 17.78 μg/mL and 35.63 μg/mL, respectively. GC–MS analysis identified thirty-four (34) compounds, mainly belonging to sesquiterpenes (58.46%), monoterpenes (25.71%), and diterpenes (15.83%). The EO induced significant biological effects on the treated mosquito larvae at 24, 48, and 72 h after exposure to LC50 and LC90 concentrations. In addition, its impact on biochemical biomarkers, including acetylcholinesterase (AChE), glutathione S-transferase (GST), and sulfhydryl proteins (PSH), was evaluated. The results demonstrate that P. halepensis EO exerts significant neurotoxic effects through AChE inhibition. It also induced oxidative stress and activated detoxification pathways by increasing GST activity and decreasing PSH levels over time, with a highly significant treatment effect (p < 0.0001). To our knowledge, this is the first report describing both the larvicidal activity of P. halepensis EO and its ability to induce oxidative stress in Cx. pipiens larvae. These findings highlight the potential of this plant as a natural agent for sustainable and safe mosquito control. However, further studies on non-target organisms are required to assess its ecological safety.