Aquatic Larvicidal Efficacy of Periplaneta americana Chitin and Essential Oils Against Culex pipiens: A Comparative Assessment

With increasing resistance to chemical insecticides and mounting ecological concerns, the demand for eco-friendly mosquito control strategies has grown significantly. This study evaluated the physicochemical properties and larvicidal potential of chitin extracted from Periplaneta americana and compared its efficacy with several essential oils: orange, azadirachtin, jojoba, and an avocado–coconut oil blend against third-instar Culex pipiens larvae. FTIR and XRD analyses confirmed the extracted chitin as highly crystalline α-chitin, structurally comparable to commercial shrimp chitin. Elemental analysis and Degree of Acetylation (DA) values further verified high purity of extracted chitin. Despite its excellent structural integrity, chitin exhibited minimal larvicidal activity (LC₅₀ = 2428.54ppm; TI = 10.55) at 48 hours post-treatment. In contrast, orange oil showed the highest larvicidal efficacy (LC₅₀ = 256.30ppm; TI = 100), with larvae displaying pronounced neurotoxic symptoms, including uncoordinated movements and spasms. These observations prompted molecular docking analysis targeting the insecticide-resistant acetylcholinesterase (AChE) mutant of Anopheles gambiae (PDB ID: 6ARY). Key orange oil constituents, particularly sinensal and neryl acetate exhibited strong binding affinities and critical interactions with active-site residues, comparable to those of the co-crystallized inhibitor and chlorpyrifos. To validate these in-silico findings, biochemical assays were conducted and confirmed significant AChE inhibition, alongside notable reductions in larval carbohydrate, lipid, and protein levels. While chitin itself lacked direct larvicidal potency, its physicochemical stability, biocompatibility, and structural purity support its potential use as a delivery platform. We propose the development of chitin- or chitosan-based nano-formulations to encapsulate essential oils like orange oil, enhancing their stability, bioavailability, and sustained release for more effective and environmentally responsible mosquito control.