Larvicidal Activity of Melissa officinalis and Rosmarinus officinalis Extracts and Their Lethal Impact on Detoxifying Enzymes in Aedes aegypti L. Larvae

Background & Objectives: Mosquito-borne diseases significantly impact global health, particularly in tropical regions. While synthetic insecticides are currently employed to control mosquito vectors, their detrimental effects on ecosystems and persistence necessitate alternative control methods. Botanicals, owing to their diverse phytocompounds, offer potential for controlling and preventing vector-borne diseases by targeting insect eggs and larvae. This study aimed to evaluate the toxicity of Melissa officinalis and Rosmarinus officinalis extracts (methanolic and aqueous) against Aedes aegypti larvae, a vector of arboviruses. Materials & Methods: Total protein content in control and plant extract-exposed larval homogenates was estimated using bovine serum albumin as a standard. Acetylcholinesterase (AChE) and carboxylesterase assays were performed to determine larvicidal effects. Larval mortality was assessed after 24 hours of exposure. Results: Our findings revealed that the methanolic leaf extract of M. officinalis exhibited superior larvicidal activity (100% at 1000 ppm) compared to the methanolic R. officinalis extract (84±2.45% at 1000 ppm). In contrast, the aqueous extracts of both plant species inferred no larvicidal activity. The LC50 and LC90 values for M. officinalis methanolic extract were 378.7 ppm and 795.8 ppm, respectively, whereas those for R. officinalis were 648.9 ppm and 1152.9 ppm, respectively. Furthermore, biochemical assays measuring total protein, acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase activities were conducted for M. officinalis, corroborating and substantiating its larvicidal properties. Conclusion: This study demonstrates that the methanolic leaf extract of M. officinalis possesses significant larvicidal efficacy against A. aegypti. These findings suggest that this plant or its phytocompounds could serve as a bioinsecticide, offering a potential alternative to environmentally toxic and non-biodegradable synthetic insecticides.