Larvicidal activity of methanolic and aqueous extracts of Lavandula dentata and Nerium oleander flowers against the vector of avian malaria Culiseta longiareolata

In light of the adverse effects of chemical insecticides on the environment and human health, as well as the development of mosquito resistance to them, this study explores the potential of methanol and aqueous flower extracts from Lavandula dentata and Nerium oleander as bioinsecticides against Culiseta longiareolata mosquitoes. Additionally, it aims to assess the impact of these extracts on enzymatic biomarkers and biochemical composition of fourth instar larvae of Culiseta longiareolata.Qualitative analysis revealed the presence of flavonoids, terpenes, gallic and catechic tannins in both plant extracts. Sterols and quinones were exclusively found in L. dentata, while saponins were identified in N. oleander. methanolic extracts demonstrated higher yields compared to aqueous extracts. The results showed significant larvicidal activity for all the tested extracts, the LC₅₀ values after 24 hours are: 463.8; 338.1; 760.9 and 99.64 ppm for the aqueous and methanolic extract of L. dentata and N. oleander respectively. This proves that the methanolic extracts of N. oleander and L. dentata have higher efficacy against C. longiareolata compared to the aqueous extracts. Enzymatic activity assays conducted on larvae treated with various extracts, particularly at LC₂₅ and LC₅₀ concentrations, indicated an induction of the detoxification system, evidenced by increased glutathione S-transferases (GSTs) and catalase activity. Morphometric analysis revealed a significant reduction in the growth of fourth-stage larvae treated with these extracts. As well as a notable decrease of a percentage ranging from 44.23 to 83.30% in protein content; a reduction between 38.15-78.57% in carbohydrates and a percentage decrease of 23.85 to 63.58% in lipids. These findings suggest that the observed effects may be attributed to the stressful conditions imposed by the treatment, necessitating additional energy supply from carbohydrate and lipid metabolism in the larvae.