Abstract: The aromatic nature of pine and cinnamon oils has established them as good adult repellents but their larvicidal efficacy against mosquitoes has not been explored much. Keeping this in view, laboratory studies were conducted to uncover the larvicidal potential of commercially available pine (Pinus longifolia) oil and cinnamon (Cinnamomum zeylanicum) oil against the early 4th instar larvae of Aedes aegypti, originating from Delhi, India. The larvicidal effects were investigated in terms of the larval mortality, behavioural and morphological changes, if any. Our studies revealed the larvicidal efficiency of both the oils against 4th instar larvae of Ae. aegypti, the pine oil proving to be more effective than the cinnamon oil. The LC₅₀ and LC₇₀ values exhibited by pine oil were 0.33093 mg/L and 0.54476 mg/L, respectively, while the values obtained with cinnamon oil were 0.63159 mg/L and 0.77736 mg/L, respectively. It was further observed that at LC₉₀ the larvicidal potential of cinnamon oil surpassed that of the pine oil, exhibiting a value of 1.11879 mg/L as in comparison to 1.04915 mg/L shown by pine oil. The behavioural changes as excitation, restlessness, tremors, and convulsions followed by paralysis observed in the treated larvae suggest a probable effect of the oils on their neuromuscular system. Microscopic study of morphological alterations in the treated larvae revealed that most of their organs had a normal structural appearance as that of controls except the little internal shrinkage in anal gills leading to the structural deformity. This indicates the anal gills as the probable action sites of the oil extracts and dysfunction of the gills leading to larval mortality. The potential of oils as new types of larvicides for the control of mosquitoes are explored.

Key words: Aedes aegypti, pine, cinnamon, larvicidal potential, anal gills, convulsions