Larvicidal, Biological and Genotoxic Effects, and Temperature-Toxicity Relationship of Some Leaf Extracts of Nerium oleander (Apocynaceae) on Culex pipiens (Diptera: Culicidae)

BACKGROUND: The present study was undertaken to study the larvicidal activity of different extracts of Nerium oleander leaves, and post-treatment temperature- toxicity relationship of these extracts against Culex pipiens. Further, the most potent extract was used to evaluate its biological and genotoxic activities. METHODS: Crude extracts of N. oleander leaves were prepared using water, chloroform, acetone and diethyl ether as solvents. Extraction was carried out using soxhlet apparatus. Bioassay test was carried out on the larvae, and the LC(50) of each extract was determined. Thus, newly hatched first instar larvae were treated, and the mortality count was recorded daily till pupation (accumulated mortality). The LC(50) of diethyl ether extract, as the most potent extract, was used for the further biological and genotoxic studies. RESULTS: The results obtained indicated that diethyl ether extract of N. oleander leaves was the most potent extract, with LC(50) of 10500 mg/l. The toxicity of the four extracts, using the LC(50), at 10 °C was higher than that at 35 °C. The LC(50) of diethyl ether extract significantly decreased the larval duration, pupal duration, percentage of pupation, percentage of adult emergence, longevity of females, fecundity, and oviposition activity index, whereas the growth index and the percentage of development per day of larvae and pupae were significantly increased compared to non-treated insects. Moreover, treatment with this extract induced significant dominant lethality in both male and female adults. CONCLUSION: It appears that diethyl ether extract of N. oleander leaves is potential control agent to Cx. pipiens.