The effects of extraction solvents on the toxicity of neem seed kernel extracts (NSKE) to Aedes aegypti 4th instar larvae was evaluated using the WHO standard procedures. The bioassay was conducted under varying laboratory conditions of temperatures of 35±5 0C and RH of 80±5%. The neem seed kernel extracted with hexane, benzene, ethyl acetate, acetone, DMSO, 2-propanol, ethanol and methanol were tested at concentrations of 0.25, 0.5, 1.0, 2.0 and 4.0 % (v/v) ml; while distilled water neem seed kernel extracts was evaluated at 5.0, 10.0, 15.0 and 20.0% (v/v) ml. Untreated distilled water served as control. Each treatment was replicated five times. Twenty, 4th instar larvae of Ae. aegypti were exposed to the various concentrations of NSKE extracted with different organic solvents and distilled water. The larvae were fed ad labitum with glucose and powdered animal liver mixed at a ratio of 2:3. Larval mortality was assessed after 1, 24 and 48 hours of exposure by inability to respond to probe and the LC50 values were computed. The results indicate that the most potent larvicides were hexane, 2-propanol, ethanol, acetone, methanol and DMSO extracted neem seed kernels which after one hour of exposure gave the lowest LC50 values of 0.71%, 1.26% and 2.21%, 2.27% and 3.39% (v/v) ml. respectively. The neem seed kernel extracted with benzene, ethyl acetate and distilled water have no larvicidal activity after one hour exposure. The paper discusses the possible use of neem seed kernel extracts in larvicidal mosquito control in the tropics.
Keywords: Solvents, Azadirachta indica, Seed Kernel Extracts, Aedes aegypti, Larvae, LC 50.