Variation of major limonoids in Azadirachta indica fruits at different ripening stages and toxicity against Aedes aegypti.

The azadirachtin, salannin, nimbin, deacetylnimbin, azadiradione and epoxyazadiradione contents were determined by HPLC in the fractions prepared from the kernel of neem fruits (Azadirachta indica) collected at different ripening stages. The fully mature fruit (yellow fruits) kernels contained the highest concentration of azadirachtin, nimbin and salannin, whereas the concentration of azadiradione (NC) and epoxyazadiradione (NL) was high in the unripe green berries. The toxicity of the fractions (KEA-1 to KEA-5) obtained from the kernels collected at successive intervals, as well as of the pure limonoids referred to above was evaluated against 3rd instar larvae of Aedes aegypti L. (wild strain). It was observed that the toxicity of these fractions increased with the maturity of the fruits. An interesting observation was that the toxicities of KEA-3 to KEA-5 are comparable and the concentration of all the major limonoids is optimum in KEA-3, which suggested that these exert a joint effect against Aedes aegypti.