Insecticidal properties of neem seed extracts: A review

The use of botanical pesticides such as azadirachtin found in the neem seed extract to control insect pests has increased globally due to its ability to maintain ecological safety. The objective of this review was to explore on different ways in which neem oil, the main extract from the neem seed, controls insect pests. Azadirachtin was found to be both a systemic and contact pesticide, hence repelling goeze on canola plants, while preventing settling and oviposition of the pea aphids. Antifeedant effect was achieved in lepidoptera family using an azadirachtin concentration of 1-50 and 100-600 ppm in cleoptera, homoptera and hemiptera families. Females of blanch showed less feeding than the males when treated with neem oil. The sugar receptors of desert locusts were blocked by an azadirachtin concentration of 0.01ppm and above, while the ability of the peach-potato aphid to transmit potato leafrol virus was reduced by the active substance. The fecundity, oviposition and the number of eggs laid by Drosophila melanogaster were reduced using a single spray of neem oil. Fecundity of aphid nymphs and the oviposition of cabbage aphids were reduced by azadirachtin. The pupation and eclosion of Drosophila melanogaster dropped significantly when the concentration of azadirachtin was increased. Early exposure of Drosophila melanogaster to azadirachtin slowed down the development of the adults by lowering the number of organisms, while delaying larval and pupal development. Resistance of pests to purified azadirachtin was found to be minimal, but zero to refined neem seed extracts. Neem seed extracts were reported to be biodegradable and non-toxic to humans, animals and natural enemies of pests. The efficacy of neem seed extracts in the control of insect pests, such as aphids, was found to be lower than that of the synthetic pesticides; hence a combination of neem oil with one or more other botanical pesticides is recommended in the attempt to increase the efficacy of botanical pesticides. Key words: Azadirachtin, fecundity, oviposition, sugar receptors