Okumu Fredros O, Knols Bart G J, Fillinger Ulrike
University of Nairobi, School of Biological Sciences, Nairobi, Kenya.
Malar J. 2007 May 22;6:63. doi: 10.1186/1475-2875-6-63.
Larviciding is a key strategy used in many vector control programmes around the world. Costs could be reduced if larvicides could be manufactured locally. The potential of natural products as larvicides against the main African malaria vector, Anopheles gambiae s.s was evaluated.
To assess the larvicidal efficacy of a neem (Azadirachta indica) oil formulation (azadirachtin content of 0.03% w/v) on An. gambiae s.s., larvae were exposed as third and fourth instars to a normal diet supplemented with the neem oil formulations in different concentrations. A control group of larvae was exposed to a corn oil formulation in similar concentrations.
Neem oil had an LC50 value of 11 ppm after 8 days, which was nearly five times more toxic than the corn oil formulation. Adult emergence was inhibited by 50% at a concentration of 6 ppm. Significant reductions on growth indices and pupation, besides prolonged larval periods, were observed at neem oil concentrations above 8 ppm. The corn oil formulation, in contrast, produced no growth disruption within the tested range of concentrations.
Neem oil has good larvicidal properties for An. gambiae s.s. and suppresses successful adult emergence at very low concentrations. Considering the wide distribution and availability of this tree and its products along the East African coast, this may prove a readily available and cheap alternative to conventional larvicides.
杀幼虫剂是全球许多病媒控制项目中使用的关键策略。如果能在当地生产杀幼虫剂，成本可能会降低。对天然产物作为针对非洲主要疟疾媒介冈比亚按蚊的杀幼虫剂的潜力进行了评估。
为评估印楝（印楝属）油制剂（印楝素含量为0.03%w/v）对冈比亚按蚊的杀幼虫效果，将三龄和四龄幼虫暴露于添加不同浓度印楝油制剂的正常饲料中。一组幼虫对照组暴露于类似浓度的玉米油制剂中。
8天后，印楝油的LC50值为11ppm，其毒性几乎是玉米油制剂的五倍。在浓度为6ppm时，成虫羽化受到50%的抑制。在印楝油浓度高于8ppm时，除了幼虫期延长外，还观察到生长指数和化蛹率显著降低。相比之下，玉米油制剂在测试的浓度范围内未产生生长干扰。
印楝油对冈比亚按蚊具有良好的杀幼虫特性，并能在极低浓度下抑制成虫成功羽化。考虑到这种树及其产品在东非海岸广泛分布且易于获取，这可能成为传统杀幼虫剂的一种现成且廉价的替代品。
