Effectiveness of neem extract and neem oil against Aedes aegypti (L.) and Culex quinquefasciatus Say larvae
2000
Manid Narksuwan
Investigation on the efficacy of neem extract (liquid form) which contained of azadirachtin 0.5 percent and neem oil obtained from seed kernel of Azadirachta indica tested against larvae of Aedes aegypti (L.) and Culex quinquefasciatus Say in the laboratory by dip bioassay method. The result showed that neem extract and neem oil were effective in controlling Aedes and Culex larvae. For insecticidal test, the neem extract at the concentration of 0.02 percent or more, one hundred percent mortality was obtained against fourth stage larvae of Ae. aegypti and Cx. quinquefasciatus while the neem oil at the concentration of 0.2 percent could completely control fourth stage larvae of Ae. aegypti and Cx. quinquefasciatus in 24 hours. Larvae that were exposed to need extract and neem oil at a lower concentration developed to pupal stage but failed to emerge, indicating that the neem extract and neem oil could inhibit development of pupae to adult. Study on the residual effect of neem extract and neem oil were found to be quite stable and remained effective for as long as 6 days in the laboratory. In semi-field trials, neem extract and neem oil applied at the concentration of 1, 2 and 4 times of LC100 could reduce the larval population and thereafter the efficacy declined.
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