Operational use of neem oil as an alternative anopheline larvicide. Part A: Laboratory and field efficacy.

We conducted a study to determine the laboratory and field efficacy of neem oil towards anopheline larvae. No difference in LC50 was observed between laboratory and field strains for temephos, chlorpyriphos-methyl/fenitrothion and neem oil. No difference in susceptibility was found after 3 months of application every 2 weeks. Water treated with a single application of traditional larvicides was free of larvae after 4 weeks; neem oil-treated water, however, was free after 2 weeks but not at 4 weeks. Application of chlorpyriphos-methyl/fenitrothion and neem oil every 2 weeks for 7 rounds resulted in dramatic reduction in larval density with no statistically significant differences. An adult survey after larviciding also showed no significant difference. The efficacy of crude neem oil appears to be below that of conventional larvicides.