Antifeedancy of neem products containing Azadirachtin against Culex tarsalis and Culex quinquefasciatus (Diptera: Culicidae).

In order to develop and utilize new botanical insecticides originating from neem (Azadirachta indica A. Juss) in mosquito control programs as a potential larvicide, the antifeedant activity of three formulations of neem against the larvae of Culex tarsalis Coquillett and Culex quinquefasciatus Say was investigated under laboratory conditions. A significant antifeedancy was indicated at 5 ppm and 10 ppm azadirachtin (AZ) for all formulations and both species. Within the test concentration range of AZ (1-10 ppm), 5 ppm was the minimum effective concentration for antifeedancy in most cases. Some differences in larval susceptibility in terms of antifeedancy to the test formulations were noted between the two species. The Cx. tarsalis larvae were more susceptible than Cx. quinquefasciatus larvae to Azad EC 4.5 at 1 ppm during the first 15-min exposure period and at 5 and 10 ppm during the whole test period. The Cx. quinquefasciatus larvae were more susceptible than Cx. tarsalis larvae to Azatin WP 4.5 at 1, 5, and 10 ppm during the first 15-min exposure period or to Neemix EC 4.5 at 1 ppm during the first 45-min exposure period. The formulation-related differences in antifeedant activity appeared when the concentration increased from 1 to 10 ppm. In Cx. tarsalis, the Azad EC 4.5 and Neemix EC 4.5 were more effective than Azatin WP 4.5 at 5 ppm during the first 15-min exposure period and at 10 ppm during the whole test period. In Cx. quinquefasciatus, the Azatin WP 4.5 and Neemix EC 4.5 were more effective than Azad EC 4.5 at 1 ppm during the first 30-min exposure period, and at 5 ppm during the first 60-min exposure period, and at 10 ppm during the whole test period.