OVICIDAL ACTIVITY OF NEEM PRODUCTS (AZADIRACHTIN) AGAINST CULEX TARSALIS AND CULEX-QUINQUEFASCIATUS (DIPTERA, CULICIDAE)

Bioactive compounds contained in the seed kernel and other parts of th e neem tree (Azadirachta indica A. Juss) have been found to show insec ticidal activities and other effects in many species of insects. These activities include antifeedancy, growth regulation, fecundity suppres sion, male sterility, oviposition repellency, changes in biological fi tness such as loss of flying ability, immunodepression, enzyme inhibit ion, splitting of biological rhythms, and so forth. We investigated th e ovicidal effects of various formulations of azadrirachtin (AZ) again st the mosquitoes Culex tarsalis Coquillett and Culex quinquefasciatus Say. The formulations tested were wettable powder Azad(TM) WP10, emul sifiable concentrate Azad(TM) EC4.5, and technically pure AZ. The ovic idal activity of the test neem products was influenced by concentratio n of AZ, age of the egg rafts, and age of the neem preparations. Other factors such as formulation and mosquito species were also involved i n the degree of ovicidal activity. When the egg rafts were deposited d irectly in fresh neem suspension and left there for 4 h before transfe r to untreated water, 1 ppm of AZ produced almost 100% mortality in eg gs. When egg rafts aged for 0, 4, 8, 12, and 24 h were exposed to 10 p pm neem suspensions for 36 h, the ovicidal activity was only attained in the egg rafts deposited directly (0 h old) in the neem suspension, not in those with ages of 4-24 h. On aging, depending on the formulati ons and mosquito species, the neem suspensions at 1 ppm completely los t ovicidal activity within 7-20 days. The egg rafts of Cx. quinquefasc iatus were more susceptible to the test neem products than those of Cx . tarsalis. The formulated neem products were more persistent and effe ctive than the technical AZ. The wettable powder (WP) formulation was slightly more persistent and effective than the emulsifiable concentra te (EC). The ovicidal activity of the neem products against mosquitoes from the current research clearly demonstrated the potential of neem products as possible ovicides against Culex mosquitoes.