Larvicidal activity of Copaifera reticulata Ducke oil-resin against Culex quinquefasciatus Say (Diptera: Culicidae)
The appearance of resistance of Culex quinquefasciatus Say to chemical insecticides and the modification of the susceptibility of this mosquito to pyrethroid has stimulated studies on the activity of plants as alternative for its control. In this study, bioassays were carried out to verify the larvicidal activity of the oil-resin of Copaifera reticulata on C. quinquefasciatus. The bioassays were carried out with the oil dissolved in dimethylsulfoxide (DMSO), at the proportion of 0.4 ml of DMSO to 24.6 ml of distilled water. For each instar, the bioassays were carried out in plastic glasses with 100 ml solution using 20 larvae, wit four replications to adjust the lethal concentrations. The mortality observations were made after 48h exposure of the larvae to the solution. The control was carried out in distilled water and DMSO, with the same number of replications as the bioassays. The experiments were carried out in a biological chamber, controlled at 28 ± 1°C, 80 ± 5% relative humidity and 12h light. The larvae without movement were considered dead. The C. reticulata oil-resin demonstrated larvicide activity for all the C. quinquefasciatus instars. The LC50 found for the 1st, 2nd, 3rd and 4th larval instars were: 0.4, 0.9, 39 and 80 ppm, and the LC99 were 15, 15, 50 and 180 ppm, respectively.
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