Tuesday, December 14, 2010
Terrace Salon Two/Three (Town and Country Hotel and Convention Center)
The castor Ricinus communis (Euphorbiaceae), a plant that is distributed in warm and tropical areas, has emerged as an alternative against pests of agricultural, domestic and medical-veterinary the mosquitoes included. In this study evaluated the effect of hexane, ethyl acetate and methanol leaf extracts of castor on fourth instar larvae of the mosquito Culex quinquefasciatus (Diptera: Culicidae). The experimental unit consisted of a plastic cup containing 100 ml of distilled water and 20 early fourth instar larvae of C. quinquefasciatus, which received 1 ml of of each leaf extract with an emulsifier at concentrations ranging from 26 to 1250 ppm. This was replicated four times and compared with two blank treatments. When 95 % of the insects in the control with distilled water reached the pupae instar, the duration and viability of larvae and pupae were recorded, This information was used to quantify a Growth Inhibition Index (GII) and the mean lethal concentration (LC50). The larval and pupal viability data collection was continued with the surviving larvae and pupae, to determine the GII and viability at the end of the population´s life cycle. The IIC at 1250 and 625 ppm for hexane extract were 0.34 and 0.44, for the ethyl acetate extract were 0.34 and 0.46, and for the methanol extract were 0.25 and 0.53, respectively. Therefore, a moderate inhibition of the mosquito population growth was observed; the corresponding LC50´s were 416, 417 and 761 ppm. Data taken on surviving larvae at 1250 ppm showed a strong larvae growth inhibition and mortalities of 83.8, 88.8 and 100 % for the extracts with hexane, methanol, and ethyl acetate, respectively. Larval viability was affected by hexane and methanol extracts since 312.5 ppm, but the effects of the ethyl acetate extract started since 78 ppm. Thus, at these concentrations all the extracts decreased pupae viability and adult emergence, especially the hexane extract.