Larval control of <i>Culex vishnui</i> group through bio-active fraction of traveller's tree, <i>Ravenala madagascariensis Sonn</i>. (Strelitziaceae)

Abstract

Background and objectives: Due to ever increasing resistance against synthetic insecticides, mosquito control is fetching a serious problem all over the world. It is imperative to manage the vector population to conquer the mosquito born diseases. The present study was carried out to assess the target specific larvicidal activity of Ravenala madagascariensis against Culex vishnui group, the vector of Japanese Encephalitis. Methods: Crude extracts of R. madagascariensis matureleaves (foliages) ranging from 0.1% to 1.0% concentrations were tested against all the larval instars of Cx. vishnui group. Solvent extractions of matureleaves were carried out through three different solvents viz. petroleum ether, ethyl acetate and acetone from non-polar to polar trend. Larvicidal activities of the active fractions were examined against all the larval instars with graded concentrations ranging from 50 ppm to 250 ppm. LC 50 and LC 90 values were determined by log-probit analyses. Further statistical justifications were done through ANOVA analyses. Effectiveness of the bioactive fractions against non-target populations was executed in laboratory conditions. Phytochemical screening of leaf extract was also carried out. Result and Discussion: At 72 hours post-exposure, highest mortality (100%) with crude extract was found at 0.5% concentrations against all the instars. Amongst the three bioactive fractions, ethyl acetate extractives showed the highest larval mortality. After 72 hours of exposure, 200 ppm and 250 ppm concentration showed 100% mortality against 1 st and 2 nd instars larvae respectively. A 96.00% reduction in 3 rd instars mosquito population was recorded after 72 hours at 250 ppm concentration. However, 4 th instars larvae were subjected to only 84.00% reduction with these experimental set up and at 250 ppm concentration. The results of log probit analyses (95% confidence level) showed that LC 50 and LC 90 values were gradually decreased with the exposure periods having the lowest value at 72 h of exposure to 1 st instars larvae followed by 2 nd , 3 rd and 4 th instars larvae. Mortality rate (Y) was found to be positively correlated with the concentration (X) having a regression coefficient (R 2 ) close to 1 in each case. Phytochemical analyses revealed the qualitative presence of tannin, steroid and alkaloid free glycoside bound anthraquinones. Non target organisms were non-responsive to the bioactive fractions obtained from the plant throughout the experiment. Conclusion: From the above experiment it can be concluded that the mature leaves (foliages) of R. madagascariensis may be a superior larvicide alternative to the synthetic one.