Abstract
Background: Malaria is a leading public health problem in Ethiopia despite the implementation of effective indoor vector control strategies over several decades. Vector control operations in the country largely depend on the application of Indoor Residual Spraying (IRS) of synthetic insecticides and Long Lasting Insecticidal Nets (LLINs) which resulted in a significant reduction in the malaria burden. The spread of resistance to insecticides in these indoor vector control tools in vector species is a serious challenge. Alternatively, reports indicate that botanicals which are relatively safe possess toxic compounds with high larvicidal activities. However, there are limited evidences on the larvicidal effect of botanicals against the malaria vectors, Anopheles arabiensis . This study aimed to evaluate the larvicidal activities of the extracts of the roots, stems, and leaves of Parthenium hysterophorus against the 4 th instar larvae of An. arabiensis . Methods: Field collected leaves, stems and root parts of P. hysterophorus were dried and separately ground to powder and extracted in petroleum ether, hexane, acetone, and ethanol solvents. The extracts were concentrated using a Rota evaporator, and stock solutions were subject to serial dilutions for use as test concentrations. Laboratory reared 4 th instar larvae of An. arabiensis were used for the larvicidal bioassays. Mortality data were subjected probit analysis to determine LC 50 and LC 90 of the extracts. Results: The results showed that there were significant differences in percentage larval mortalities (P<0.05) among different concentrations of the leaf, stem, and root solvent extracts, respectively. Hexane extracts of leaves and stem of P. hysterophorus at 480ppm caused the highest mortality of 4 th larval instar of An. arabiensis (85% and 96.7%, respectively) compared to those of ethanolic, acetone, and petroleum ether extracts of these plant parts. Petroleum ether extracts of the root of P. hysterophorus were the most effective in causing very high larval mortality at 360ppm and 480ppm (98.3%). The LC 50 value of petroleum ether root extract (10.7ppm) and LC 90 value of petroleum ether root extract (105.5ppm) were significantly lower than those of ethanol, acetone, and hexane root extracts, respectively. Conclusion: Petroleum ether root extract of P. hysterophorus has remarkably high larvicidal potential against 4 th instar larvae of An. arabiensis which could be exploited for malaria vector control. Further studies on the larvicidal efficacy of the extracts under field conditions and identification of the bioactive components in the root parts of this weed plant are recommended.
Evaluation of larvicidal activities of Parthenium hysterophorus L. against Anopheles arabiensis (Diptera: Culicidae), the major malaria vector in Ethiopia