Larvicidal activity of selected plant extracts and their combination against the mosquito vectors Culex quinquefasciatus and Aedes aegypti

In order to develop an environment-friendly botanical mosquito larvicide alternative to the chemical larvicides, extracts were made from the leaves of Hyptis suaveolens, Lantana camara, Nerium oleander, and Tecoma stans with three organic solvents such as methanol (ME), chloroform (CH), and petroleum ether (PE) using a Soxhlet extractor. The plant extracts were screened for larvicidal activity individually and in combination against the larvae of Aedes aegypti and Culex quinquefasciatus as per WHO protocol. Among the extracts, the maximum larvicidal activity was shown by the PE extract of L. camara (LC50 10.63 mg/L) followed by the PE extract of T. stans (LC50 19.26 mg/L), ME extract of N. oleander (LC50 35.82 mg/L), and PE extract of H. suaveolens (LC50 38.39 mg/L) against Cx. quinquefasciatus. In the case of Ae. aegypti, the PE extract of T. stans showed maximum activity with LC50 value of 55.41 mg/L followed by H. suaveolens (LC50 64.49 mg/L), PE extract of L. camara (LC50 74.93 mg/L), and ME extract of N. oleander (LC50 84.09). A blend of these four extracts resulted in a combination with corresponding LC50 values of 4.32 and 7.19 mg/L against Cx. quinquefasciatus and Ae. aegypti. The predator safety factors were 12.55 and 20.88 for Gambusia affinis with respect to Aedes and Culex larvae for the extract combination. Chemical constituents in extracts were also identified by FT-IR and GC-MS data. The present investigations suggest the possible use of this blend of botanical extracts as an ideal ecofriendly, larvicide against Ae. aegypti and Cx. quinquefasciatus larvae.