Larvicidal effects of bio-insecticide against filariasis vector, Culex quinquefasciatus

Cx. quinquefasciatus is a vector for lymphatic filariasis and West Nile fever, diseases for which no vaccine is available. Hence, controlling the population of this mosquito requires urgent attention. Synthetic insecticides are widely used for this purpose. However, the limitations associated with their usage, including the triggering of resistance development and non-target toxicities, necessitate the exploration of alternative, eco-friendly solutions. This study investigated the larvicidal effects of eight medicinal plants against Cx. quinquefasciatus. Notably, with the exception of Ocimum basilicum and Tagetes erecta, the insecticidal activity of the remaining six plants has not been previously studied, to our knowledge. Larvicidal efficacy was assessed following the WHO bioassay protocols. The larvicidal bioassay results showed that stigmasterol isolated from the ethyl acetate fraction of O. basilicum leaves was highly effective as a larvicidal agent (LC50 value of 34.97 ppm, i.e., < 50 ppm)). To our knowledge, stigmasterol was isolated from O. basilicum for the first time in this study. Among the tested extracts of the eight selected plants, the ethyl acetate fraction of O. basilicum exhibited the next highest potency (LC50 value of 97.72 ppm) with moderate larvicidal effectiveness ((LC50 values > 50 ppm and < 100 ppm), whereas the chloroform fraction (LC50 value of 115.32 ppm) and n-hexane fraction of Pistacia integerrima (LC50 value of 298.02 ppm) were effective (LC50 values > 100 ppm and < 300 ppm). In contrast, the crude methanolic extracts and their soluble fractions (n-hexane, chloroform, and ethyl acetate) from the remaining six plants, as well as the crude methanol extract and n-hexane fraction of O. basilicum and the crude methanol extract and chloroform and ethyl acetate fractions of P. integerrima, exhibited less effectiveness as larvicidal agents (LC50 values > 300 ppm). These findings highlight stigmasterol as a highly effective natural larvicidal agent, offering a promising natural and sustainable alternative for integrated mosquito management.