Abstract

Objective: To evaluate the larvicidal activity of Ageratum houstonianum (A. houstonianum) crude leaf extracts against the immatures of vector mosquitoes. Methods: Bioassays were performed in the laboratory with hexane, ethyl acetate and methanol crude leaf extracts of A. houstonianum at concentrations of 62.5, 125, 250, 500, 1 000, 2 000, 4 000 and 8 000 mg/L against the third instar larvae of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus. Results: Poor larvicidal activity was observed. The lowest LC50 value was noted in ethyl acetate extract against all three vector mosquito species studied and was 3 377.84, 1 952.12 and 3 558.32 mg/L respectively after 24 h. The effect of toxicity was also manifested in a shorter period when compared to the other extracts viz., hexane and methanol. In Anopheles stephensi, more than 80% mortality was however observed at higher concentrations, after 24 h exposure in all the three extracts. In Aedes aegypti and Culex quinquefasciatus, this was observed by 3 and 24 h respectively in ethyl acetate extract. Conclusions: Screening of other parts of A. houstonianum with other solvents from different places for its larvicidal activity is recommended.

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