Larvicidal activity of methanolic plant extracts of Lantana cramera (P1) root and Anacardium occidentale (P2) leaf was investigated against the larvae of the three mosquito species (Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti reared in the laboratory), and the respective glutathione S-transferase (GST) activity was analyzed as an index of protection against the extracts. The LC₅₀ (extract concentration that shows 50% mortality) values of Pl extract for An. stephensi, Ae. aegypti, and Cx. quinquefasciatus were 132.55,27.82, and 11.68 ppm, respectively, whereas those of P2 extract were 56.81, 912, and 10.79 ppm, respectively. In general, in the untreated groups, the level of GST activity was significantly higher in Ae. aegypti in comparison with An. stephesi and Cx. quinquefasciatus. However, the enzyme activity failed to show any response when treated with either of the plant extracts in Ae. aegypti. However, an increase in the GST activity was recorded in extract-treated larvae of both An. stephensi and Cx. quinquefasciatus. The results of the current study suggest that both the plant extracts show species-specific mosquitocidal potential. Induction of GST activities in survived An. stephensi and Cx. quinquefasciatus larvae suggests the role of this enzyme in conferring resistance to the plant extracts.