Synergistic activity of Andrographis paniculata nees with Bacillus thuringiensis var israelensis against malarial vector, Anopheles stephensi Liston (Diptera: Culicidae)

Abstract

Integrated vector control is an effective and essential part of any successful vector control program. The synergistic activity between the current effective pesticides and phytochemicals is one such strategy and powerful tool for developing vector control strategies. Bacillus thuringiensis var israelensis (Bti) and ethanolic extracts (Ee) of Andrographis paniculata were both observed for their larvicidal as well as pupicidal activity against Anopheles stephensi Liston. Ee extract with lethal concentrations ($LC_{50}$ and $LC_{90}$) values of 36.56 and 53.04 p. p. m. after 24 h and $LC_{50}$ 22.28 and LC90 51.26 p. p. m. after 48h for fourth instar larvae, respectively. $LC_{50}$ and $LC_{90}$ for Bti were 0.0967 and 0.1003 p.p.m after 24h and 0.2944 and 0.4158 p. p. m. after 48 h of exposure for fourth instar larvae, respectively. Combined formulations were evaluated for synergistic activity and a 1:4 ratio of Bti and Ee was observed to be more effective than 1:2 and 1:1 ratios. However the larvicicdal activity is minimal when the mixed formulations contained an equal amount of both constituents (i. e a 1: 1 ratio). A ratio of 1: 4 of Bti and Ee of A. paniculata was 51.6 fold more toxic at the $LC_{90}$ for larvicidal activity, than Bti alone and this high level of activity resulted from synergism between the Bti and Ee of A. paniculata Nees.