Characterization and evaluation of Bacillus thuringiensis var. kurstaki based formulation for field persistence and insect biocontrol

Commercial formulations of Bacillus thuringiensis do not deliver in the field trials, mainly due to short persistence and residual efficacy of bioagent. In the present investigation, different subspecies of Bacillus thuringiensis were evaluated for their larvicidal potential and using the most promising subspecies, B. thuringiensis kurstaki, Wettable powder (WP) formulation addressing these issues was developed by us. The laboratory developed formulation was evaluated for efficacy under laboratory and field conditions. WP formulation was observed to meet all the criteria set for physico-chemical parameters according to the FAO/WHO specifications. Spore counts and toxicity obtained in this formulation were considerably higher than those obtained in the commercial formulation of B. thuringiensis kurstaki. The developed formulation considerably improved the persistence of B. thuringiensis kurstaki under field conditions. Under field trial on cabbage (Brassica oleracea var. capitata), this formulation significantly reduced number of leaves damaged; and improved marketable yield of cabbage heads. It could effectively control pests in the field for 10 days after spray. It was very effective in the control of Pieris brassicae, Spilarctia obliqua, Plutella xylostella and Spodoptera litura. Thus, WP formulation of B. thuringiensis kurstaki, developed by us, has good potential for effective biocontrol of insect pests in the field, due to its longer persistence and delivery of higher dose of active ingredient on the crop.