Development of a water dispersible granule (WDG) formulation of<i>Bacillus thuringiensis</i>for the management of<i>Spodoptera litura</i>(Fab.)

Abstract

The tobacco caterpillar, Spodoptera litura is a key insect pest affecting the crop stand and yield of a wide range of crops, mainly castor. Entomopathogens are known to play a vital role in eco-friendly management of insect pests. The present study was undertaken with the objective of developing a freely flowable WDG formulation of Bacillus thuringiensis (Bt) containing a high percentage of active ingredient coupled with biodegradable adjuvants. Water dispersible granule (WDG) formulation of DOR Bt-127 – a native strain of B. thuringiensis var. kurstaki was prepared by a combination of agglomeration and pan drying method using a binder (guar gum), a wetting agent (Tween-80) and a water-soluble carrier (starch). WDG had good wettability and was effective against S. litura. X-ray diffraction studies revealed semi-crystalline nature of WDG formulation. FTIR spectra of Bt WDG formulation revealed change in transmittance peaks to 1631, 1547 and 1147 cm−1 from 1636, 1534 and 1075 cm−1 of Bt (technical) indicating binding of Bt with starch and guar gum. The formulation has a high protein content of 134.7 mg/g and potency of 74,200 SU/mg against 9 days old S. litura larvae. Pot culture studies and field trials revealed that efficacy of Bt-127 WDG formulation was on par with the commercial Btk formulation against 7 and 9 days old larvae. Bt-127 WDG formulation was promising against early as well as older instar larvae and therefore has a prospective to be used in Bio-intensive Integrated Pest Management programmes to reduce the usage of synthetic chemical insecticides.