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.

摘要

烟草毛虫Spodoptera litura是一种主要害虫，影响多种作物（主要是蓖麻）的作物长势和产量。众所周知，昆虫病原体在害虫的生态友好管理中起着至关重要的作用。本研究旨在开发一种可自由流动的苏云金芽孢杆菌(Bt) WDG 制剂，该制剂含有高百分比的活性成分和可生物降解的佐剂。DOR Bt-127 的水分散颗粒 (WDG) 配方——苏云金芽孢杆菌变种的天然菌株。库尔斯塔基使用粘合剂（瓜尔胶）、润湿剂（Tween-80）和水溶性载体（淀粉）通过附聚和锅干燥法的组合制备。WDG 具有良好的润湿性，对S有效。斜文。X 射线衍射研究揭示了 WDG 制剂的半结晶性质。Bt WDG 制剂的 FTIR 光谱显示透射率峰值从 1636、1534 和 1075 cm ^-1的 Bt（技术）变化到 1631、1547 和 1147 cm ^-1，表明 Bt 与淀粉和瓜尔胶结合。该配方具有 134.7 mg/g 的高蛋白质含量和 74,200 SU/mg 对 9 天龄斜纹夜蛾的效力幼虫。盆栽研究和田间试验表明，Bt-127 WDG 制剂对 7 天和 9 天龄幼虫的效力与商业 Btk 制剂相当。Bt-127 WDG 制剂有望对抗早期和较老的龄期幼虫，因此有望用于生物密集型综合害虫管理计划，以减少合成化学杀虫剂的使用。