Isolation and characterization of Bacillus thuringiensis strains active against Elasmopalpus lignosellus (Zeller, 1848) (Lepidoptera, Pyralidae)

ABSTRACT. Elasmopalpus lignosellus (Zeller, 1848) (Lepidoptera, Pyralidae) is an insect pest of 60 economically important crops, including sugarcane, wheat, soybean, rice, beans, sorghum, peanuts, and cotton. The aim of this work was to select and characterize Bacillus thuringiensis isolates with insecticidal activity against E. Lignosellus that could be used as an alternative method of control. Selective bioassays were done to evaluate the toxicity of 47 isolates against first instar larvae of E. lignosellus. For the most toxic bacterial strains, the lethal concentration (LC50) was estimated and morphological, biochemical and molecular methods were used to characterize the isolates. Among the 47 isolates tested, 12 caused mortality above 85% and showed LC50 values from 0.038E+8 to 0.855E+8 spores mL-1. Isolates BR83, BR145, BR09, BR78, S1534, and S1302 had the lowest LC50 values and did not differ from the standard HD-1 strain; the exception was BR83.The protein profiles produced bands with molecular masses of 60-130 kDa. The genes cry1, cry2, cry3, and cry11 were identified in the molecular characterization. The morphological analysis identified three different crystal inclusions: bipyramidal, spherical and cuboidal. Among the tested isolates, 12 isolates have potential for biotechnological control of E. Lignosellus by development of new biopesticides or genetically modified plants.

摘要。木质色埃螟（Elasmopalpus lignosellus）(Zeller, 1848)（鳞翅目（Lepidoptera）、螟蛾科（Pyralidae））是一种可危害60余种经济作物的重要害虫，寄主涵盖甘蔗、小麦、大豆、水稻、菜豆、高粱、花生及棉花等。本研究旨在筛选并鉴定对木质色埃螟具有杀虫活性的苏云金芽孢杆菌（Bacillus thuringiensis）菌株，为该害虫的防治提供替代方案。
本研究采用筛选性生物测定试验，评估了47株苏云金芽孢杆菌菌株对木质色埃螟1龄幼虫的毒力。针对毒力较强的菌株，测定了其致死中浓度（LC50），并通过形态学、生化及分子生物学方法完成菌株表征与鉴定。
在所测试的47株菌株中，有12株对幼虫的致死率超过85%，其LC50值范围为0.038×10^8至0.855×10^8孢子·毫升^-1。其中菌株BR83、BR145、BR09、BR78、S1534及S1302的LC50值最低，其杀虫活性与标准菌株HD-1无显著差异（菌株BR83除外）。
该类高毒力菌株的蛋白电泳图谱显示存在分子量介于60~130 kDa的蛋白条带；分子生物学鉴定结果表明，这些菌株携带cry1、cry2、cry3及cry11杀虫基因。形态学分析共观察到3种不同的晶体包涵体：双锥体形、球形及立方形。
综上，本研究筛选获得的12株苏云金芽孢杆菌菌株具备开发新型生物农药或转基因植物的潜力，可用于木质色埃螟的生物防治。