National Crops Resources Research Institute, P.O. Box 7084, Kampala, Uganda.
J Econ Entomol. 2010 Aug;103(4):1493-502. doi: 10.1603/ec09432.
"Sweetpotato weevils" Cylas puncticollis (Boheman) and Cylas brunneus F. (Coleoptera: Brentidae) are the most important biological threat to sweetpotato, Ipomoea batatas L. (Lam), productivity in sub-Saharan Africa. Sweetpotato weevil control is difficult due to their cryptic feeding behavior. Expression of Cylas-active Bacillus thuringiensis (Bt) Cry proteins in sweetpotato could provide an effective control strategy. Unfortunately, Bt Cry proteins with relatively high toxicity against Cylas spp. have not been identified, partly because no published methodology for screening Bt Cry proteins against Cylas spp. in artificial diet exists. Therefore, the initial aim of this study was to develop an artificial diet for conducting bioassays with Cylas spp. and then to determine Bt Cry protein efficacy against C. puncticollis and C. brunneus by using this artificial diet. Five diets varying in their composition were evaluated. The highest survival rates for sweetpotato weevil larvae were observed for diet E that contained the highest amount of sweetpotato powder and supported weevil development from first instar to adulthood, similar to sweetpotato storage roots. Seven coleopteran-active Bt Cry proteins were incorporated into diet E and toxicity data were generated against neonate C. puncticollis and second-instar C. brunneus. All Bt Cry proteins tested had toxicity greater than the untreated control. Cry7Aa1, ET33/34, and Cry3Ca1 had LC50 values below 1 microg/g diet against both species. This study demonstrates the feasibility of using an artificial diet bioassay for screening Bt Cry proteins against sweetpotato weevil larvae and identifies candidate Bt Cry proteins for use in transforming sweetpotato varieties potentially conferring field resistance against these pests.
“甘薯象甲” Cylas puncticollis（Boheman）和 Cylas brunneus F.（鞘翅目：象甲科）是撒哈拉以南非洲甘薯，Ipomoea batatas L.（Lam）生产的最重要的生物威胁。由于甘薯象甲的隐匿性取食行为，其防治较为困难。在甘薯中表达对 Cylas 有效的苏云金芽孢杆菌（Bt）Cry 蛋白可能提供一种有效的防治策略。不幸的是，尚未鉴定出对 Cylas spp.具有相对较高毒性的 Bt Cry 蛋白，部分原因是没有针对人工饲料中的 Cylas spp.筛选 Bt Cry 蛋白的已发表方法。因此，本研究的最初目的是开发一种人工饲料，用于进行 Cylas spp.的生物测定，然后使用该人工饲料确定 Bt Cry 蛋白对 C. puncticollis 和 C. brunneus 的功效。评估了五种不同组成的饲料。E 饲料中含有最高量的甘薯粉，支持象甲幼虫从第一龄期到成虫的发育，类似于甘薯贮藏根，观察到甘薯象甲幼虫的最高存活率。将七种鞘翅目活性的 Bt Cry 蛋白掺入 E 饲料中，并针对新生的 C. puncticollis 和第二龄期的 C. brunneus 生成毒性数据。测试的所有 Bt Cry 蛋白的毒性均大于未处理的对照。Cry7Aa1、ET33/34 和 Cry3Ca1 对两种物种的 LC50 值均低于 1μg/g 饲料。本研究证明了使用人工饲料生物测定筛选针对甘薯象甲幼虫的 Bt Cry 蛋白的可行性，并确定了用于转化可能赋予这些害虫田间抗性的甘薯品种的候选 Bt Cry 蛋白。
