李嘉++王小奇
摘 要 香蕉象甲(Cosmopolites sordidus)是芭蕉属(Musa spp.)经济作物最具破坏力的害虫,如何对其进行有效防治已成为一项重要议题。球孢白僵菌(Beauveria bassiana)在香蕉象甲防治方面具有很好的应用效果,对其应用研究的主要成果进行概述,这对以后进一步研究球孢白僵菌等昆虫病原真菌及其在害虫防治上的应用具有重要的参考价值。
关键词 球孢白僵菌 ;香蕉象甲 ;防治 ;内生菌
分类号 S436.67
An Overview of Application Study of Beauveria bassiana
in the Control of Cosmopolites sordidus
LI Jia WANG Xiaoqi
(Plant Protection College, Shenyang Agricultural University, Shenyang, Liaoning 110866)
Abstract The banana weevil Cosmopolites sordidus is the most devastating insect pest of banana crops (Musa spp.), so how to control it effectively has been an important issue. The fungus Beauveria bassiana exhibits good application effects in the control of C. sordidus, and the major achievements are shown in this paper. This will provide a reference for further study on B. bassiana and other entomopathogenic fungi, and their application in pest control.
Keywords Beauveria bassiana ; Cosmopolites sordidus ; control ; endophyte
香蕉象甲(Cosmopolites sordidus Germar)隶属于鞘翅目(Coleoptera)象甲科(Curculionidae),是世界上多数芭蕉属(Musa spp.)经济作物生产区最具破坏力的害虫[1],该属几乎所有种类都能深受其害,若不加以控制,损失可以达到100%[2]。这种害虫在假茎和根茎中钻蛀、取食,导致植株养分摄取减少、成熟延迟、叶片早衰、茎秆断折等[3-6];同时,受害植株对其它害虫和疾病变得更加易感[7]。受害严重的植株或许在其果实串形成之前已经死亡,因而使果实产量下降[4,6]。因此,如何有效防治这种害虫已成为一项重要议题。
农业防治方法如利用寄主作物的假茎和根茎诱捕香蕉象甲成虫,抗性作物品种的培育和利用,作物残留物的及时清除等均已用于香蕉象甲的治理,但成本和劳动投入较高[5,8]。化学杀虫剂已在商业种植园大量使用,但香蕉象甲很快表现出了抗性,并且其它弊端例如环境污染和高成本进一步限制了其使用[9-10]。香蕉象甲的捕食性天敌虽有记录,例如1种甲虫腹点纹牙甲(Dactylosternum abdominale)和1种蚁Odontomachus troglodytes,但它们在香蕉象甲防治上的应用效果常常不够理想[11-13]。目前,昆虫病原真菌在香蕉象甲防治方面具有很好的应用效果,且主要是一种称为球孢白僵菌[Beauveria bassiana (Balsamo) Vuillemin]的丝状真菌,其隶属于丝孢纲、丛梗孢目、丛梗孢科、白僵菌属。这种真菌对许多昆虫都具有明显的致病性,因此是研究及应用最多的真菌类生物杀虫剂[14-17]。
1 研究进展
球孢白僵菌是香蕉象甲生物防治最具使用价值的制剂之一[18]。在许多室内测试中,球孢白僵菌表现出对香蕉象甲的高致病性;在一些田间试验中,这种真菌的使用同样能够显著抑制香蕉象甲的种群数量[7,19-20]。
球孢白僵菌的毒力在不同的菌株间存在差别[16,21]。对香蕉象甲具有高毒力的1个菌株(CG1024)有1种分子标记,对该菌株具有专一性,它是通过随机扩增多态性DNA(Random Amplified Polymorphic DNA, RAPD)图谱比对而发现的[16]。这种分子标记经克隆和测序之后,设计出它的专一性PCR引物,用于扩增其一段838 bp的片段。这可用于这个菌株的田间探查和监测,并判断其防治香蕉象甲的效力[16]。
球孢白僵菌同一菌株的不同剂型在防治香蕉象甲的效力上也存在差异[19]。有人研究了1种球孢白僵菌菌株的2种剂型对香蕉象甲的防治效力[19]。这2种剂型分别是纯孢子粉剂和以磨碎的脱脂油棕榈仁为基质的孢子粉剂。它们虽然能使人工散放的香蕉象甲种群产生同等高水平的死亡率,但对香蕉象甲的自然种群,带基质的剂型导致的死亡率要显著高于纯孢子粉剂。这种差别可能源于这2种剂型的孢子存活力的不同[19]。
受球孢白僵菌侵染的香蕉象甲在田间的活动范围信息对于如何有效散布这种病原菌具有重要意义[19]。受侵染的寄主会在田间活动时散播病原菌,并将其传染给其它香蕉象甲,形成流行的态势[19,22-23]。这样既实现了对害虫种群的抑制,同时又减少了病原菌的初始用量和再次施用的必要性[19]。使用病原菌人工侵染的香蕉象甲成虫,有人研究了球孢白僵菌在田间的传播情况,结果表明该菌的孢子可能会从香蕉象甲起始释放点散播达18 m的距离[19]。endprint
香蕉象甲的群集信息素能够增强球孢白僵菌的传播,从而提高防治香蕉象甲的效果[23]。这里群集信息素用于将香蕉象甲吸引到球孢白僵菌的施用地点,而后球孢白僵菌借助受侵染的香蕉象甲的活动进行传播[23]。研究表明,比起单独使用球孢白僵菌,联合使用球孢白僵菌与香蕉象甲信息素能明显导致更高水平的香蕉象甲死亡率[23]。有了群集信息素的协助,球孢白僵菌的单位面积施用量可以得到减少[23]。另外,植物利它素也能够有效吸引并群集香蕉象甲,它们在协助病原菌传播而防治香蕉象甲方面的作用也值得进一步研究。植物利它素的使用优势就是它们具有易得性[23]。
2 存在问题及局限性
作为香蕉象甲的微生物杀虫剂,球孢白僵菌的使用也会受到一些因素的制约,如不良环境条件(温度、光照、降水等)、生产制剂的高成本、不完善的应用技术等[24-28]。另外,香蕉象甲的生物学特性也增加了根除它的难度,因为在具有严重危害性的幼虫期,它生活在香蕉根茎的内部,从而受到了很好的保护[3]。为了应对这些限制因素,将球孢白僵菌作为人工内生菌来使用是可取的方法。内生菌的使用优势就是它能消灭香蕉根茎内部的香蕉象甲幼虫,同时由于只需要少量的菌剂,应用成本也降低了[7,28]。内生的球孢白僵菌也可以在香蕉植株的内部受到保护,从而避开田间限制它使用的非生物和生物因素[7,28]。
近年来的研究表明,球孢白僵菌能够在许多植物种类,包括组织培养得到的香蕉植株中以内生菌形式存活[7,29-32]。对组织培养的香蕉植株进行球孢白僵菌悬浮液接种,建立内生菌群的比例可达78.7%,并且持续了至少4个月[33-34];后来又有证据表明,这种成功建立内生菌群的比例可高达96.7%[35]。这些香蕉植株内的人工菌群不会对植株生长造成不利影响,即使在接种时使用了很高剂量的球孢白僵菌[34-35]。
香蕉植株的内生球孢白僵菌对香蕉象甲的作用效果已有研究。在乌干达,有人对组织培养的香蕉植株进行球孢白僵菌接种,方法即将植株的根浸在球孢白僵菌悬浮液(孢子浓度1.5×107个/mL)中,持续2 h[7,28]。植株生长2个月后引入香蕉象甲成虫或幼虫。当引入成虫5 d后,香蕉植株的内生球孢白僵菌没有对成虫产卵率以及卵孵化率造成影响;但经过15周后,这些内生球孢白僵菌大大减少了香蕉象甲种群数量以及它们对香蕉植株的危害[7]。当引入幼虫2周后,内生球孢白僵菌显著降低了幼虫存活率以及它们对香蕉植株的危害[28]。对于同一植株,内生菌群建立程度越高的部位受香蕉象甲的危害越小[7,28]。据称内生球孢白僵菌对香蕉象甲的作用方式可以是直接寄生,或者是在香蕉植株组织中积累真菌毒素,这些毒素能够遏制香蕉象甲的取食和发育,从而减少其对香蕉植株的危害[7]。以后的研究需要改善内生球孢白僵菌群建立的程度和持久性,以更有效地减少香蕉象甲的危害。内生球孢白僵菌对香蕉象甲的田间防治效果试验是必不可少的,这与它的实际应用相关联。
3 应用前景与展望
球孢白僵菌在香蕉象甲防治方面具有良好的应用前景,相信在昆虫病原生物学、化学生态学、分子生物学等研究的推动下,其应用效果将会不断提升。将球孢白僵菌和香蕉象甲的引诱剂(信息素或它感物质)联合使用以促进球孢白僵菌的散播,以及通过香蕉植株的内生球孢白僵菌控制隐藏于植株内部的香蕉象甲幼虫都是很有前途的应用方法。病原真菌类除了球孢白僵菌,绿僵菌属的Metarhizium anisopliae对香蕉象甲也具有致死作用[36-37],因此如何将球孢白僵菌与绿僵菌有效联合施用以增强对香蕉象甲的防控能力有必要深入探讨。研究表明球孢白僵菌和绿僵菌的本地菌株对香蕉象甲的毒力较弱,因此外来菌株的使用或许是理想的选择[38]。另外,一些昆虫病原线虫如Steinernema carpocapsae、Heterorhabditis bacteriophora等也能够有效侵染并杀死香蕉象甲,从而应用于香蕉象甲的防治[13,39]。综合应用球孢白僵菌和其它病原真菌、病原线虫等要素以提高香蕉象甲的防治效果有待于进一步研究,这也需要有害生物综合治理(Integrated Pest Management, IPM)的理论指导。本文对以后进一步研究球孢白僵菌等昆虫病原真菌及其在害虫防治上的应用具有重要的参考价值。
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