Zhang Lei, Shi Wei-Bing, Feng Ming-Guang
School of Biological and Chemical Engineering, Zhejiang University of Science & Technology, Hangzhou 310023, PR China; Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou 310058, PR China.
Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou 310058, PR China.
J Invertebr Pathol. 2014 Mar;117:73-8. doi: 10.1016/j.jip.2014.02.005. Epub 2014 Feb 22.
Entomopathogenic fungi can infect and kill spider mite eggs but their ovicidal activities are poorly understood. Here we gain histopathogenical and molecular insights into the ovicidal activities of Beauveria bassiana and Isaria fumosorosea against the two-spotted spider mite, Tetranychus urticae. Scanning electronic microscopy indicated successful adhesion and germination of fungal conidia on egg shell at 24h post-spray (HPS). Germ tubes of both fungi could penetrate into egg shell with penetration pegs at 48 HPS. Interestingly, the germ tubes of B. bassiana may elongate on egg surface to locate appropriate sites for penetration, acting as 'searching' hyphae. Aside from the normal penetration, the germ tubes of I. fumosorosea can be completely or partially embedded into egg shell for a distance of extension, forming shell humps. Light microscopy of ultrathin sections of infected eggs showed shrunken (affected) or disrupted embryos at 48-96 HPS despite little effect on egg cleavage at 24 HPS. However, distinguishable hyphal cells were hardly found inside the embryos lacking oxygen although fungal outgrowths were abundant on unhatched (killed) eggs. In PCR with specific probes, the 18S rDNA signals of B. bassiana (412 bp) and I. fumosorosea (454 bp) in the DNA extracts from surface-cleaned mite eggs increased at 0-96 HPS, confirming fungal colonization in the infected eggs. We consider that the colonization on shell surface and underside could rely upon extending hyphae for uptake of egg nutrition, resulting in embryo disruption. Our observations add knowledge to microbial control of spider mites.
昆虫病原真菌能够感染并杀死叶螨卵，但其杀卵活性却鲜为人知。在此，我们对球孢白僵菌和玫烟色棒束孢对二斑叶螨（Tetranychus urticae）的杀卵活性进行了组织病理学和分子层面的深入研究。扫描电子显微镜显示，喷雾后24小时（HPS），真菌分生孢子成功附着并在卵壳上萌发。两种真菌的芽管在48 HPS时均可通过侵入栓穿透卵壳。有趣的是，球孢白僵菌的芽管可能会在卵表面伸长，以找到合适的穿透位点，起到“搜索”菌丝的作用。除了正常穿透外，玫烟色棒束孢的芽管可以完全或部分嵌入卵壳一段延伸距离，形成卵壳隆起。对感染卵超薄切片的光学显微镜观察显示，在48 - 96 HPS时胚胎出现萎缩（受影响）或破裂，尽管在24 HPS时对卵裂影响不大。然而，在缺氧的胚胎内部几乎找不到可区分的菌丝细胞，尽管在未孵化（已死亡）的卵上真菌生长旺盛。在使用特异性探针的PCR中，从表面清洁的螨卵DNA提取物中，球孢白僵菌（412 bp）和玫烟色棒束孢（454 bp）的18S rDNA信号在0 - 96 HPS时增加，证实真菌在感染的卵中定殖。我们认为，在卵壳表面和底部的定殖可能依赖于延伸的菌丝来摄取卵的营养，从而导致胚胎破裂。我们的观察为叶螨的微生物防治增添了知识。
