Department of Agricultural Biology, Jeonbuk National University, Jeonju, South Korea.
Department of Forest Resources, AgriBio Institute of Climate Change Management, College of Agriculture & Life Sciences, Chonnam National University, Gwangju, South Korea.
Pest Manag Sci. 2022 Aug;78(8):3356-3364. doi: 10.1002/ps.6962. Epub 2022 May 20.
Beauveria bassiana is one of the commercially available entomopathogenic fungi (EPF), and a number of isolates with high virulence and broad host spectrum have been used to control agricultural and forest pests. Although the functional importance of genes in EPFs' pathogenesis have been extensively studied, the precise ultrastructural mechanism of the fungal infection, particularly penetration of the host insect cuticles, is not well understood.
In this study, we investigated the morphology and ultrastructure of the larval cuticle of the red flour beetle, Tribolium castaneum, after treatment with B. bassiana ERL1170 expressing an enhanced green fluorescent protein (Bb-eGFP). The Bb-eGFP showed high virulence against the larvae, with approximately 90% mortality at 48 h after treatment (HAT) and 100% at 72 HAT under our infection conditions. In these larvae, the regions of the body wall with flexible cuticles, such as the ventral and ventrolateral thorax and abdomen, became darkly melanized, but there was little to no melanization in the rigid dorsal cuticular structures. Confocal microscopy and transmission electron microscopy (TEM) indicated that germinated conidia on the surface of the larval cuticle were evident at 6 HAT, which formed penetration pegs and began to penetrate the several cuticle layers/laminae by 12 HAT. The penetration pegs then developed invading hyphae, some of which passed through the cuticle and reached the epidermal cells by 24 HAT. The larval cuticle was aggressively and extensively disrupted by 48 HAT, and a number of outgrowing hyphae were observed at 72 HAT.
Our results indicate that Bb-eGFP is capable of infection and penetrating T. castaneum larvae shortly after inoculation (~24 HAT) at the body regions with apparently flexible and membranous cuticles, such as the ventral intersegmental regions and the ventrolateral pleura. This study provides details on the histopathogenesis of the host cuticle by infection and penetration of EPFs, which can facilitate the management of insect pests. © 2022 Society of Chemical Industry.
球孢白僵菌是一种商业上可利用的昆虫病原真菌（EPF），许多具有高毒力和广泛宿主谱的分离株已被用于防治农业和森林害虫。尽管 EPF 发病机制中的基因的功能重要性已得到广泛研究，但真菌感染的精确超微结构机制，特别是穿透宿主昆虫表皮，尚不清楚。
在这项研究中，我们研究了球孢白僵菌 ERL1170 表达增强型绿色荧光蛋白（Bb-eGFP）处理后赤拟谷盗幼虫表皮的形态和超微结构。Bb-eGFP 对幼虫表现出高毒力，在我们的感染条件下，处理后 48 小时（HAT）时约有 90%的幼虫死亡，72 HAT 时 100%死亡。在这些幼虫中，体壁具有柔软表皮的区域，如腹面和腹侧面的胸部和腹部，变得深黑色，而刚性的背侧表皮结构几乎没有黑化。共聚焦显微镜和透射电子显微镜（TEM）表明，处理后 6 HAT 时，表面的萌发分生孢子明显，形成穿透钉并开始穿透数层表皮/薄片，在 12 HAT 时开始穿透。穿透钉然后发育出侵入性菌丝，其中一些在 24 HAT 时穿过表皮到达表皮细胞。在 48 HAT 时，幼虫表皮被强烈且广泛地破坏，在 72 HAT 时观察到许多向外生长的菌丝。
我们的结果表明，Bb-eGFP 能够在接种后不久（约 24 HAT）感染并穿透 T. castaneum 幼虫，特别是在表皮柔软且具有膜状的部位，如腹节间区和腹侧侧板。本研究提供了 EPF 感染和穿透宿主表皮的组织病理学发病机制的详细信息，有助于害虫的管理。© 2022 化学工业协会。
