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Abstract：
Fungal entomopathogens are largely facultative parasites and play an important role in controlling the density of insect populations in nature. A few species of these fungi have been used for biocontrol of insect pests. The pattern of the entomopathogen competition for insect individuals is still elusive. Here, we report the empirical competition for hosts or niches between the inter- and intra-species of the entomopathogens Metarhizium robertsii and Beauveria bassiana. It was found that the synergistic effect of coinfection on virulence increase was not evident, and the insects were largely killed and mycosed by M. robertsii independent of its initial co-inoculation dosage and infection order. For example, >90% dead insects were mycosed by M. robertsii even after immersion in a spore suspension with a mixture ratio of 9:1 for B. bassiana versus M. robertsii. The results thus support the pattern of competitive exclusion between insect pathogenic fungi that occurred from outside to inside the insect hosts. Even being inferior to compete for insects, B. bassiana could outcompete M. robertsii during co-culturing in liquid medium. It was also found that the one-sided mycosis of insects occurred during coinfection with different genotypic strains of either fungi. However, parasexual recombination was evident to take place between the compatible strains after coinfection. The data of this study can help explain the phenomena of the exclusive mycosis of insect individuals, but co-occurrence of entomopathogens in the fields, and suggest that the synergistic effect is questionable regarding the mixed use of fungal parasites for insect pest control.
摘要：
真菌昆虫病原体主要是兼性寄生虫，在控制自然界昆虫种群密度中起重要作用。这些真菌的一些物种已用于害虫的生物防治。昆虫病原体竞争昆虫个体的模式仍然难以捉摸。这里,我们报告了昆虫病原菌绿僵菌和球孢白僵菌的种间和种间对宿主或壁ni的经验竞争。发现共感染对毒力增加的协同作用不明显，并且这些昆虫大部分被M.robertsii杀死和真菌感染，而与最初的共同接种剂量和感染顺序无关。例如,即使在将巴氏杆菌与M.robertsii浸入9：1的混合比例为9：1的孢子悬浮液中，仍有>90％的死昆虫被M.robertsii真菌化。因此，结果支持了从昆虫宿主外部到内部发生的昆虫病原真菌之间的竞争性排斥模式。甚至不如竞争昆虫，在液体培养基中共培养过程中，球孢芽孢杆菌的竞争能力超过了M.robertsii。还发现，昆虫的单侧真菌病发生在与两种真菌的不同基因型菌株共感染期间。然而,混合感染后，相容菌株之间明显发生了无性重组。这项研究的数据可以帮助解释昆虫个体的专有真菌病现象，但是昆虫病原体在田野中同时出现，并建议将真菌寄生虫混合用于害虫防治，其协同作用值得怀疑。
