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.
Highlights
By coinfection of insects with different species and strains of M. robertsii and B. bassiana each with a wide host range, we report the dominant mycosis of insect individuals by one species or one strain of the parasites
Previous coinfection of insects resulted in the dominant mycosis of insects by single species of parasitic fungi [18,37,38]
Our empirical data suggest that the competitive exclusion principle (CEP) would fit for the pattern and outcome of fungal parasite competitions for insect individuals
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Fungi are the second most species-rich eukaryotic group after the insects [1,2]. After long-term coevolution, different relationships have been formed between insects and fungi such as the pattern of the insect infection and mycosis by parasitic fungi. Similar to the distribution features of diverse insect species, fungal parasites are largely cosmopolitan and sympatrically distributed in different ecosystems [3]. It has been reported that the propagules of the ascomycete Metarhizium and Beauveria species could reach up to
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