Empirical Support for the Pattern of Competitive Exclusion between Insect Parasitic Fungi

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.

Inductive Production of the Iron-Chelating 2-Pyridones Benefits the Producing Fungus To Compete for Diverse Niches

“… bassiana to outcompete M. robertsii in cocultures. This finding unveils a previously unsuspected tactic employed by B. bassiana to maintain coexistence in the environment since the fungus is inferior to compete with M. robertsii for insect individuals ( 31 ). It can be expected that the production of the iron-chelating 2-pyridones may also benefit the fungus to compete with other microbes.…”

“…Different insect-pathogenic fungi such as the Beauveria and Metarhizium species are omnipresent and coexistent in different environments and microniches ( 29 , 30 ). We have found that B. bassiana is inferior to compete for insect individuals with Metarhizium robertsii but could outcompete the latter when the two fungi were cocultured in artificial media ( 31 ). The mechanism(s) of this kind of antagonistic effect remains unclear.…”

Microbiome assembly on Drosophila body surfaces benefits the flies to combat fungal infections

“…It is common regarding the competitive antagonisms for nutrients and niches between microbes ( Douglas, 2019 ; Li et al., 2021 ). It is, therefore, not surprising to find that the dominant bacterial species isolated from the fly surfaces could all inhibit the germination of both the B. bassiana and M. robertsii spores.…”

Orchestrated Biosynthesis of the Secondary Metabolite Cocktails Enables the Producing Fungus to Combat Diverse Bacteria

“…Apart from the infection of insect hosts, M. robertsii has to outcompete other microbes for survival and dispersal in the field ( 16 , 20 ). We found that the deletion or the overexpression of UpmR did not apparently impair the ability of the fungus to battle the competitor fungus B. bassiana ( Fig.…”