Abstract
Entomopathogenic fungi such as Beauveria bassiana are currently considered as a potential control agent for malaria mosquitoes. The success of such strategies depends among others on the efficacy of the fungus to kill its hosts. As B. bassiana can use various resources for growth and reproduction, increasing the dependency on mosquitoes as a nutritional source may be instrumental for reaching this goal. Passage of entomopathogenic fungi through an insect host has been shown to increase its virulence. We evaluated the virulence, fungal outgrowth, mycelial growth rate, and sporulation rate of two B. bassiana isolates (Bb1520 and Bb8028) that underwent 10 consecutive selection cycles through malaria mosquitoes (Anopheles coluzzii) using an experimental evolution approach. This cycling resulted in an altered capacity of evolved B. Bassiana lineages to grow on different substrates while maintaining the ability to kill insects. Notably, however, there were no significant changes in virulence or speed of outgrowth when comparing the evolved lineages against their unevolved ancestors. These results suggest that fungal growth and sporulation evolved through successive and exclusive use of an insect host as a nutritional resource. We discuss the results in light of biocontrol and provide suggestions to increase fungal virulence.
Highlights
Beauveria bassiana is a cosmopolitan ascomycete fungus which is able to live as a saprophyte in the soil, as an endophyte in plants, and as an entomopathogen affecting a broad range of arthropods (Rehner et al, 2011)
Increased efficacy of entomopathogenic fungi is an important prerequisite for their successful deployment as a biological control agent of insects
We first assessed whether our selection scheme could result in the fixation of phenotypic changes and, secondly, whether we could select for higher fungal virulence using this approach
Summary
Beauveria bassiana is a cosmopolitan ascomycete fungus which is able to live as a saprophyte in the soil, as an endophyte in plants, and as an entomopathogen affecting a broad range of arthropods (Rehner et al, 2011). Exploiting technical and biological (non-GMO) resources is a feasible and a realistic alternative to increase the efficacy of fungal biological control agents In this regard, various efforts have been made to improve the delivery of spores to the insect, including UV protectants and humidity stabilizers, and using different growth substrates that increase sporulation, virulence, and stress resistance (Jaronski, 2010). We evaluated (i) whether B. bassiana is suitable for experimental evolution by assaying the potential to evolutionary changes of growth parameters and (ii) whether it is possible to select for higher fungal virulence against mosquitoes. We test our evolved lineages for changes in fungal virulence against mosquitoes and discuss our results in light of biocontrol strategies
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