Study of Pathogenesis Using Fluorescent Strain of Cordyceps farinosa Revealed Infection of Thitarodes armoricanus Larvae via Digestive Tract

Simple Summary Cordyceps farinosa is a widely distributed entomopathogenic fungus, which is highly infective and lethal to Thitarodes armoricanus larvae, thus it seriously endangers the Chinese cordyceps industry. Due to the lack of understanding of its infection process, there are currently no effective prevention and control strategies. In this study, we firstly obtained fluorescently labeled C. farinosa mutants by Agrobacterium-mediated transformation to better observe the pathway of C. farinosa infecting the T. armoricanus larvae. We then used the fluorescent C. farinose to infect T. armoricanus larvae. The results showed that the infection routes were through the body surface and the digestive tract. Our findings lay the foundation for further research and control of this pathogenic fungus. Cordyceps farinosa is often utilized as a biocontrol agent because of its wide host range, strong lethality, and safety for mammals. Artificial rearing of Thitarodes armoricanus larvae is a prerequisite for the artificial cultivation of Chinese cordyceps, and C. farinosa is the most lethal pathogenic fungus during the rearing process. However, the infection process of C. farinosa is still unclear. In this study, we cloned the promoter of the C. farinosa glyceraldehyde 3-phosphate dehydrogenase gene, constructed the EGFP expression cassette, and integrated it into the C. farinosa genome via Agrobacterium transformation. We obtained a fluorescent strain for better observation of the infection process. Using two different inoculation methods of the fluorescent strain, we observed the traditional infection process through the body surface as well as through the digestive tract via feeding. Both infection modes can lead to larval death and mummification. Our findings demonstrated that during the artificial rearing of T. armoricanus, preventing C. farinosa pollution should be an important part of the disinfection of the rearing environment.