Blastospores from and Are Not Always as Virulent as Conidia Are towards Caterpillars and Use Different Infection Mechanisms.

Infective conidia from entomopathogenic fungi are widely used to control insect pests. Many entomopathogenic fungi also produce yeast-like cells called blastospores under specific liquid culture conditions that can directly infect insects. However, little is known about the biological and genetic factors that allow blastospores to infect insects and make them potentially effective for biological control in the field. Here, we show that while the generalist produces a higher number of and smaller blastospores, the Lepidoptera specialist produces fewer propagules with a higher cell volume under high-osmolarity conditions. We compared the virulence of blastospores and conidia of these two species towards the economically important caterpillar pest . Conidia and blastospores from were equally infectious, but acted slower, and killed fewer insects than conidia and blastospores did, where conidia had the highest virulence. Using comparative transcriptomics during propagule penetration of insect cuticles, we show that blastospores express more virulence-related genes towards than do blastospores. In contrast, conidia of both fungi express more virulence-related oxidative stress factors than blastospores. Our results highlight that blastospores use a different virulence mechanism than conidia use, which may be explored in new biological control strategies.