Fitness consequences of oviposition choice by an herbivorous insect on a host plant colonized by an endophytic entomopathogenic fungus

Several species of entomopathogenic fungi (EPF), often considered as bioinsecticides, are able to colonize and establish a symbiotic relationship with plants as endophytes. Recent studies have demonstrated that insects feeding on endophytically colonized plants could have reduced survival. These newly emerging, but not yet fully understood, ecological roles suggest the possibility that EPF may affect preferences and performance of herbivorous insects. However, such plant-mediated effects and underlying mechanisms are largely unexplored. Here, we examined that the endophytic EPF, Beauveria bassiana, could affect oviposition selection and offspring fitness of Asian corn borer, Ostrinia furnacalis on maize, Zea mays. We observed that O. furnacalis females preferred to lay eggs on B. bassiana-inoculated maize plants. This was attributed to the changes in plant volatile profiles upon endophytic colonization by B. bassiana. Of these plant volatiles, we observed increased amounts of insect-preferred compounds, 2-ethyl-1-hexanol and 3-hexen-1-ol, and decreased amounts of non-preferred compounds β-caryophyllene, naphthalene and α-pinene. This finding suggests that B. bassiana-induced plant volatiles could modulate the interactions between plants and insects. However, fewer O. furnacalis larvae, pupae, and adults survived on the B. bassiana-colonized maize plants and this was correlated with lower plant nitrogen content in these plants. These results indicated that oviposition selection of O. furnacalis did not reflect the maximization of offspring fitness following maize inoculation with B. bassiana. We suggest that EPF-inoculated maize causes a detrimental attraction for O. furnacalis, which should be considered for potential application of “trap plants” when incorporating endophytic EPF within integrated pest management programs.