Root-associated entomopathogenic fungi manipulate host plants to attract herbivorous insects

Abstract

Root-associated entomopathogenic fungi (R-AEF) indirectly infuence herbivorous insect performance. However, host plant-R-AEF interactions and R-AEF as biological control agents have been studied independently and without much attention to the potential synergy between these functional traits. In this study, we evaluated behavioral responses of cabbage root fies [Delia radicum L. (Diptera: Anthomyiidae)] to a host plant (white cabbage cabbage Brassica oleracea var. capitata f. alba cv. Castello L.) with and without the R-AEF Metarhizium brunneum (Petch). We performed experiments on leaf refectance, phytohormonal composition and host plant location behavior (behavioral processes that contribute to locating and selecting an adequate host plant in the environment). Compared to control host plants, R-AEF inoculation caused, on one hand, a decrease in refectance of host plant leaves in the near-infrared portion of the radiometric spectrum and, on the other, an increase in the production of jasmonic, (+)-7-iso-jasmonoyl-l-isoleucine and salicylic acid in certain parts of the host plant. Under both greenhouse and feld settings, landing and oviposition by cabbage root fy females were positively afected by R-AEF inoculation of host plants. The fungal-induced change in leaf refectance may have altered visual cues used by the cabbage root fies in their host plant selection. This is the frst study providing evidence for the hypothesis that R-AEF manipulate the suitability of their host plant to attract herbivorous insects.