Bodyguard Interactions: A Beneficial Endophyte Triggers Emission of Methyl Salicylate in Infested Tomato Plant Mediating Attraction of a Parasitoid Wasp.

The endoparasitoid Dolichogenidea gelechiidivoris is a potential candidate biocontrol agent of Phthorimaea absoluta. We previously reported that the endophyte Trichoderma asperellum M2RT4 triggers the systemic release of key phytohormones in tomato affecting the behavior and herbivory of P. absoluta. As D. gelechiidivoris uses odor cues to locate P. absoluta, we therefore investigated the chemical basis of interactions between D. gelechiidivoris, the tomato plant with and without endophyte and P. absoluta through bioassay-guided chemical analysis. Y-tube olfactometer bioassays showed that the parasitoid was significantly attracted to P. absoluta-infested tomato plants but did not show preference to colonized and colonized-infested plants. Coupled GC–MS analyses revealed both qualitative and quantitative differences in volatile emission between non-colonized, colonized, non-colonized infested and colonized-infested plants, where volatile emission rate increased with increasing infestation level. Methyl salicylate (MeSA) emission was significantly higher in colonized-infested than in colonized and non-colonized infested plants. Subsequent bioassays revealed attraction of the parasitoid to synthetic MeSA emitted at its natural release rate from endophytically-colonized infested plants. Our findings highlight the significant role played by MeSA, which mediates the attraction of D. gelechiidivoris thereby indirectly assisting tomato plants in combatting P. absoluta.