Red-rot infection in sugarcane attenuates the attractiveness of sugarcane borer-induced plant volatiles to parasitoid

Abstract

Fungal phytopathogens are known to induce changes in plant metabolite profile and defense levels that consequently affect insect herbivores. Although it is expected that fungal plant infection may also affect herbivore natural enemies that are guided by plant chemical cues, few studies have addressed this interaction. Here, we examined the effect of infection in sugarcane by the red-rot fungus, which is usually associated with the injury of the sugarcane-borer Diatraea saccharalis, on plant defenses by assessing borer weight gain and the attractiveness of herbivore-induced plant volatiles to the parasitoid Cotesia flavipes. Olfactometer assays and GC–MS analysis showed that although red-rot-infected plants released a different volatile blend from mock-inoculated, the wasps showed no preference for either of the two treatments. Red-rot disease also caused qualitative and quantitative changes in the volatile blend emitted by herbivore-damaged plants relative to healthy and damaged plants, such as the addition of the fungal-derived 1-octen-3-ol and either a reduction or an increase of volatiles. These differences were detected by C. flavipes, which preferred volatiles released by herbivore-damaged healthy over herbivore-damaged infected plants. When given a choice between mock-inoculated and herbivore-damaged infected plants, the wasps preferred infected ones. Sugarcane-borer larvae were larger when fed on healthy plants relative to red-rot infected sugarcane plants, indicating that parasitoid wasps likely benefit from being attracted to volatiles of healthy over infected damaged sugarcane. Although the infection did not seem to disrupt the parasitoid host-location, red-rot disease attenuates the attractiveness of herbivore-induced sugarcane volatiles to C. flavipes.