Fungal Endophyte Seed Treatments Enhance Defensive Volatile Emissions and Alter Stink Bug Olfactory Preference

Piercing-sucking insects that were once considered secondary pests are now a primary cause of cotton yield loss. Pests with piercing-sucking mouthparts are unaffected by current Bt toxins and require alternate control measures. We are researching the effects of manipulating the phytobiome, the microbial community in and around a plant, on mitigating sucking bug damage to cotton. We treat our seeds with the spores of fungi known to be endophytes of cotton, fungi that live asymptomatically within healthy plant tissues which we cultured from surface sterilized plant cuttings. Previous experiments in our lab demonstrated that two species of sucking bugs were significantly deterred from feeding on the reproductive structures of treated plants and the behavior of the insects suggests volatile emissions from the plants might play a role in this deterrence. We analyzed the constitutive (no herbivore present) and induced (herbivore present) volatile emissions from individual leaves of fungal-treated and untreated cotton plants using solid-phase micro-extraction and gas chromatography to mass spectrometry (SPME GC-MS). We used the foliar-feeding beet army worm, Spodoptera exigua, to examine if the experimental phytobiome manipulations affected the way cotton plants responded to herbivory through volatile emissions. Our results suggest that the fungal treatment triggers defensive priming in the plants, producing an enhanced volatile response compared to control plants. Additionally, we tested the olfactory preference of the southern green stink bug, Nezara viridula, towards greenhouse-grown treated and untreated plants using a Y-tube olfactometer, the results of which suggest a constitutive effect of the treatment on volatile emissions.