Differences in first and second day barley, wheat, and oat induced volatiles in response to fall armyworm (Spodoptera frugiperda) herbivory

Plant volatile organic compound (VOC) induction commonly occurs after leaf injury, especially insect herbivory. However, VOC responses from different plant species are infrequently compared after herbivory by the same herbivore species, and responses of low VOC emitting grasses to herbivory tend not to be studied. We had fall armyworm larvae, Spodoptera frugiperda, feed on three barley, wheat, and oat leaves for 4 hrs, compared to two clipping treatments, and then measured VOC induction responses (ng g^-1 hr^-1) of these cereals at two post-injury intervals (6-12 and 30-36 hr post-introduction). Barley and wheat had more than 2x total VOC emission than oat at 6-12 hr, but only 1.5x greater than oat at 30-36 hr. Barley had 14 induced VOCs at the first measurement time, compared to 10 for wheat and 8 for oat. Also, while barley still had all induced VOCs but one (13) at the second measurement time, the number of induced VOCs at this time was < 50% for wheat (4) and oat (2). The most VOCs induced only by S. frugiperda herbivory, but neither clipping treatment, was also from barley at both measurement times (4 & 3) compared to wheat (2 & 0) and oat (0 & 0). Finally, barley had 4 induced VOCs not even reliably detected from the other two cereals, wheat had 2, and oat had none. In several ways, barley had the strongest VOC induction, wheat was intermediate, and oat was weakest, in response to the same generalist herbivore. Future studies would need to examine whether these interspecific cereal VOC induction responses lead to differential natural enemy attraction and/or future herbivore deterrence, among the test cereals and if barley has the strongest VOC responses to other chewing herbivores and other herbivore feeding guilds.