Anthocyanin levels mediates fall army worm (Spodoptera frugiperda) incidence and defenses in green and purple cabbage (Brassica oleracea var. capitata)

Anthocyanins, one of the major groups among polyphenols, play well documented role in plant pigmentation and human health. However, it has been found that they can also act as chemical defenses in plants against insect herbivores, owing to their antioxidant activity. Here, through a series of field and lab-based assays, we examined whether the variation in anthocyanin levels can explain the herbivory of fall armyworm (Spodoptera frugiperda: Lepidoptera; FAW) in purple (Rio Grande Red) and green (Blue Vantage) cabbage (Brassica oleracea) varieties in an organic farming system in South Texas. Through extensive field observations over an entire growing season, we found out that FAW incidence and consequent damage is significantly higher on green cabbage during early season, when compared to purple cabbage. And spectrophotometry-based lab assays showed that purple cabbage had significantly higher levels of anthocyanins than green cabbage. Interestingly though, we also found contrasting results in late season where more FAW damage was observed on purple cabbage, although they had more anthocyanins. We speculate that in addition to anthocyanins that play a significant role in herbivore defenses, other chemical defenses including Brassicaceae specific secondary metabolites may also play a role in herbivore defenses, in a season and species dependent manner.