D3101: Battle of the bites: How fall armyworm secretions shape sorghum defenses

Plants have evolved complex defense mechanisms against insect herbivory. While feeding, chewing insects release two kinds of oral cues: oral secretions (OS=regurgitant) and saliva. These cues have the ability to reprogram the plant defenses. Flavonoids, which are major plant secondary metabolites, provide defense against feeding by fall armyworm (FAW; Spodoptera frugiperda), which is an important chewing insect pest on many crops, including sorghum (Sorghum bicolor). Previously, it has been shown that sorghum flavonoids are required to provide resistance to FAW. Here, we monitored the role of FAW oral cues in modulating sorghum flavonoid-based defenses. Our results indicate that FAW OS induced the expression of genes related to flavonoid biosynthesis and total flavonoids, thereby enhancing sorghum’s defense against FAW larvae. Conversely, FAW saliva suppressed the flavonoid-based defenses and promoted FAW caterpillar growth. Thus, we infer that different oral cues in FAW may have contrasting roles in altering sorghum defenses. These findings expand our understanding of the precise modes of action of caterpillar oral cues in modulating plant defenses and help design novel pest management strategies against FAW in this vital cereal crop.