Plant defense against insect herbivory: Flavonoid-mediated growth inhibition of Helicoverpa zea

Plant biotic stressors, including insect damage to economically important crops, are on the rise because of climate change (Skendžić et al., 2021; Matzrafi, 2019; Hatfield et al., 2011). Corn earworm (CEW) Helicoverpa zea (Boddie) is one of the economically important insect pests of maize (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench). In this study, maize near-isogenic lines with high flavonoid content in silks, husks, and kernel pericarps were used to test against the survival of CEW larvae. Larvae feeding on high-flavonoid maize lines had increased mortality and reduced body weight. These larvae showed leakage of the midgut peritrophic matrix, indicating leaky-gut-like syndrome suggesting involvement of microbiome changes in the larval gut. Moreover, the expression of chitin formation and gut health-related genes was changed in the midgut of larvae consuming the flavonoid-rich husks. CEW herbivory caused high and localized accumulation of flavonols around the damaged husk area. Silks and husks of high flavonoid lines also had elevated levels of 3-deoxyanthocyanidins (3-DAs) and flavan-4-ols, which contributed to increased larval mortality. Feeding assays using an artificial diet supplemented with a sorghum 3-DAs-rich extract further confirmed the efficacy of these flavonoids in increasing larval mortality. Altogether, this study suggests a novel option for integrated pest management for CEW larvae.