Technical Abstract: Plant defense responses against insect herbivores frequently depend on the biosynthesis and action of jasmonic acid (JA) and its conjugates. To better understand JA signaling pathways in maize (Zea mays L.), we have examined two maize genotypes, Mp708 and Tx601. Mp708 is resistant to feeding by lepidopteran larvae and constitutively accumulates elevated levels of JA whereas the susceptible genotype Tx601 induces JA synthesis only in response to feeding. The constitutive expression of JA-related genes also is higher in Mp708 and Tx601 and larval feeding results in a large increase of OPDA accumulation in Mp708. In control and infested Mp708 plants salicylic acid (SA) levels are lower than those in Tx601 suggesting that SA and JA have antagonistic effects on insect defense responses in these plants. The resistant genotype also displays exceptionally high expression of a lipoxygenase (LOX) gene whose product, hydroperoxy-linolenic acid, can be further metabolized into volatile aldehydes and alcohols. In response to herbivory Mp708 generates comparatively higher amounts of hydrogen peroxide and increased senescence is observed at feeding sites. The mechanisms involved in the induction, perception and transduction of JA signals into functional responses is not well understood in maize, particularly, at the midwhorl stage of growth when plants are vulnerable to lepidopteran damage. Although the molecular mechanisms regulating the constitutive accumulation of JA in Mp708 are unknown, this genotype may be valuable in studying signaling pathways that maize uses to respond to insect herbivores.