As plants participate in gene-for-gene interactions with pathogens and insect pests, specific recognition events initiate plant responses that ultimately result in death or containment of the attacker. The complex networks of signal-transduction pathways that respond as plants react to the inflicted damage are poorly characterized for most plant interactions with insects. The first few days after egg hatch are critical for these recognition events in wheat interactions with Hessian fly, During this time, first-instar larvae are known to inject substances into wheat plants initiating events that either lead to resistance and larval death, or trigger the formation of microscopic gall like tissue at feeding sites in susceptible wheat plants. Wheat gene expression was quantified during both compatible and incompatible interactions with first-instar Hessian fly larvae in order to identify genes that contribute to plant resistance or susceptibility. A few well-known defense response genes were slightly up-regulated during resistance, but wound-induced and oxidative burst genes were unresponsive even though they are commonly involved in defense against other herbivorous insects or microbial pathogens. However, a robust up-regulation was seen for a unique set of salicylic acid-responsive genes that includes lectins and lipoxygenase. A gene similar to those encoding membrane pore-forming proteins was up-regulated in susceptible plants, and may be involved in making plant nutrients available for larval consumption.