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Plant-insect interactions are of profound importance in agriculture. Herbivorous insects can inflict substantial damage to susceptible plants. Thus understanding the mechanisms of plant tolerance to herbivory can lead to breeding resistant plants. Although this area has been studied for many years, we are still largely unaware of the plant-related biochemical changes that result in tolerance or resistance mechanisms. This paucity of data is further complicated by the great range of insect herbivores and in several cases by an almost complete lack of molecular and biochemical information of the agronomically important plant species. We investigated the role of plant proteins and some oxidative enzymes in the defense response of buffalograss, Buchloë dactyloides (Nuttall) Engelmann, to the chinch bug, Blissus occiduus Barber. Changes in catalase and peroxidase activity were observed in both resistant and susceptible buffalograsses in response to chinch bug feeding. Susceptible plants were shown to have a lower level of catalase activity when compared to their respective control plants. By contrast, catalase activities of resistant plants were similar between infested and control buffalograsses throughout the study. Resistant plants had higher levels of peroxidase activity when compared with their control plants, while peroxidase activities for control and infested susceptible plants remained at similar levels or were slightly lower for infested plants. These findings suggest that chinch bug feeding leads to a loss in catalase activity in susceptible buffalograsses. In contrast, resistant buffalograsses may be able to tolerate chinch bug feeding by increasing their peroxidase activity.