Nitrogen (N) is a limiting resource for both plants and animals. We expect that plant growth will be influenced by N availability and that life history parameters of herbivores will differ in response to plants grown under various N regimes. Cotton plants, Gossypium hirsutum, grown with low N availability were shorter and leaf N concentration was lower compared to those with high N level. Beet armyworm, Spodoptera exigua, development was affected by the N status of cotton plants on which they were reared. Fresh weight of caterpillars reared on cotton plant with lower N was consistently lower than those reared on high N cotton plants. Time to pupation and adult emergence of caterpillars grown on low N cotton plants were longer. The potential supernumerary development of beet armyworm due to low N was investigated. In this study, we also compared the life-time damage of caterpillars to cotton plants with different N levels.