The nature and distribution of Ostrinia nubilalis (Hubner) oviposition and its feeding behavior was investigated on cotton. Field results show that seventy-seven percent of the petiole damage occurred on the lower portions of lateral stems and in the middle and upper portions on the main stem. Seventy-one percent of the stem damage occurred on the main stem and forty-two percent in the middle of this stem. Fifty percent of the boll damage was on one and one half inch bolls, thirty-nine percent on one inch bolls, and ten percent on one-half inch bolls. Sixty percent of the plants examined were damaged for a total of 151 instances of damaged plant parts. For the entire study, only three egg masses were located on 100 plants. In addition to field observations, egg masses were collected from a laboratory colony which had been established from a field population and placed on cotton plants at selected sites. First and second instar larvae which had hatched from egg masses placed on the undersurface of leaves or stems first fed on the leaf veins and midrib, feeding on the surface under a protective silken web for 8 to 12 days. As larvae reached the late second and third instars, they migrated to and bored into petioles and succulent lateral stems. Later instars then moved to larger plant parts to complete larval development. When egg masses were placed on bolls, first instar larvae immediately moved under the bract and fed on the fleshy calyx. Later instars then bored into the bolls to complete development. A limited study was undertaken to identify the fungi associated with infested bolls. The predominant fungi isolated were Alternaria sp., Cephalosporium sp., and Fusarium spp., all of which have been identified as common boll rot organisms.