At Konza Prairie, Kansas, milkweeds (Asclepias viridis) were mapped and censused repeatedly to examine the influence of neighboring conspecifics on colonization of individual host plants by adults of the seed bug Lygaeus kalmii. Analysis by multiple regression suggests that the primary determination of abundance of adult bugs on a host plant was the plant's own pod (seed) production; abundance of adult bugs also increased, however, with increasing pod production by adjacent plants. This neighborhood effect was limited to plants immediately adjacent to a host plant; pod density greater than 3 m distant from hosts had little influence on colonization of hosts by bugs. Mark-recapture studies revealed differences in responses of the two sexes of L. kalmii to neighboring pod density, males lingered longer, while females lingered less on individual plants when these plants were surround by many vs fewer pods. Damage from L. kalmii sustained by milkweeds, thus result from a complex interplay of reproductive behaviors of individual host plants, their neighbors, and their seed predators. (Key words: Asclepias viridis, host plant colonization, host plant dispersion, insect mark-recapture, insect/plant association, Lygaeus kalmii, milkweed, tallgrass prairie)