ABSTRACT We describe the development, selection, and application of a monoclonal antibody (MAb) to eggs of pink bollworm, Pectinophora gossypiella (Saunders). We tested this MAb against all pink bollworm life stages and the egg stage of 10 other insect species using an enzyme-linked immunosorbent assay (ELISA). In all cases, the MAb was highly specific to pink bollworm egg and adult female antigens. A Western blot analysis showed that the MAb reacted with two egg polypeptides with molecular weights between 46 and 60 kDa. Predation studies were conducted in the laboratory to test the usefulness of this MAb for studying predator-prey interactions. Most predators fed either one or two pink bollworm eggs responded positively to the MAb in a serological analysis of gut contents. These data suggest that this MAb can be used as a diagnostic probe for gut content analysis of potential predators of pink bollworm eggs under field conditions.