Girdle and plant part associations of threecornered alfalfa hopper nymphs (Homoptera : Membracidae) on soybean

Plant part and girdle associations of Spissistilus festinus (Say) instars on soybean, Glycine max (L.) Merrill, were investigated by inspecting randomly selected whole plants. Locations of many nymphs changed from stem to nonstem stmctures as plant development increased and later back to stem structures as lateral branches became available. Third to fifth instars preceded first and second instars in these changes. A large proportion (≥39%)of nymphs was associated with main stems regardless of plant phenology. Association of nymphs with plant reproductive structures was least (2%) during blooming and greatest (13%)during pod fill. Association of nymphs with stem and petiole girdles increased with nymphal age. Also, a greater proportion of older nymphs was oriented above girdles. Girdle association was higher for nymphs on leaves and petioles than for those on stems, but most nymphs were not associated with girdles. The absence of differences in associations of S. festinus instars with reproductive structures contrasted with the differences observed in associations with girdles, suggesting that the factors responsible for nymphal association with the two types of structures may differ.