Third instar hop vine borer (Hydraecia immanis) and potato stem borer (H. micacea) are new pest species on corn in the Midwest. Early instar larvae feed on small-stemmed grasses, and later instar larvae switch to broad- stemmed hosts to complete development. In order to assess potential suitability of various weeds of corn fields, larvae were reared on seven selected broad- leaved plants for 16-18 days under greenhouse conditions to determine their feeding behavior and performance. Domestic plants included hop (Humulus lupulus) and potato (Solanum tuberosum); weed species included curly dock (Rumex crisp us), redroot pigweed (Amaranthus retroflexus), lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia) and giant ragweed (A. trifida). Larvae of both species survived best on corn, hop, and curly dock. While potato was an excellent host for the potato stem borer H. micacea, survival was poor for the hop vine borer, H. immanis. Red root pigweed, common ragweed, giant ragweed and lambsquarters were poor hosts for both moth species. While the potato stem borer, H. micacea, larvae were able to grow well and gain weight rapidly on several hosts, the hop stem borer, H. immanis, grew well only on hops. Larval feeding behavior and size, as well as plant phenology, stem thickness, and growth form, are all critical determinants as to whether or not a particular plant species can serve as a final host on which H. immanis and H. micacea can complete development
