Distribution and Status of Silphium Herb Gall Wasps (Cynipoidea: Aulacideini: Antistrophus) and their Associated Endophytic Communities in Wisconsin

At least six described species of the herb gall wasp genus Antistrophus Walsh (Hymenoptera: Cynipoidea: Aulacideini) are dependent on the plant genus Silphium L., a plant group emblematic of now-endangered Midwestern tallgrass prairies. The distribution and conservation status of Antistrophus gall wasps is mostly a mystery, and these insects have only recently been recorded from Wisconsin. We surveyed the state for Antistrophus gall wasps on four Silphium species, whole-leaf rosinweed (S. integrifolium Michx.), compass plant (S. laciniatum L.), cup plant (S. perfoliatum L.), and prairie dock (S. terebinthinaceum Jacq.) to determine their distribution and abundance in Wisconsin. We report new state records for several Antistrophus species and confifirm the identity of A. bicolor Gillette as inducing galls in the flflowers of S. integrifolium. We also report the fifirst published records of Antistrophus gall wasps inducing galls in the leaves of S. laciniatum and S. terebinthinaceum, Antistrophus inducing imperceptible, hidden galls in the stems of S. integrifolium, and Antistrophus inducing galls in the flflowers of S. terebinthinaceum and S. perfoliatum. We found flflower galls in S. perfoliatum in only 10% of surveyed populations; should these individuals prove to comprise a distinct species, it could warrant listing as a Species of Greatest Conservation Need (SGCN), if not listing as Threatened. Additionally, terminal stem galls induced by Antistrophus silphii Gillette were found in only 25% of surveyed S. integrifolium and S. perfoliatum populations, and in only low numbers when present; these fifindings resulted in its listing as a SGCN in 2016. Tumbling flflower beetles (Coleoptera: Mordellidae) were found in 13% of collections, one checkered beetle (Coleoptera: Cleridae), Enoclerus rosmarus [Say]) was found, and at least 14 species of non-Antistrophus wasps (Hymenoptera), mostly likely all parasitic, were found in 87% of collections. These include the genera Aprostocetus, Baryscapus, Brasema, Chorebus, Eupelmus, Eurytoma, Heterospilus, Homoporus, Neocatolaccus, Ormyrus, Schizoprymnus, and Quadristichus. Overall, communities associated with Silphium in Wisconsin are shown to be highly diverse and in need of further study, especially substantiating the species identities of the many endophytic insects associated with these plants.