Stethobaris ovata (LeConte)

Dunford, James C., Young, Daniel K. & Krauth, Steven J., 2006, Stethobaris ovata (LeConte) (Curculionidae) on Eastern Prairie Fringed Orchid [Platanthera leucophaea (Nuttall) Lindley] in Wisconsin, The Coleopterists Bulletin 60 (1), pp. 51-52 : 51-52

Stethobaris ovata (LeConte) ( Curculionidae ) on Eastern Prairie Fringed Orchid [ Platanthera leucophaea (Nuttall) Lindley ] in Wisconsin

Weevils in the genus Stethobaris LeConte are commonly referred to as orchid weevils since all known plant associations belong to the Orchidaceae ( Brown 1966) . Stethobaris commixta Blatchley has been recorded on both the federally threatened western prairie fringed orchid, Platanthera praeclara Sheviak & Bowles (Hull Sieg and O’Brien 1993; Cuthrell 1994), and the federally threatened eastern prairie fringed orchid, Platanthera leucophaea (Nuttall) Lindley (Cuthrell 1994) . To our knowledge this note constitutes the first record of Stethobaris ovata (LeConte) on the eastern prairie fringed orchid (EPFO). This note also provides the first published record for S. ovata in Wisconsin (new state record).

EPFO occurs in remnant, mesic prairie sites concentrated in Wisconsin, Illinois, Michigan, and Ohio. Due to habitat loss, the distribution of EPFO has declined to approximately 70% of original site records (Bowles 1993). To begin to determine the status of remaining populations and whether pollinator presence affects EPFO reproduction, a survey was conducted during the summer of 1999 in Wisconsin (where EPFO is listed as endangered) to create a list of insects observed on EPFO and to identify potential pollinators (Crosson et al. 1999).

Orchids were monitored at five sites in southern Wisconsin for a total of 221.5 hours. Observations confirmed Lepidoptera pollinators from the family Sphingidae for Platanthera spp. recorded in the literature (Sheviak and Bowles 1986; Westwood and Borkowsky 2004). Additionally, a number of other insects, including S. ovata , were observed on EPFO. Stethobaris ovata individuals were observed moving about the entire plant, especially in the leaf folds at the juncture of the leaf and stem. They were also observed in the flower heads at various times of the day and several individuals had one or more pollinia attached to the head and thorax. A few weevils were observed feeding on orchid buds. Seven weevils were sampled and sent to Charles W. O’Brien for confirmation of species determination. These individuals were deposited as vouchers in the University of Wisconsin Insect Research Collection.

Species of Stethobaris have been recorded consuming various orchid parts such as buds, leaves and roots (Hull-Sieg and O’Brien 1993; Cuthrell 1994; Downie and Arnett 1996). Howden (1995) recorded S. ovata on several orchids, including Corallorhiza striata Lindley, C. trifida Chat. var. verna (Nutt.) Fem. , Cypripedium spp. , Epipactis helleborine (L.) Crantz, and Habenaria spp. St. Hilaire (2002) reported that S. ovata feeds on orchid flowers and oviposits in the stems and fruits of Epipactis spp. and Cypripedium spp. orchids in New England where it is considered a pest by reducing seed yield. Judd (1979) recorded S. ovata feeding on E. helleborine in Ontario, resulting in the blackening and withering of the plant.

The overall impact of S. ovata on EPFO or whether its presence is consistent each year at EPFO sites in Wisconsin remains unknown. No attempt was made to calculate total numbers of S. ovata on EPFO during this survey. Further quantitative research, morphological analysis, and empirical evidence would be needed to determine whether floral morphology would allow Stethobaris adults to affect reproductive success. Other potential impacts of the weevil’s biology such as feeding behavior should also be investigated to better understand the evolutionary relationship it has with this rare orchid.