WETLANDS, Vol. 19, No. 1, March 1999, pp. 220-227 © 1999, The Society of Wetland Scientists RESPONSE OF INVERTEBRATES TO GLYPHOSATE-INDUCED HABITAT ALTERATIONS IN WETLANDS George M. Linz 1, William J. BleieF, John D. Overland 2.~, and H. Jeffrey Homan l U. S. Department of Agriculture, National Wildlife Research Center Great Plains FieM Station Bismarck, North Dakota, USA 58501 '- Department of Zoology, Stevens Hall North Dakota State University Fargo, North Dakota, USA 58105 Present address: 3Minnesota Environmental Consulting, Inc., 1731 Graydon Ave. Brainerd, Minnesota, USA 56401 Abstract: Wetlands in the Prairie Pothole Region of eastern North Dakota, USA are often overgrown with cattails (Typha spp), providing habitat for crop-depredating blackbirds and impeding use by waterfowl. One and two years post-treatment (1992 and 1993), we assessed the response of invertebrates to a catastrophic reduction in cattail coverage caused by glyphosate, a herbicide apptied to about 14,000 ha of North Dakota's wetlands since 1991. Numbers of Crustacea, Hydracarina, O1igochaeta, Copepoda, Ostracoda, and Cladocera were similar between treated and reference wetlands (P > 0.10), while abundance of Gastropoda was greater in the treated wetlands (P = 0.10). Insect abundance was greater in treated wetlands (P < 0.01), with activity traps yielding highest numbers in July. Corixidae and Chironomidae were more abundant in treated wetlands (P < 0.10), whereas Chaoboridae was consistently more plentiful in the reference wetlands (P = 0.05). Our results suggest that populations of some aquatic invertebrates may be enhanced by a reduction in cattail coverage with glyphosate-based herbicide. Key Words: aquatic insects, cattails, ducks, glyphosate, habitat management, invertebrates, waterfowl, wet- lands INTRODUCTION Historically, wetland vegetation in North Dakota, USA consisted of sparse stands of bulrush (Scirpus spp.) and common cattail (Typha latifolia) (Kantrud 1986). By the 1970s, narrow-leaved cattail (T. angus- tifolia L.), a species not recorded in North Dakota until 1942, had spread throughout the state (Kantrud 1986). These native and exotic cattails hybridized to produce T. × glauca Godron, a robust plant that quickly forms dense homogenous stands (Weller 1975, Davis and van der Valk 1978). Cattail-dominated wetlands deter use by waterfowl (Kantrud 1986, Linz et al. 1996) and attract migrating blackbirds, which may cause signifi- Cant amounts of crop damage (Leitch et al. 1997). Wet- land managers have controlled cattails by manipulating water levels, regulating muskrat (Ondatra zibethica) populations, grazing with livestock, buming, mowing, discing, excavating, and blasting with explosives (Kantrud 1986). In 1991, wildlife agencies began operational spray- ing of cattail-dominated wetlands in North Dakota with glyphosate-based herbicide (Homan et al. 1998). Good management practices dictate that herbicides must not have detrimental effects on aquatic inverte- brate populations, a critical food source for migrating and nesting wetland-dependent birds. Glyphosate, a nonselective, nonresidual, postemergent aquatic her- bicide inhibits protein synthesis by blocking the shi- kimic acid pathway (Ware 1989), which is absent in animals, rendering glyphosate practically nontoxic to aquatic invertebrates (Folmar et al. 1979, Buhl and Faerber 1989, Henry et al. 1994). Any potential neg- ative effects from glyphosate treatments are probably related to the introduction of large quantities of de- caying organic material (Solberg and Higgins 1993). Solberg and Higgins (1993) assessed the post-treat- 220