View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Valparaiso University The Great Lakes Entomologist Volume 47 Numbers 3 & 4 - Fall/Winter 2014 Numbers 3 & Article 3 4 - Fall/Winter 2014 October 2014 Establishment, Impacts, and Current Range of Spotted Knapweed (Centaurea Stoebe Ssp. Micranthos) Biological Control Insects in Michigan B. D. Carson Michigan State University C. A. Bahlai Missouri State University D. A. Landis Michigan State University Follow this and additional works at: https://scholar.valpo.edu/tgle Part of the Entomology Commons Recommended Citation Carson, B. D.; Bahlai, C. A.; and Landis, D. A. 2014. "Establishment, Impacts, and Current Range of Spotted Knapweed (Centaurea Stoebe Ssp. Micranthos) Biological Control Insects in Michigan," The Great Lakes Entomologist, vol 47 (2) Available at: https://scholar.valpo.edu/tgle/vol47/iss2/3 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at [email protected]. Carson et al.: Establishment, Impacts, and Current Range of Spotted Knapweed (<i 2014 THE GREAT LAKES ENTOMOLOGIST 129 Establishment, Impacts, and Current Range of Spotted Knapweed (Centaurea stoebe ssp. micranthos) Biological Control Insects in Michigan B. D. Carson1, C. A. Bahlai1, and D. A. Landis1* Abstract Centaurea stoebe L. ssp. micranthos (Gugler) Hayek (spotted knapweed) is an invasive plant that has been the target of classical biological control in North America for more than four decades. Work in the western U.S. and Canada has shown the seedhead-feeding weevils Larinus minutus Gyllenhal and Larinus obtusus Gyllenhal (Coleoptera: Curculionidae) and the root-boring weevil Cyphocleonus achates (Fahraeus) (Coleoptera: Curculionidae) to be the most effective C. stoebe control agents. These three weevils have recently been introduced into the eastern U.S., including sites in Michigan in 2007 and 2009. In 2010, we made additional releases at six sites in Michigan, monitoring them for three years 2011-13. Here we report on the establishment, impact, and cur- rent range of L. minutus, L. obtusus, and C. achates in Michigan. We also report on the initial results of native plant overseeding treatments that were applied to biological control release sites with the aim of supplementing the nectar source C. stoebe provides. We found that L. minutus has established at all of its Michigan release sites and is widespread in the southwestern part of the state, while L. obtusus has established at the single site where it was released in 2007 and is spreading to adjoining counties. We also found C. achates to be present at four sites and established at one additional site in Michigan, but in all cases abundances are low and dispersal has been minimal (< 10 m). In the three years following the 2010 releases, we found no measurable impacts of these biological control agents on C. stoebe growth, demographics, or plant community metrics. We also found little evidence of native flowering plant establishment at seeded sites. These baseline data will be useful in monitoring the spread and potential impacts of biological control agents on C. stoebe in Michigan. ____________________ Centaurea stoebe L. ssp. micranthos (Gugler) Hayek (spotted knapweed) is an herbaceous plant native to southern and eastern Europe. In its home range, the species occurs at relatively low densities and is well integrated into grassland communities (Sheley et al. 1998). In contrast, C. stoebe is considered highly invasive in North America and frequently becomes the dominant species in grassland, rangeland, and old field habitats. Populations ofC. stoebe are now found throughout much of the continental United States, with the exceptions of Texas, Oklahoma, and Mississippi (USDA 2013). Long considered a pest in western U.S. rangelands, it is estimated that C. stoebe costs ranchers as much as $155 million in annual gross revenue in Montana alone (Griffith and Lacey 1991). Infestations of C. stoebe have also been shown to cause dramatic decreases in plant diversity, ecosystem functioning, and utilization of land by wild and domesticated foraging animals (Watson and Renney 1974, Hakim 1979, Lacey et al. 1989, Sheley et al. 1998, Mummey and Rillig 2006). More recently, C. stoebe has also become a serious invader in the eastern and midwestern U.S., 1 Michigan State University, Department of Entomology, 204 CIPS, 576 Wilson Road, East Lansing, MI 48824. *Corresponding author: (e-mail: [email protected]). Published by ValpoScholar, 2014 1 The Great Lakes Entomologist, Vol. 47, No. 2 [2014], Art. 3 130 THE GREAT LAKES ENTOMOLOGIST Vol. 47, Nos. 3 - 4 threatening the ecological integrity of natural areas. In Michigan, C. stoebe has been documented as an invader of rare native ecosystems, including dry sand and dry-mesic prairies (Kost 2004), mesic sand prairies (Kost and Slaughter 2009), dry-mesic southern forests (Lee 2007), oak barrens (Cohen 2001), oak-pine barrens (Cohen 2000), and open dunes, where it is often considered a primary threat to biodiversity (Albert 1999). At the Pictured Rocks National Lakeshore in northern Michigan, Marshall and Storer (2008) found that C. stoebe invasion of open dune habitats had adverse effects on native plant communities and altered insect community composition. Despite the efforts of land managers, conventional control methods, in- cluding herbicides and mowing, have not adequately controlled the spread of C. stoebe. In the U.S., western states, notably Montana, Colorado, and Wash- ington, have spearheaded the effort to use classical biological control to slow and reverse the invasion of C. stoebe and Centaurea diffusa (diffuse knapweed) (Watson and Renney 1974, Story and Anderson 1978, Sheley and Jacobs 1997, Corn et al. 2009). More recently, agencies in the eastern U.S. have begun making their own biological control releases targeting C. stoebe (http://www.biocontrol. entomology.cornell.edu/weedfeed/Larinus). Biological control of C. stoebe in Michigan began with the release of two spe- cies of seedhead flies,Urophora affinis Frauenfeld and Urophora quadrifasciata Meigen (Diptera: Tephritidae) in Isabella County in 1994 by USDA APHIS PPQ. Subsequent surveys in 1998-2000 detected U. quadrifasciata in all 83 Michi- gan counties and U. affinis in 24 counties (Lang et al. 2001). A 2009 survey by Landis and Sebolt (unpub. data) showed that both seedhead flies remain widely established in both peninsulas in Michigan. While seedhead infestation rates in Michigan are high (U. quadrifasciata averaged 78.1% and U. affinis averaged 52.5% in 2009), C. stoebe densities also remain high, confirming the reported inef- ficiency of these two agents in controllingC. stoebe (Myers et al. 2009). The introduction history of the two seedhead-feeding weevils and root- boring weevil for biological control of C. stoebe in Michigan is complex. Based on the request of commercial biological control agent suppliers, in 2007, USDA- APHIS issued permits for the interstate transport of the root-boring weevil Cyphocleonus achates (Fahraeus) (Coleoptera: Curculionidae) and the two seedhead-feeding weevils, Larinus minutus Gyllenhal, and Larinus obtusus Gyllenhal (Coleoptera: Curculionidae), into Michigan. Releases of these insects were subsequently made at two sites in southern Michigan by private and public land managers (Table 1). However, due to the concerns of commercial beekeepers in Michigan, who value C. stoebe as a midsummer nectar source, further issuance of biological control agent release permits was suspended in 2008. In 2009, the USDA-Forest Service requested and received a permit to conduct controlled releases of C. achates and L. minutus in the western part of Michigan’s Upper Peninsula. While performing preliminary searches for C. stoebe biological control insects in 2011, we unexpectedly found L. minutus in two Michigan counties near the Indiana border, ca. 60 km from any known Michigan release sites. After additional investigation, we discovered that the Indiana Department of Natural Resources had made releases of L. minutus and C. achates in Bristol, Indiana, at a site 2.5 km from the Michigan border (Van Driesche et al. 2002). These releases were made in 1996, and we concluded that they are the most likely source of the L. minutus population occurring in southwestern Michigan (Carson and Landis, in review). Following the 2007 and 2009 Michigan releases, interest in C. stoebe bio- logical control increased, and the Michigan Department of Natural Resources (MDNR) contracted with Michigan State University to establish biological control research sites on MDNR lands. In 2010, we made releases at six MDNR managed sites in Michigan, monitoring them for agent establishment and https://scholar.valpo.edu/tgle/vol47/iss2/3 2 Published byValpoScholar, 2014 2014 Table 1. Sites and species of C. stoebe biological control weevils released in Michigan and bordering states. These include a 1997 release made by the Indiana DNR, two 2007 releases made by private landholders, a 2009 release made by the USFS, and six 2010 releases made by MSU. Carson etal.:Establishment,Impacts,andCurrentRangeofSpottedKnapweed(<i Year of Larinus Larinus Cyphocleonus Site Name County Release minutus obtusus achates Longitude Latitude Elkhart (Indiana) 1996 + - + W85.77141 N41.73578 THE GRE Lake Orion Oakland 2007 + - + W83.29482 N42.75865 Kalamazoo Kalamazoo 2007 - + + W85.76245 N42.28951 ENTOMOLOGIST LAKES AT Iron, Gogebic, Ottawa National Houghton 2009 + - + Not available Not available Seney North Schoolcraft 2010 + - + W86.04817 N46.34626 Seney South Schoolcraft 2010 + - + W86.05508 N46.34072 Camp Grayling Crawford 2010 + - + W84.62825 N44.78453 Houghton Lake Roscommon 2010 + - + W84.89275 N44.31051 Flat River Ionia 2010 + - + W85.21220 N43.12400 Sharonville Jackson 2010 + - + W84.14593 N42.19637 131 3 The Great Lakes Entomologist, Vol. 47, No. 2 [2014], Art. 3 132 THE GREAT LAKES ENTOMOLOGIST Vol. 47, Nos. 3 - 4 impact for three years during 2011–13.