The Great Lakes Entomologist Volume 51 Numbers 3 & 4 - Fall/Winter 2018 Numbers 3 & Article 4 4 - Fall/Winter 2018 January 2018 Use of Spotted Knapweed/Star Thistle (Asterales: Asteraceae) as the Primary Source of Nectar by Early Migrating Monarch Butterflies (Lepidoptera: Nymphalidae) from Beaver Island, Michigan Matthew M. Douglas Grand Rapids Community College and the University of Kansas, [email protected] Follow this and additional works at: https://scholar.valpo.edu/tgle Part of the Entomology Commons Recommended Citation Douglas, Matthew M. 2018. "Use of Spotted Knapweed/Star Thistle (Asterales: Asteraceae) as the Primary Source of Nectar by Early Migrating Monarch Butterflies (Lepidoptera: Nymphalidae) from Beaver Island, Michigan," The Great Lakes Entomologist, vol 51 (2) : 35-41 Available at: https://scholar.valpo.edu/tgle/vol51/iss2/4 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]. Use of Spotted Knapweed/Star Thistle (Asterales: Asteraceae) as the Primary Source of Nectar by Early Migrating Monarch Butterflies (Lepidoptera: Nymphalidae) from Beaver Island, Michigan Cover Page Footnote I would like to thank Brandy Van Zalen for her photography; Dr. Pamela Laureto of Grand Rapids Community College for her careful review; and the following for their observations and input into this paper: Dr. R. Haack and Dr. B. Leuck. This peer-review article is available in The Great Lakes Entomologist: https://scholar.valpo.edu/tgle/vol51/iss2/4 Douglas: Use of Star Thistle by Migrating Monarchs from Beaver Island, MI 2018 THE GREAT LAKES ENTOMOLOGIST 35 Use of Spotted Knapweed/Star Thistle (Asterales: Asteraceae) as the Primary Source of Nectar by Early Migrating Monarch Butterflies (Lepidoptera: Nymphalidae) from Beaver Island, Michigan Matthew M. Douglas Grand Rapids Community College (e-mail: [email protected]) ABSTRACT Recent observations over the past decade suggest that the invasive star thistle (aka spotted knapweed (Asterales: Asteraceae Centaurea stoebe L.) provides much of the nectar that supports monarch butterflies (Lepidoptera: Nymphalidae Danaus plexippus L.) in their pre-migratory and early migratory flight from the Beaver Island archipelago, an isolated chain of islands located in northern Lake Michigan. With the advent and continuation of global climate change, the opportunistic evolutionary changes that may take place between migrating monarchs and their dependence on non-native nectariferous plants, prior to migration, is worth further documentation and examination. Keywords: monarch migration, Danaus plexippus, star thistle, spotted knapweed, Centaurea stoebe, pre-migration nectar resources The eastern cohort of monarchs (Da- pine forest at 10,000 feet), and the en masse naus plexippus L.)—residing largely east of spring reproductive effort, which takes place the Rocky Mountains—exhibits an extended prior to the spring remigration northward. migratory period, somewhat variable in The natal origins of eastern North timing and success from year to year, but American migratory monarch butterflies temporally wave-like in occurrence, and that overwinter in Mexico have recently been most pronounced between 15 August and 15 October (Brower 1995). The success of identified, at least to general geographic the migration is dependent upon viable areas. A full 38 percent migrate to Mexico nectar-bearing plants (Brower et al. 2006), from the “Midwest;” however, their origins as well as ambient temperatures above 10°C are spread widely across a breeding range with enough radiant insolation, to warm the that extends across southern Canada and thorax to the minimal temperature required the northern tier states of the United States. for the butterflies to conduct continuous, University of Guelph scientists analyzed controlled flight (Douglas 1979). more than 1,000 samples from butterflies collected from the 1970’s onward to deter- One of the critical parameters en- mine their natal region. Approximately 17 suring successful migratory flight is the percent originated from the north-central availability of nectar-bearing plants from states, including Michigan and Ontario, which the adults feed, and from which they which represented the greatest number extract and convert sugars into fat reserves of butterflies for any specific natal region (Brower et al. 2006). Without sufficient food (Flockhart et al. 2017). reserves, migratory monarchs often die in the overwintering roosts located in the state This observational study should serve of Michoacan, Mexico. (Brower et al. 2012, as a heuristic attempt to establish whether Pleasants & Oberhauser 2012, Flockhart et or not migratory monarchs from the north- al. 2013; Flockhart et al. 2015, personal ob- ern tier states will ultimately switch to the servation February 2002). Thus, the ability invasive star thistle as a more reliable source to find nectar-bearing plants by sequential of nectar during the early migratory season generations of late summer and fall but- (Fig. 1). terflies migrating from southern Canada provinces and the northern tier states of the Materials and Methods United States to Mexico is critical to their survival. The extraction of sugars from late Study Location and Period of Study. summer and fall nectariferous plants is vital In previous years of observation, from 2010 to their successful migration, survival in the through 2016, and especially during the overwintering roosts (located within oyamel/ late summer days of 2017, monarchs were Published by ValpoScholar, 2018 1 The Great Lakes Entomologist, Vol. 51, No. 2 [2018], Art. 4 36 THE GREAT LAKES ENTOMOLOGIST Vol. 51, Nos. 3–4 Figure 1: Central Michigan University Biological Station on Sandy Bay, Beaver Island. Star thistle is shown in foreground. The invasive star thistle has established extensive populations along the swales and parabolic dunes running the circumference of the island. Photo credit: Brandy Van Zalen. observed nectaring almost exclusively on tion in many states. In northern Michigan, star thistle, also known vernacularly as however, many beekeepers are opposed to spotted knapweed (Centaurea stoebe L.) efforts directed at its eradication because a that dominates the swales and parabolic significant portion of their yearly revenue de- dunes throughout Beaver Island, part of a pends upon it, especially during late July and small archipelago of nine islands located August, when it is one of the few extensively in Lake Michigan, about 45 km due west of blooming plants in the northern Lower Pen- Charlevoix, Michigan at latitude 45.67 N, insula of Michigan and along Lake Michigan and longitude 85.55 W. It measures 145 km2 lakeshore (honeytraveler.com). According to (about 60 square miles). Just north of Beaver this source, star thistle honey has a light, Island resides Hog Island with a “natural transparent and thick viscous appearance state” flora of nearly 93 percent (Whately et with “an aroma of anise/almonds, slightly al. 2005) and thus most of the flora is native sharp or pungent with notes of sweet, spicy and, in a few cases, endemic, leaving this cinnamon, molasses and prune.” isolated ecosystem of Lake Michigan islands The star thistle first invaded the relatively untouched by invasive species, Beaver Island archipelago in the 1980’s, save for the shoreline environments. This became firmly established in the mid-1990’s, observational study has been conducted over and now can be found throughout the entire a number of years at Sandy Bay, in front of island, wherever there is appropriate habitat the Central Michigan University Biological (B. Leuck personal communication 2018). Station on Beaver Island. During mid-and There are approximately 476 populations late August of 2017, an unusually large comprising nearly 84 hectares (210 acres) of population of monarch butterflies emerged star thistle now on Beaver Island (GEI con- and in the course of a week assumed typical sultants 2017). Of 16 listed invasive species migratory behavior (Fig. 2). on Beaver Island, the invasion of star thistle History of Star Thistle in Michigan. is the largest, and except for Bladder Cam- Star thistle, a Central European native pion (Silene vulgaris (Moench) Garcke) at 70 with an estimated introduction in western hectares (175 acres), all other invasives can North America in the 1890s, is an invasive be measured at well under 16 hectares (40 plant that is currently the target of eradica- acres), and typically fewer than 4 hectares https://scholar.valpo.edu/tgle/vol51/iss2/4 2 Douglas: Use of Star Thistle by Migrating Monarchs from Beaver Island, MI 2018 THE GREAT LAKES ENTOMOLOGIST 37 Figure 2: Star thistle population extending along the swales and parabolic dunes of Beaver Island. Newly emergent monarch butterflies spend over a week exclusively nectaring at the flowers, prior to the first (“early”) wave of monarch migration from the island at the end of August. Monarch butterflies are now found on the island well into late October. Photo credit: Brandy Van Zalen. (10 acres). Despite this recent and successful grating southward down the western shore invasion, there has apparently not been any of Lake Michigan in August and September, significant change in the Solidago L. (gold- along with migrating monarchs. (In contrast, enrod) populations upon