The effects of disturbance on milkweed (Asclepias spp.), monarch butterflies (Danaus plexippus ), and monarch parasites.

Elisha K. Mueller and Kristen A. Baum

Department of Zoology, Oklahoma State University, Stillwater, OK 74078, United States

INTRODUCTION OBJECTIVES RESULTS CONTINUED

The effects of mowing on (Danaus Compare roadside and prairie sites for: Asclepias viridis was the most abundant monarch host plant in roadside and plexippus) habitat are unknown. Mowing removes the 1. OE and tachinid parasitism rates of monarchs. prairie sites, with < 1% of milkweed being A. tuberosa and A. stenophylla. aboveground portion of milkweed plants (Asclepias spp.), 2. Host plant density for monarchs. which could affect plant density and/or quality. The effects 3. Host plant quality (i.e., leaf toughness) for monarchs. Ascelpias spp. density: of roadside management on monarch butterflies and their 70 parasites are also unknown. Previous research has 60 MATERIALS AND METHODS identified that Ophryocystis elektroscirrha (OE) spore loads 50 are negatively correlated with migration distance and 40 30 increase throughout the breeding season (1, 2). Tachinid roadsides 20 ( archippivora) parasitism has also been identified Plants/transect prairies

as a significant source of mortality for monarch butterflies 10 0 (3). However, no studies have evaluated how mowing affects parasite loads. Roadside management and host plant disturbance may alter the dynamics of these Sampling period monarch-parasite interactions.  Study sites were selected along three roadsides and within three nearby prairies. A. viridis leaf toughness:  Fourth and fifth instars were collected and reared in the lab to quantify OE and tachinid parasitism rates. 400 350

 Asclepias density was quantified along 5m x 50m transects. 300  Leaf toughness was measured for Asclepias viridis using a 250 handheld penetrometer. 200 roadsides 150 prairies RESULTS toughness Leaf 100 50

OE parasitism rates: no infected monarchs were found for 0 May '11 June '11 May '12 spring 2012 (N=8, prairie sites; N=12, roadside sites) Sampling period Tachinid parasitism rates: DISCUSSION/CONCLUSIONS Prairies tachinid Roadsides did not 12% emerge 17%  No monarch larvae collected in roadsides or prairies were infected with OE during spring 2012, although samples sizes were low. healthy  Tachinid parasitism was higher in roadsides than prairies. healthy 50% tachinid 88% flies  Milkweed density was higher in prairies than roadsides, and highest 33% in the spring.  Asclepias viridis leaves were significantly tougher in prairies than along roadsides. Frequent mowing of roadsides (removing old growth and allowing for the regrowth of tender leaf tissue) is a likely cause. LITERATURE CITED  Additional research is needed to evaluate if mowing could reduce OE ACKNOWLEDGEMENTS 1. Bartel et al. 2010. Monarch butterfly migration and parasite transmission in eastern North infection by removing the above ground portion of plants and America. Ecology 92: 342-351. We thank Grace Ingalls, Kandace Monroe, and Therese Wade for assistance in the field. Funding for 2. Altizer et al. 2000. Associations between host migration and the prevalence of a protozoan reducing the availability of OE spores, or if mowing could increase this project was provided by a Helen Miller Award from the Payne County Audubon Society to parasite in natural populations of adult monarch butterflies. Ecological Entomology 25: 125-139. OE infection by concentrating monarchs in areas where milkweed EKM, a Waters Research Award from the Department of Zoology at Oklahoma State University to 3. Oberhauser et al. 2007. Parasitism of monarch butterflies (Danaus plexippus) by Lespesia EKM, and a USDA-NRI Managed Ecosystems Program grant (2009-35101-05170) to KAB. archippivora (Diptera: ). The American Midland Naturalist 157: 312-328. has regrown.