The Diana fritillary, Speyeria diana (Cramer 1775) (Nymphalidae), is considered a rare species across most of its range (Rudolph et al. 2006; Campbell et al. 2007). The North Carolina and Arkansas Heritage Programs currently list S. diana as an imperiled species of special concern (rank S2/S3) due to its rapid decline over the past two decades; it is also included on the Xerces Society Red List of Pollinator Insects (Vaughan & Shepard 2005; Howard & Legrand 2009). The conservation network, NatureServe, assigns S. diana a Global Status of G3/G4, which describes the species as very rare or local throughout its range, found locally in a restricted range (21 to 100 occurrences), and threatened throughout its range (NatureServe 2008). Because of its rapid disappearance across portions of its former distribution, S. diana may soon become a candidate for listing under the Endangered Species Act of the United States (Federal Register 1991, Vol.56, no. 225, pp. 58, 831). Currently, S. diana is not protected through any special conservation status, although it appears to be declining across certain portions of its distribution (Carlton & Nobles 1996; Moran & Baldridge 2002; Cech & Tudor 2005; Wells unpublished).
Our goal here is to describe the reproductive behavior of S. diana observed during two separate occasions in Mount Magazine State Park, Arkansas, in the summer of 2007. We are aware of only two published accounts of this species mating in the wild, one from Missouri in 1853 (Strecker 1900), and the other more recently from Bath County, Virginia (Cohen & Cohen 1991).
Bionomics. The Diana fritillary is univoltine, producing one generation per year. Adult males emerge and take flight in late May, typically several weeks before females (Allen 1997; Cech & Tudor 2005). Males patrol along the edge of forest habitat, and have an active and mobile lifestyle. While males begin to die off in late July, females persist somewhat cryptically into early October (Opler & Krizek 1984; Adams & Finkelstein 2006). Females are believed to be longer lived than the males, and are often found resting quietly in the cover of forest for much of the day, nectaring or ovipositing on the forest floor (Klots 1951; Spencer 2006).
In general, S. diana inhabits moist cove forests and deep woodland areas near streams. Adult Diana fritillaries are often found in open areas feeding on tall, high-quality nectar sources such as milkweeds, butterfly bushes or large fall composites (Moran & Baldridge 2002; Spencer 2006; Ballosser 2007; Ross 2008). Violets (Viola, Violaceae) are the only larval host plants used by Speyeria. Each female Diana fritillary can lay thousands of eggs singly on ground litter during the month of September in the vicinity of violets (Allen 1997; Cech & Tudor 2005). The hatched larvae immediately burrow deep into the leaf litter of the forest floor where they overwinter until the following spring.
Historical observations. According to natural historical accounts, the orange and black S. diana male was first noted when the type specimen of this species was initially described by the Dutch naturalist Pieter Cramer near Jamestown, Virginia (Cramer & Stoll 1777; Klots 1951). These coastal populations of S. diana have since been extirpated since the 1950s (Scott 1986; Howard & Legrand 2009). In August 1864, the prominent 19th century lepidopterist, William Henry Edwards, was the first to formally describe natural populations of the iridescent blue-green female S. diana, then Argynnis diana, in Kanawha, West Virginia (Edwards 1864). Holland (1883) captured and pinned what he believed at the time to be the “first specimen of the female Argynnis diana ever put upon an insect pin” sometime between 1858 and 1861 in Salem, North Carolina. However, a note published by the renowned entomologist, Herman Strecker, dated 9 March 1900 describes what is likely the actual earliest described female S. diana held in the collection of a Baltimore collector and lepidopterist, J.P. Wild. In this note, Strecker described what was defined taxonomically at that time as a female of Argynnis diana captured in copula with a male in Missouri around 1853 (Strecker 1900). Upon inspection of the Strecker collection, most of which is now held at the Field Museum of Natural History in Chicago, Illinois; however, we were not able to find any copulating pair of Diana fritillaries. In fact, we found no S. diana specimens from Missouri in the entire Strecker collection. We welcome any knowledge of the whereabouts of the afore mentioned Strecker specimens, as well as any other historical accounts of mating in S diana.
Field observations. We observed two copulating pairs of Diana fritillaries on 9 and 23 June 2007 in Mount Magazine State Park, Logan County, Arkansas (Fig. 1). Mount Magazine State Park is one of Arkansas' newest state parks, and is managed by Arkansas State Parks through a special partnership with the US Forest Service. The Park conserves 904 hectares of mountain habitat, including Arkansas' highest point at 840m, and is surrounded by more than 4,500 hectares of mixed, moist deciduous forest in Ozark National Forest. The US Forest Service designates 14 invertebrate species found in Mount Magazine as endemic, rare, sensitive or threatened, including S. diana (Ross 1998).
We observed S. diana copulation for a duration of 4hrs on 9 June 2007, and for 2hrs on 23 June 2007, between 1200 hrs and 1700hrs. In general, nymphalids are known to mate for durations of thirty minutes to over 5hrs (Brower et al. 1965; Miller & Clench 1968; Pliske & Eisner 1969). We observed dozens pairs of S. cybele mating in the same vicinity, and at the same time, as S. diana. The mating behaviors of S. diana appear to be highly similar to that of the widespread great spangled fritillary, S. cybele, lending observational support to hypotheses relating S. diana and S. cybele as probable sister species (Hammond 1978; Baltosser 2007; Dunsford 2009).
We witnessed carrying pair behavior in S. diana during copulation, which is rarely observed in nature. During both of our observations, the female Diana fritillary alighted, carrying the limp male high into the branches of the forest after several hours of copulation. The only other published description we have found of S. diana mating behavior was Cohen & Cohen (1991), who also reported the S. diana female carrying the male in Bath County, Virginia. The carrying pair behavior we observed in S. diana is consistent with that displayed by other butterflies in the genus Speyeria, where females frequently carry their male partners during mating (Shields & Emmel 1973).
The habitats where we encountered mating pairs of S. diana and S. cybele were open fields that contained a rich mix of high quality nectar plants bordered by dense forest. We noted the following plant species present where S. diana and S. cybele pairs were mating: coreopsis (Coreopsis lanceolata), purple coneflower (Echinacea purpurea), butterfly weed (Asclepias tuberosa), bee balm (Monarda spp.), yarrow (Achillea millefolium), ironweed (Vernonia spp.), thistle (Cirsium spp.), and goldenrod (Solidago spp.). During both of our observations, the female S. diana nectared on purple cone flower throughout copulation (Fig. 1), while the males did not ever feed. It has previously been suggested that Speyeria butterflies may confine their activities to particular types of nectar-producing flowers, specifically those that provide the highest quality of energy-packed sugars (Ross 2003; Rudolph et al. 2006). Future investigation that quantifies nectar quality across a wide variety of S. diana habitats would be very useful in examining relationships between S. diana reproductive behavior and floral composition.
While our field observations are limited in scope, they provide important insight into the copulation, mating time, and carrying pair behavior of a threatened North American butterfly that is rarely seen mating in nature. Future investigation should focus on quantifying specific habitat requirements for S. diana, including the documentation of larval and nectar plant associations across this species' entire distribution to better inform future conservation efforts.
We would like to thank our colleagues for ongoing discussion on this topic, including Dr. William Baltosser (University of Arkansas, Little Rock, AR), and Eric Smith (Caldwell Community College and Technical Institute, Boone, NC). We are grateful to Dr. Peter Adler and the anonymous reviewers who offered helpful comments that improved this note.