Basis for Listing
The persius duskywing, also known as the hairy duskywing, comprises an eastern subspecies Erynnis persius persius, and one or more western subspecies. The eastern subspecies is limited to a narrow zone from Maine and Virginia westward through the Great Lakes to southeastern Minnesota. The species is widely distributed in western North America, from Manitoba and the western Dakotas south to New Mexico and west to Alaska and California (Layberry et al. 1998; Opler et al. 2006). Layberry et al. (1998) assign all these western populations to a single subspecies, E. persius borealis. The eastern subspecies occurs in open, sandy savannas and barrens where its larval host plants, primarily wild blue lupine (Lupinus perennis) but sometimes also yellow wild indigo (Baptisia tinctoria), are common. The eastern subspecies of the persius duskywing is now rare throughout its range primarily because of destruction of the specialized habitat of its larval host plants (NatureServe 2008). This is the same habitat required by the federally threatened Karner blue (Lycaeides melissa samuelis), which is also the eastern subspecies of a species widely distributed in western North America.
The persius duskywing has only been recorded from a single site in southeastern Minnesota, in Winona County. Observations to date indicate that this colony is very small (Cuthrell 1990; R. Huber, pers. comm.). A Minnesota DNR survey of all known sites in Minnesota having suitable habitat did not find this species elsewhere (Cuthrell 1990), nor have other experienced lepidopterists who have visited these sites. Given its extreme rarity in the state, the persius duskywing was listed as an endangered species in Minnesota in 1996.
The persius duskywing is one of several very similar looking skippers that occur in Minnesota. Like the other duskywings, it is a small butterfly (forewing length 1.1-1.5 cm (0.43-0.59 in.) from base to apex), with rounded wings, a moderately robust body, and antennae that end in a slender, curved or hooked club. It is dark blackish brown above, slightly lighter below. Males have a very subtle gray mottling on the forewings above, which is more pronounced in females. There is a short row of very small translucent spots forming a line perpendicular to the leading edge of the forewing out near the tip in both sexes. Females usually have a few additional, larger spots in the more central part of the wing, but these are reduced or absent in males. These skippers frequently alight on the ground where they hold their wings spread flat or even pressed against the surface.
The persius duskywing resembles several other duskywing species in Minnesota. The dreamy duskywing (Erynnis icelus) is smaller and the upper surface of the forewings is much more strongly mottled. There are no translucent spots. The sleepy duskywing (E. brizo) is browner and lacks the gray dusting on the upper forewings. It also lacks translucent spots. Juvenal's duskywing (E. juvenalis) is larger than the persius, and the translucent spots on the forewing are usually prominent. Juvenal's also has two conspicuous light spots near the apex of the hind wing beneath. Both sexes of the mottled duskywing (E. martialis) have a very mottled appearance on both hind and forewings above, and fresh individuals have a purplish sheen. Distinguishing the persius duskywing from the wild indigo duskywing (E. baptisiae) and the columbine duskywing (E. lucilius) is especially difficult, and records without voucher specimens are unreliable. In the persius duskywing, the inner margins of the little spots near the apex of the foreweing form a nearly straight line whereas they are more irregularly arranged in the other two species. The persius duskywing also has long, white or gray hairlike scales that stand above the flat scales on the upper forewings. These wear off and reliable determination of worn specimens requires examination of genitalic characters. Two other similar-looking skippers are the northern cloudywing (Thorybes pylades) and southern cloudywing (T. bathyllus). These lack the long hairlike scales on the forewings, have very little grayish mottling of the forewings above, and have a number of translucent white spots on the forewings, usually quite large in the southern cloudywing. The hind wing below has a distinct banded pattern, not the light flecks the persius duskywing has. They also tend to hold their wings at a more erect angle when resting or feeding.
Minnesota's only occurrence of the persius duskywing is in a mosaic of oak woodland and savanna or barrens on sand where wild blue lupine is common. This is similar to the habitat reported for Wisconsin and Michigan occurrences (Swengel and Swengel 1997; Nielsen 1999).
Biology / Life History
The persius duskywing has a single annual generation. The adult flight period is in May and early June in Minnesota. In Michigan, the mature larva hibernates and pupates in early spring (Nielsen 1999).
Scudder (1864) reported willow (Salix spp.) and poplar (Populus spp.) to be larval host plants in his original description of this species, but all recent work strongly indicates that wild blue lupine is the principal larval host, with yellow wild indigo (possibly other wild indigo species) being used in some locations. Larval hosts for the western population are all members of the pea family (Fabaceae) (Scott 1986). Larvae share the habit of other members of the same genus of tying leaves of the host plant together with silk to form a simple shelter in which they rest between bouts of feeding. Adults have been observed taking nectar from a variety of plants (Nielsen 1999), suggesting that they will visit any available flowers.
Males seek receptive females primarily by perching on low vegetation or bare spots and pursuing any passing insect that might be a female persius duskywing. The courtship and mating behavior of the eastern subspecies does not appear to have been described. Nothing is known about the dispersal behavior of mated females.
Conservation / Management
The small size of Minnesota's only known colony is the primary threat facing the persius duskywing in the state. Such a small, isolated colony is at high risk of extirpation resulting from both natural events (such as severe drought or hailstorms) and human caused ones (such as insecticide application), as well as from the vagaries of normal population processes (for example, by chance all adults in one generation are males). Loss of genetic diversity in a small population is another possible threat. The Minnesota colony is at least 80 km (48 mi.) from the nearest known occurrences in Wisconsin (Eau Claire and Jackson counties), making it unlikely that immigration from the Wisconsin population will maintain genetic diversity.
The possible fragmentation of this small colony into even smaller units confined to the separate patches of suitable habitat aggravates the risk of extirpation. Fire suppression has allowed the original oak scrub and woodland matrix to grow up into dense woodland and forest that probably impedes butterfly movement among the patches, and even these have been shrinking as oaks invade. The persius duskywing is probably highly susceptible to fire as larvae are in the lupine foliage. Prescribed burn units should be configured to always allow for butterfly survival in unburned parts of each habitat patch, and rotation should allow for population recovery between burns (this would be longer than for the Karner blue because the Karner blue has two generations per season). An intensive survey to determine the distribution of the persius duskywing among the habitat patches and its abundance is needed to design an appropriate fire management regime. Mechanical clearing is an option where fire would be risky, but the long-term suitability of areas managed exclusively with mechanical clearing is unknown. Opening up woodland and forest between patches to provide greater connectivity can be done at little or no risk to the butterflies.
The gypsy moth (Lymantria dispar) will soon invade the area where the persius duskywing occurs. The oak-dominated woodlands and forests here are prime candidates for defoliating outbreaks, and there will be considerable pressure to control gypsy moth numbers with insecticides. Two products used for this purpose are diflubenzuron (Dimilin) and the toxin derived from the bacterium Bacillus thuringiensis var. kurstaki (Btk). Both are likely to be highly toxic to the persius duskywing, and it will be imperative to keep application of either of these products well away from any habitat where this species occurs.
Conservation Efforts in Minnesota
All of the known habitat occupied by the persius duskywing in Minnesota is within a Wildlife Management Area owned by the Minnesota DNR. Because this area is also critical habitat for the Karner blue, there is an ongoing research and management effort on behalf of that butterfly which should be equally beneficial for the persius duskywing. The need for additional information about the distribution and abundance of the persius duskywing within the site has already been noted.
There are few known occurrences in Minnesota of habitat suitable for the persius dusk wing. These areas were surveyed for the Karner blue in 1990 by the Minnesota DNR (Cuthrell 1990), and the persius duskywing was also included as a target species by the surveyor. The persius duskywing was only found at the one known location. The other sites have also been visited one or more times by other experienced lepidopterists with the same results.