Catocala whitneyi Dodge, 1874
Basis for Listing
Whitney’s Underwing (Catocala whitneyi) occurs across much of the Great Plains from Manitoba to Oklahoma, extending eastward into the prairie regions of Wisconsin and Illinois with disjunct populations as far southeast as Kentucky and Tennessee (Metzler et al. 2005; Borth and Barina 1991). In Minnesota, it has been documented across the southern half of the state from Chisago, Benton, and Stearns to Big Stone counties and southward, with an outlying northerly record from Itasca State Park (Clearwater, Hubbard, and Becker counties). Additional surveys may extend this range northward. In western Minnesota (Prairie Parkland Province), it appears to be the most common of the leadplant feeding underwings, whereas the Abbreviated Underwing (Catocala abbreviatella) is more prominent in the southeastern counties (Eastern Broadleaf Forest Province).
The moth is restricted to prairie and savanna habitats where leadplant (Amorpha canescens) grows. Like many other prairie specialists, Whitney’s Underwing was probably a common and widespread species across the prairie portions of the state prior to Euro-American settlement, but the widespread destruction of the prairies has left the moth with scattered, often small and ever dwindling habitat patches (Minnesota’s Remaining Native Prairie). Today, the moth can still be locally common in its prairie haunts, but most colonies are highly isolated and thus vulnerable to extirpation by catastrophic events (e.g. drought, fire, pesticides). For these reasons, Whitney’s Underwing was listed as a species of special concern in 2013.
Whitney’s Underwing is a medium-large moth, with a forewing length (base to apex) of approximately 20-23 mm (0.8-0.9 in.). The forewings are medium gray with areas of brownish-gray shading. There are two conspicuous black marks on the forewing. The one closer to the body (submedian line) has some resemblance to a hawkbill knife blade, with the sharp edge facing the wing tip. It begins as a thick bar extending perpendicularly from the wing’s leading edge (costa) from about halfway across the wing and then widens before terminating abruptly in a squared-off end. The other, a variation of the reniform (kidney-shaped) spot commonly present in noctuoid moths, is a right triangle a bit further out the wing, with its hypotenuese parallel to the costa and set back slightly from it. The hind wings (which are concealed at rest) are yellow with two transverse black bands; the marginal band is usually unbroken.
Larvae are pale whitish brown with hues of olive, orange and yellow depending on instar and are marked with longitudinal, semi-irregular grayish-brown stripes and spots (Borth and Barina 1991). The spiracles (breathing pores along each side of the abdomen) are reddish and lack a yellow band below them.
In Minnesota, Whitney’s Underwing is most likely to be confused with the Abbreviated Underwing and Married Underwing (Catocala nuptialis). The Abbreviated Underwing has thinner black forewing markings, and the reniform spot is a dark splotch instead of the black triangle. The Married Underwing forewing has only a faint submedian line, and the reniform spot is solid black and apostrophe shaped. The Married Underwing also flies later in the season (late July-late August), with fresh individuals appearing when Whitney’s Underwing are usually already flight worn.
Whitney’s Underwing occurs in dry to mesic prairies and savanna, where leadplant occurs. Sites in western Minnesota are relatively level to gently hilly mesic to dry prairies, including those with a history of light grazing. The record from Winona County was presumably from a steep, dry and rocky limestone bluff prairie, since it is well documented from this habitat in adjacent Wisconsin. The outlier historical record from Itasca State Park (Laurentian Mixed Forest Province) suggests it may use openings or clearings in dry jack pine (oak) woodlands that support leadplant; it has been documented from this habitat in Wisconsin. Wisconsin sites include additional habitats such as sand prairie and dry oak savanna, which may be utilized in Minnesota as well.
Biology / Life History
Whitney’s Underwing has one generation a year, with adults typically on the wing from early to late July depending on seasonal variation. They are nocturnal but can be flushed with difficulty from prairie vegetation during the day. Adults are best found by means of artificial lights (particularly ultraviolet or mercury vapor) but can also be attracted to bait of rotten banana and brown sugar. Adults apparently visit flowers such as milkweeds (Asclepias spp.) with some regularity as multiple collected specimens from western Minnesota have milkweed pollinia attached to them (Robert Dana, pers. obs.).
Larvae rest near the base of their host leadplant during the day; at night they climb up to the branch tips to feed (Borth and Barina 1991). They are best sought from late May to early June. After this period, larvae form a shelter of silked-together leaves and enter a quiescent prepupal state that lasts for approximately five days. The pupal stage lasts for approximately 2-3 weeks. Adults appear to eclose (emerge from the pupa) only at night.
Conservation / Management
Protection of remaining prairie and savanna habitats with ample leadplant is critical to the survival of the Abbreviated Underwing. This includes habitat management to prevent encroachment by woody vegetation and invasive species. Fire management must be applied with restraint as there is strong evidence from Wisconsin that this moth is fire sensitive. Borth and Barina (1991) failed to find larvae on lush, new leadplant growth following a dormant season burn, whereas larvae were readily detectable in adjacent areas that had not been recently burned. It is, therefore, critical that sites are not burned in their entirety; preferably only a small portion is burned in any one growing season given the risk that this species (as well as countless others) may be localized within a site.
Additional survey work is needed to delineate the range and population status of the Abbreviated Underwing in Minnesota. Research is also needed to assess the effects of various management regimes; how well the moth disperses between habitat patches (to assess the threat of habitat fragmentation), and whether prairie reconstructions can provide suitable habitat.
Several programs and resources are available to land managers and landowners to help protect and manage remaining prairie parcels including the Native Prairie Bank Program, the Native Prairie Tax Exemption Program, and a prairie restoration handbook.
Conservation Efforts in Minnesota
Whitney’s Underwing has only recently been recognized as a species of conservation concern in the state. However, the longstanding efforts to protect remaining native prairie and related habitats by the MN DNR and other public agencies as well as by private conservation organizations, notably The Nature Conservancy, have been of enormous benefit to the moth. Growing recognition of the need to give greater consideration to the effects of prairie management on insects and other arthropods will strengthen the value of habitat protection. Official designation of Whitney’s Underwing as a species of special concern will increase the amount of attention it receives, resulting in greater knowledge of its distribution and abundance in the state. In 2005, the MN DNR began recording field observations of the moth and entering occurrence data into the Natural Heritage Information System.
Kyle Johnson (MNDNR), 2018
(Note: all content ©MNDNR)