Figs 7, 8, 138, 196. Map 2
Plusia secedens Walker, [1858]: 913.
Anarta secedens; Smith 1893a: 294.
Polia secedens; McDunnough 1938: 70.
Anartomima secedens; Franclemont and Todd 1982: 149.
Lasionycta secedens; Hacker et al. 2002: 152.
Anarta bohemani Staudinger, 1861: 370.
Anartomima bohemani; Boursin 1952: 55.
Anartomima secedens bohemani; Kononenko et al. 1989: 553.
Lasionycta secedens syn. bohemani; Hacker et al. 2002: 149.
Type material. Plusia secedens: holotype ♁ [ BMNH, examined]. Type locality: St. Martin’s Falls, Albany River, Hudson Bay, [ Ontario, Canada]. Anarta bohemani: holotype ♁ [ ZMHB, not examined]. Type locality: Lapland.
Diagnosis. Lasionycta secedens is easily identified without dissection by the combination of dark-gray to black-gray forewing and vivid yellow hindwing with black along the costal and distal margins. Lasionycta leucocycla albertensis (McDunnough) and L. illima sp. n. that also have yellowish hindwings lack black on the costa. Lasionycta secedens is the only Lasionycta in which the male lacks a postsaccular flap and the female has a strongly spiraled appendix bursae.
Distribution and biology. Lasionycta secedens is Holarctic. North American populations are distributed from Labrador, northern Manitoba, and Alaska southward to northern Maine, northern Minnesota, and south-central British Columbia. It is found in boreal forest, especially bogs, and is both diurnal and nocturnal.
Ahola and Silvonen (2008) report that early instar larvae prefer to feed on the epidermis of leaves of Vaccinium vitis-idaea L. ( Ericaceae), but is polyphagous when reared. In Scandinavia the larva overwinters twice. In Minnesota this species occurs in raised bogs with V. vitis-idaea (K. Johnson pers. comm.) suggesting that this is the foodplant in North America.
Geographical variation. Populations of L. secedens are arranged in two subspecies.