Montana Field Guide

[From Ferris and Brown 1981; Scott 1986; Opler and Wright 1999; Glassberg 2001; Pyle 2002] Forewing 2.0-2.8 cm. Uppersurface base color white, male with black checkered pattern on outer half of forewing and black cell mark, white on hindwing; female more heavily checkered, markings more brown and diffuse, including hindwing. Undersurface may be yellow-veined with brown or olive submarginal chevrons, male faintly checkered on hindwing, female with yellow-tan markings on hindwing and forewing apex; both sexes with black cell mark present. Spring and fall ("short-day") form with hindwing veins on the undersurface outlined in gray-green.

Many flights, early spring through fall (Scott 1986). Mainly February to November, except mostly July and August in Canada and Pacific Northwest (Glassberg 2001). Early spring to late fall in the Rocky Mountain states (Ferris and Brown 1981), early April to late October in Colorado (Scott and Scott 1978), early June to late September in Oregon and Washington (Pyle 2002), late May to early October in Oregon (Warren 2005), mid-summer to late fall in British Columbia and Alberta (Guppy and Shepard 2001).

Best determined by a combination of white uppersurface more or less marked with black, charcoal, or brown checks, bars, chevrons; undersurface of hindwing and forewing apex may be with yellow vein markings with brown or olive submarginal chevrons. Paler, thinner markings along veins, and habitat, also useful for separating similar-appearing species.

Partly migratory; resident in the western US in the south (southern California, Arizona, New Mexico, Texas), occurring only as non-overwintering immigrants farther north in the range, including the Pacific Northwest and Montana (Scott 1986; Guppy and Shepard 2001; James and Nunnallee 2011).

Open areas, montane meadows, agricultural fields, weedy fields, arid lands, desert, prairie, suburbs, disturbed sites (Ferris and Brown 1981; Scott 1986; Opler and Wright 1999; Glassberg 2001). In Glacier National Park, Montana reported from montane mesic meadows and above treeline in alpine terrain (Debinski 1993); in the Greater Yellowstone Ecosystem, reported from fields, roadsides, vacant lots, cultivated lands, disturbed areas (Debinski and Pritchard 2002).

Larval food plants primarily introduced and native mustards, including Arabis, Barbarea, Berteroa, Brassica (several species), Cakile, Capsella, Cardaria, Caulanthus, Chorispora, Descurainia, Hersperis, Hirschfeldia, Lepidium (several species), Lobularia, Malcolmia, Physaria, Raphanus, Rorippa, Schoenocrambe, Selenia, Sinapis, Sisymbrium, Thelypodium, and Thlaspi, as well as some non-mustard taxa, including Cleome, Nasturtium, Reseda, and Wislizenia (Emmel et al. 1970; Scott 1986, 1992, 2006; Graves and Shapiro 2003). Adults feed on flower nectar (including Abronia, Achillea, Allium, Ammannia, Apocynum, Arctium, Arnica, Asclepias, Astragalus, Berteroa, Bidens, Blephilia, Boltonia, Campanula, Centaurea, Chorispora, Chrysanthemum, Chrysothamnus, Cirsium, Cleome, Convolvulus, Coreopsis, Cosmos, Cryptantha, Delphinium, Descurainia, Dipsacus, Echimacea, Epilobium, Erigenia, Erigeron, Eriogonum, Eryngium, Erysimum, Eupatorium, Euryops, Grindelia, Helianthus, Hesperis, Heterotheca, Hymenopappus, Lavandula, Lepidium, Limonium, Linum, Lobelia, Lygodesmia, Machaeranthera, Medicago, Melephora, Melilotus, Myosotis, Nepeta, Orbexilum, Oxalis, Potentilla, Prunella, Psoralea, Pycnanthemum, Rudbeckia, Salvia, Sedum, Senecio, Solidago, Sphaeralcea, Spiraea, Symphyotrichum, Tagetes, Taraxacum, Thelesperma, Tribulus, Verbena, Verbesina, Veronica, Zinnia) and mud (Tooker et al. 2002; Scott 2014).

Females lay eggs singly (50 eggs reported for one captive female) on host plant infloresences, flower buds, tops and bottoms of leaves, stems; live about 7 days as adults in the wild (Scott 1986, 1992, 2006; James and Nunnallee 2011). Eggs per ovariole (1/8 total number) about 140 (Ehrlich and Ehrlich 1978). Eggs hatch in about 3 days post egg-laying (depending on temperature), develop to L5 instar and pupate in about 15-16 days, adults eclose (emerge from pupae) in about 10 days, males emerging a few days before females (James and Nunnallee 2011). Larvae solitary, prefer to feed on flower buds, flowers, fruits, but feed on all parts of host plants, build no nest, overwinter as pupae (Scott 1979, 1986, 1992; James and Nunnallee 2011). Males patrol hilltops and flats near host plants in search of females (Scott 1975b, 1986).