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Montana Field Guides

Western Sulphur - Colias occidentalis


Global Rank: G4
State Rank: SNR

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General Description
Several authorities do not include Montana in the range of this species (Scott 1986; Ferris 1993; Glassberg 2001; Guppy and Shepard 2001; Pyle 2002; Warren 2005). The confusion seems to center on whether or not to treat the christina form as a full species (see Christina Sulphur, C. christina, account) or as a subspecies of C. occidentalis (Hammond and McCorkle 2003; Scott et al. 2006). Scott et al. (2006) refer to the C. alexandra-occidentalis complex (part of the legume-feeding species) as a "stenchospecies" for taxa that "will stink up every person studying them even if he does a thorough 'ideal' study" (Scott et al 2006:1). Given the taxonomic uncertainty and instability, this account probably includes information pertaining to more than one species.

[From Ferris and Brown 1981; Scott 1986; Ferris 1993; Opler and Wright 1999; Glassberg 2001; Scott et al. 2006] Forewing 2.4-2.9 cm. Fringes pink; wing coloration variable. Uppersurface yellow (to whiteish in females) with black scaling at wing base, male with narrow black border border; female with reduced or absent black border; with small black forewing cell spot, pale to bright orange hindwing discal cell spot. Undersurface of forewing yellow; hindwing yellow to golden, with evenly scattered dusting of black scales, a dark smudge near leading margin, cell spot large, pearly, round, rimmed with dark red, often with small satellite above, no marginal markings.

Phenology
One flight, late May through June (Scott 1986). May to September (Glassberg 2001). Early May to late September in Oregon and Washington (Pyle 2002; Warren 2005), June to September in British Columbia (Guppy and Shepard 2001).

Diagnostic Characteristics
Best determined by a combination of undersurface of hindwing yellow to golden, with evenly scattered dusting of black scales, a dark smudge near leading margin, cell spot large, pearly, round, rimmed with dark red, often with small satellite above, no marginal markings.

Species Range
Montana Range

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Range Comments
Southern British Columbia south to central California, east to western Idaho, northeastern Oregon, disjunct population in northern Utah (Scott 1986; Ferris 1993; Glassberg 2001; Guppy and Shepard 2001; Pyle 2002); other authorities include southwestern Alberta, western Montana, northwestern Wyoming (Opler and Wright 1999; Scott 2006); 610 m to at least 1829 m elevation in Oregon (Warren 2005), sea level to treeline in Washington (Pyle 2002) and British Columbia (Guppy and Shepard 2001). In Montana, depending on authority, either entirely absent or reported from at least 13 counties in the western 1/3 of the state (Kohler 1980; Stanford and Opler 1993; Scott et al. 2006). Locally uncommon to common (Glasberg 2001).

Migration
Non-migratory.

Habitat
Open areas, including open pine and Douglas-fir forest, montane meadows, roadsides, powerline corridors, to treeline (Scott 1986; Ferris 1993; Opler and Wright 1999; Glassberg 2001; Guppy and Shepard 2001; Pyle 2002; Warren 2005; James and Nunnallee 2011). In Glacier National Park, Montana reported from xeric montane meadows and above treeline in alpine terrain (Debinski 1993), but this may pertain to C. christina depending on taxonomy.

Food Habits
Larval food plants include native and exotic Lathyrus (multiple species), Lupinus (multiple species), Melilotus, and Vicea (multiple species) (Scott 1986; Ferris 1993; Graves and Shapiro 2003; Warren 2005; James and Nunnallee 2011), possibly Lotus (Scott 1992). Adults feed on flower nectar (including Apocynum, Asclepias, Brodiaea, Calochortus, Cirsium, Lilium, Taraxacum) and mud (Pyle 2002; James and Nunnallee 2011; Scott 2014).

Reproductive Characteristics
Limited information, given the taxonomic confusion of the species complex. Females lay eggs singly on the upper surface of host plant leaves (Scott 1986; James and Nunnallee 2011). Eggs hatch in about 6-7 days (depending on temperature), reach L3 instar in about 17-20 days post egg-hatch then hibernate (enter diapause), develop further to L5 instar and pupate in about 20 days after exiting diapause in spring (depending on temperature); adults eclose (emerge from pupae) in about 7 weeks (James and Nunnallee 2011). Larvae eat host plant leaves, build no nests, overwinter as L3 instar in folded leaf (Pyle 2002; James and Nunnallee 2011). Males patrol throughout the day in valley bottoms, hillsides, open woods, meadow edges, streamsides, in search of females (Scott 1975b, 1986; James and Nunnallee 2011).

References
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Citation for data on this website:
Western Sulphur — Colias occidentalis.  Montana Field Guide.  .  Retrieved on , from