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Colias eurytheme Fabricius, 1807
Alfalfa Sulphur; Sulphurs
Family: Pieridae (Whites, Marbles, and Sulphurs)

Species account authors: Crispin Guppy and Jon Shepard.
Extracted from Butterflies of British Columbia.

Introduction to the Lepidoptera of BC

Introduction to the Butterflies of BC
The Families of Lepidoptera of BC

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Distribution of Colias eurytheme in British Columbia.
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Source: Butterflies of British Columbia by Crispin Guppy and Jon Shepard © Royal BC Museum

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Illustration Source: : Butterflies of British Columbia by Crispin Guppy and Jon Shepard © Royal BC Museum

Adult

Orange Sulphurs are very similar to Clouded Sulphurs, but are always predominantly orange on the upperside of males and most females. The black borders of the upperside tend to be broader than in Clouded Sulphurs, and the row of submarginal spots on the underside of the wings are more pronounced. The summer generation has completely orange wings with black borders, and the spring and fall broods have yellow wings with an orange patch restricted to the base of the wings. Most females are orange, or yellow and orange, with black borders. White female Orange Sulphurs have wider black borders, and the spots within the black border are larger, than those of white female Clouded Sulphurs (Hovanitz 1948).

Immature Stages

Eggs are initially white, translucent, and pointed at the upper end; they also have longitudinal ribs. They turn red after a day or two, then black before hatching. Mature larvae have a dark velvety green back, with each segment finely creased. On each side, there is a narrow white lateral line, through the middle of which is a line of vermilion red to orange yellow dashes. The underside is green, and the head is green and translucent. Pupae are light green with a lateral yellow line, above which is a brown point on each segment. A subdorsal brown patch commences at the edge of the wing covers and occupies two or three segments. Another colour form has a whitish lateral line along the abdomen, with a black stripe above the line for the first two or three abdominal segments. Compared with Clouded Sulphurs, the mature larvae of the Orange Sulphur are larger, their lateral spots are a brighter scarlet, and they lack semi-circular black spots under the lateral band. The pupae of Orange Sulphurs have a more attenuated head case, the mesonotal process is less prominent, and some abdominal markings are absent (Edwards 1868-72).

Subspecies

None. The type locality has been restricted to Sacramento, CA (Emmel et al. 1998a).

Colias is the name of a promontory on the coast of Attica where there was a tem pie of Aphrodite. There is no obvious relationship to the butterfly, but the name may be a pun (Emmet 1991). An alternative explanation is suggested under Pontia. The common name "sulphurs" is derived from the yellow "sulphur" colour of most species.

Sulphurs in BC are generally medium-sized butterflies that are yellow, orange, white, or (one species) yellow green with black markings. The wings of males always have a solid black border, with the exception of the Arctic Sulphur. The black borders of females contain extensive pale areas, or may be greatly reduced or absent. There are several multivoltine species that show considerable seasonal variation in wing colour.

There are about 70 species of Colias in the world. The centre of distribution in North America is BC, with more species (13) than any other province or state. Colias species may all be inter-fertile, with natural hybrids known for most species combinations where they occur together in the wild. The species have behavioural, ecological, and physiological differences that maintain separation of the species in the wild (Hovanitz 1963).

Eggs are laid singly on the leaves of the foodplants, and are pale yellow green to cream, later turning orange. Young larvae are slender, yellowish or green, and smooth-skinned with a thin coat of fine hairs. Mature larvae are yellow green or green with fine black dots all over, and stripes of various colours running along the back and sides. Sulphurs hibernate as second to fourth instar larvae (except Canadian Sulphurs, which hibernate as fifth instar larvae), and then complete development in the spring. There are five larval instars in all Colias (Ae 1958a). Pupae are fastened head up with a girdle around the middle.

Members of the genus utilize a wide range of foodplants, although each species specializes to a greater or lesser extent. Larvae of sulphurs feed on plants in three groups: legumes (Fabaceae), Vaccinium (Ericaceae), and Salix (Salicaceae). Sulphurs occur in a wide range of habitats, including arid sagebrush areas, alfalfa fields, meadows, alpine tundra, and forest bogs.

Sulphurs always rest with their wings folded over their backs, and bask in the sun by leaning to the side to allow the sun to warm the underside of their wings. It has been demonstrated for several species (C. meadii, C. nastes, C. philodice, and C. eurytheme) that the darker the pigmentation on the underside of the wings, the more heat can be absorbed from the sun while basking, permitting greater flight activity in cold environments (Kingsolver 1985).

There is relatively little variation in wing pattern between many species, making identification difficult. The key characters mentioned in the species discussions are shown in the figure.

Orange Sulphurs are on the wing from April to October, with at least three broods. In BC they are seldom seen before midsummer, when they migrate into the province. Orange Sulphur larvae do not go into hibernation in the fall, unlike those of Clouded Sulphurs (Ae 1958a), so they cannot survive through the winter in BC. Hybridization with Clouded Sulphurs is minimized because females normally mate only with males that have ultraviolet reflective wings and the correct male pheromone. Females start laying eggs when they are several days old, and in captivity lay an average of 700 eggs in their lifetime. Eggs are laid singly on leaves, and young larvae eat holes in the top of the leaves. Older larvae feed on the tip of the leaves, and the largest larvae eat each half of the leaf separately. If the weather is too hot, resulting in larval body temperatures over 32°C, or too cold (body temperature below 15°C), the larger larvae move to the base of the larval foodplant (Sherman and Watt 1973). Orange Sulphurs can be a crop pest on alfalfa in warm areas of the southern USA (Allen and Smith 1958), but in the cool climate of BC their populations never get large enough to be a serious problem.

Orange Sulphurs commonly use alfalfa as a larval foodplant in BC, and it appears to be the preferred foodplant. Outside BC other foodplants include red clover, white clover, Astragalus flexuosus, A. agrestis, A. bisulcatus, A. whitneyi, A. drummondii, Lupinus argenteus, Medicago lupulina, Melilotus officinalis, Trifolium fragiferum, T. hybridum, T. longipes, T. nanum, T. wormskholdii, Vicia americana, and V. sativa (Emmel and Emmel 1962; Emmel et al. 1971; Shapiro and Shapiro 1974; Shapiro 1975b; Scott 1992).

BC is at the northern edge of the range of Orange Sulphurs. They migrate north from WA, ID, and MT in the late summer, resulting in their widespread occurrence across southern BC in warm summers. They rarely occur north of the Thompson River valley. Orange Sulphurs are sometimes encountered in subalpine and alpine areas during migratory flights, but they primarily inhabit low-elevation alfalfa fields and nearby natural or weedy habitats containing naturalized alfalfa.

Distribution

Orange Sulphurs occur from BC to NF as breeding migrants, and south throughout the USA and MEX, from coast to coast. Migrants extend north to NT, east of the Rockies.

Origin Status	Provincial Status	BC List (Red Blue List)	COSEWIC
Native	S5B	Yellow	Not Listed

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