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Lepidoptera. Peter J. Herlan of the Nevada State Museum and his wife Barbara assisted greatly during field work in Nevada. Oakley Shields and Scott Ellis assisted in field collection of material.
Literature Cited
Comstock, J. A. 1928. Early stages of Papilio pergamus. Bull. So. Calif. Acad.
Sci. 27: 82-86. ---------- & L. M. Martin. 1955. A new Papilio from California. Bull. So. Calif.
Acad. Sci. 54: 142-150. Emmel, J. F. & T. C. Emmel. 1964. The life history of Papilio indra minori. J.
Lepid. Soc. 18: 65-73. ----------. 1966. A new Papilio from the Mojave Desert of California (Lepidoptera:
Papilionidae). Entomol. News 77: 57-63. ----------. 1968. The population biology and life history of Papilio indra martini.
J. Lepid. Soc. 22: 46-52. Emmel, T. C. & J. F. Emmel. 1967. The biology of Papilio indra kaibabensis
in the Grand Canyon. J. Lepid. Soc. 21: 41-48. ----------. 1971. A new subspecies of Papilio indra from central Nevada (Lepidoptera:
Papilionidae). Pan-Pacific Entomol. 47: 220-223. ----------. 1973. The Butterflies of Southern California. Los Angeles Co. Mus. Nat.
Hist., and Ward Ritchie Press, Los Angeles.
FIELD OBSERVATIONS ON COLIAS ALEXANDRA EDWARDS
(PIERIDAE)
Scott L. Ellis
1217 4% St. N.W., Rochester, Minnesota 55901
In recent years there has been vigorous interest in all aspects of the biology of North American species of Colias. Colias alexandra Edwards, a widespread species of the western foothills and mountains has attracted increased attention. Hovanitz (1950a) described its distribution, and (1950b) plotted frequencies of the dimorphic females. Ae (1959) induced laboratory crosses between C. alexandra and C. euryiheme Bois-duval. Masters (1970) and Ferris (1972, 1973) examined the taxonomy of the species. John M. Burns (unpubl.) has studied the electrophoretic variation of esterase in different Colias species, including alexandra. An attempt is made here to augment this work with notes on foodplants, population structure, and behavior in Colias alexandra. Observations were made on 35 C. alexandra populations during 1971 and 1972 in Colorado, Utah, Nevada, Idaho, and Montana.
Colias alexandra is widely distributed along the axis of the Rocky
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Mountains from New Mexico to Alberta and British Columbia, with outlying populations to the west in the Great Basin areas of Utah, Nevada, Idaho, eastern California, and then northward into eastern Oregon and Washington. East of the Rockies isolated populations occur in western Nebraska and the Black Hills of South Dakota. If christina Edwards is accepted as a subspecies of alexandra, the range is extended northeastward from Montana to Manitoba and northward to the Yukon River to approximately 67°N. For a distribution map and current taxonomic treatment, see Ferris (1973). C. alexandra is found in dry, open associations of the Transition and Canadian zones, most frequently from 7500-9000 ft. in the Colorado Rockies to 2000 ft. in northern Idaho.
Oviposition Records. Edwards (1897) lists Thermopsis (Leguminosae) and Astragalus (Leguminosae) as natural foodplants. He found clover Trifolium repens L. (Leguminosae) to be a satisfactory laboratory host. Edwards received alexandra ova from several workers in Colorado. Edwards noted in his entomological journals that he received alexandra ova on 27 July 1884 laid on Astragalus from Nash at Rosita, Wet Mtns., Custer Co., Colorado. He also received eggs from Prof. G. H. French at Central City, Gilpin Co., laid 27 July 1886 on Thermopsis. Edwards (1873) reports that Mead observed alexandra ovipositing on Lupinus (Leguminosae) in the northern part of South Park, probably in present-day Park Co., Colorado. From my experience with alexandra over much of its range, it appears that members of Lupinus are unlikely foodplants. Mead had only limited experience with the Colorado flora at the time of his observation, and may have misidentified the foodplant. McDunnough (1922) notes an oviposition by Colias christina in Alberta on a "small species of lupine with a greenish-white flower." This vague description might apply to Astragalus canadensis L. var. mortonii (Nutt.) S. Watson, a foodplant for alexandra in northern Idaho and western Montana. Klots, in Ehrlich & Ehrlich (1961), lists Astragalus and Medicago as foodplants. Shields & Emmel (1969) observed oviposition on Astragalus miser Dougl. in the Wasatch Range in Sanpete Co., Utah. Ferris (1973) cites Astragalus serotinus as a foodplant. Barneby (1964) considers serotinus (Gray) a variety of Astragalus miser.
Unpublished oviposition records unsubstantiated by herbarium determinations include Thermopsis pinetorum Greene from the White Mountains, Arizona, by Kilian Roever; Thermopsis divaricarpa A. Nels., Rampart Range Road, NE of Woodland Park, Teller Co., Colo., by F. M. Brown (photograph of ovum on plant). No ovipositions have yet been observed on Thermopsis montana Nutt., a species widespread west of the continental divide in Colorado. Kearney & Peebles (1951) consider T. pinetorum "doubtfully distinct" from T. montana. Mike Fisher ob-
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served oviposition on Oxytropis lambertii Pursh. (Leguminosae) near Parker, Douglas Co., Colorado.
Foodplant-butterfly Relationships. Repeated ovipositions on a plant species in one locality, or oviposition on the same plant species in different localities is considered here to be a strong confirmation that the oviposition plant is the foodplant. No obvious oviposition mistakes were seen. Astragalus eremiticus is the only foodplant listed for which there is only a single oviposition sighting.
Many members of the genus Astragalus and Oxytropis are known to accumulate toxic compounds in their systems, especially the element selenium. Colias alexandra oviposited on Astragalus miser, A. bisulcatus, and Oxytropis lambertii, which are frequently poisonous to livestock. The toxicity of A. miser appears to vary as a function of the selenium concentration of the many different types of soil the plant inhabits. Barneby (1964) notes that "miser var. oblongifolius is often browsed, even where innocuous feed is plentiful, at least in the Colorado Rocky Mountains." For A. bisulcatus, Barneby (1964) states that: "On warm days and while drying in the press, the herbage gives out a strong smell of selenium disagreeable to most people and to some actually nauseating. It is one of the most dangerous and widely dispersed of the seleniferous stock poisons." A study of the biochemical relationship between C. alexandra and A. bisulcatus might prove rewarding, particularly if selenium is metabolized and stored in the immature and adult stages of the butterfly.
The ranges of C. alexandra foodplants often greatly exceed the range of the butterfly. Of particular interest is the absence of alexandra in most parts of Arizona, especially on the Kaibab Plateau north of the Grand Canyon (Kilian Roever, pers. comm.) where varieties of A. lentiginosus, A. miser, and A. bisulcatus are known to occur. C. alexandra is known from the nearby mountains in southwestern Utah. Astragalus canadensis has one of the widest ranges of any North American Astragalus, embracing nearly the entire eastern half of the United States, ranging south to the coast of Texas. A. lentiginosus is a highly polymorphic species that lives in a great range of environments and altitudes, and includes several varieties that occur in the deserts of southern Arizona and California. It is possible that C. alexandra has a physiological intolerance to the higher temperatures of desert areas, although a population at 5600 ft. in the arid Henry Mountains of southern Utah indicates that alexandra should be sought in comparable environments in northern Arizona. Much of eastern Colorado, Wyoming, South Dakota, eastern Montana, and Alberta remain for further foodplant investigations.
Many members of the genus Astragalus are pioneer or "fugitive" spe-
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cies, often colonizing barren ground unacceptable to other plant species, and then disappearing as more competitive species enter the area (Barneby, 1964). Several parallel cases of local abundance of a C. alexandra foodplant appeared to be the result of disturbance of the plant community by man and his animals. In the La Sal Mountains of Montrose Co., Colorado, large stands of Lathyrus leucanthus were found growing next to stumps of Pinus ponderosa Lawson cut within the previous two years. In Piute and Juab Counties, Utah, Astragalus lentiginosus was found most abundantly along road cuts and in areas where sage Artemesia tridentata had been cleared. C. alexandra females were observed ovipositing on A. lentiginosus growing in the rubble of an abandoned highway. A. miser at Black Canyon, Montrose Co., Colorado, was found in eroded gullies and in sage flats heavily grazed by cattle.
It seems reasonable to assume that Colias alexandra must be a highly mobile species in some parts of its range as it follows the expansion and contraction of populations of its Astragalus foodplant. Evidence from capture-recapture studies at Gothic, Colorado, where alexandra feeds on L. leucanthus, indicates that alexandra has a strong tendency to disperse as compared to the more sedentary Colias meadii Edwards (Ward B. Watt, pers. comm.). It was found from extensive travel over the range of alexandra that this species generally occurred in widely dispersed populations, with occasional local, large concentrations. A "large concentration" was one in which the density of adult alexandra was estimated at 20 or more individuals/100 m2. A large concentration of C. alexandra was nearly always accompanied by a local abundance of a foodplant. A "local abundance" was one in which patches of the foodplant occurred at high densities within small areas that ranged from 100 m2 to several km2. Astragalus canadensis in Idaho was found in densities up to 100 stems/m2 in some patches. In dry areas of Utah, clumps of A. lentiginosus were scattered, but individual plants were often 0.2 m or more wide.
Timber management practices in northen Idaho and Montana offer an explanation for the changes in population size of Astragalus canadensis, and for the spotty occurrence of C. alexandra. Closely related to the Siberian A. uliginosus L., A. canadensis var. mortonii is a conspicuous species, often reaching 0.8 m in height, with a head of greenish-white flowers which later form a cluster of small, erect ellipsoid pods. The outstanding characteristic of canadensis is its occurrence in large patches as a result of vegetative spread by rhizomes. Patches of the species are easily seen while driving at high speeds along the highway. A. canadensis grows most abundantly in lodgepole pine, Pinus contorta Dougl., forest that has just been logged and cleared. Dense stands of
Plant Species
Table 1. Oviposition Records for Colias alexan
Locality
Astragalus miser Dougl. var. oblongifolius (Ryd.) Cron.
(A) COLORADO: Montrose Co., Hwy. 90 above E. Fk. o Creek, Uncompahgre Plateau, S. 2, T. 47N., R 96W. 8100' 29 1971 Ovip. 1100 MST on leaves at tip of stems. (CU) SLE
(B) COLORADO: Montrose Co., Crystal Dam Road, 1 mi. Black Canyon Natl. Mon. Boundary, NE *4 of SE % S. 8, T. R. 7W. 8530' 21 July 1971 Ovip. 1200 MST on leaves. (CU
. Astragalus bisulcatus (Hook.) A. Gray var. haydenianus (Gray)
(A) COLORADO: San Miguel Co., Sand Rock Road, nr Canyon Reservoir, SW y4 of SE y4 S. 9, T. 42N., R. 18W. Uncompahgre Natl. Forest. 12 July 1971 Ovip. 1030 MST on
(CU) SLE
Astragalus lentiginosus Dougl. in Hook.
var, diphysus (Gray) Jones
var. araneosus (Sheld.) Barneby
var. salinus2
(Howell) Barneby
(A) UTAH: Wayne Co. Bull Creek Pass Road, N. Side Mtns. NW 14 of S. 20, T. 30S., R. 18W. 5600' 11 May Ovip. 1030 MST on leaves. SLE
(A) UTAH: Piute Co., Hwy. 153, 1 mi. W. of Junction. 20 June 1972 Ovip. 1130 MST on leaves. (CU) #7219 S
(B) UTAH: Juab Co., Hwy. 6-50, Jericho Turnoff. 5400' June 1972 Ovip. 1200, 1330 MST (CU) #7220 SLE
(A) IDAHO: Twin Falls Co., Magic Hot Springs Road, 4 mi. Rogerson. 4500' 1 July 1972 SLE
(B) IDAHO: Butte Co., 2 mi. NW of Atomic City, Hwy. 26. 6 July 1972 SLE
(C) IDAHO: Cassia Co., Hwy. 77, 0.5 mi. N. of Junction Elba-Malta Road. 5000' 3 July 1972 (CU) #7221 SLE
1 All records followed by (CU) were determined by Dr. W. A. Weber of the University of Colo bers indicate that the plant specimens have been deposited in the C.U. Herbarium collection. Dist were greatly aided by the comprehensive work of Barneby (1964).
2 This variety is inferred to be a foodplant by its association with Colias alexandra populations, a members of the A. lentiginosus complex.
Table 1. (Continued)
Plant Species
Locality
Astragalus eremiticus Sheld. Complex
(A) NEVADA: White Pine Co., Berry Cr., Schell Creek R 7800', Humboldt Natl. Forest 28 June 1972 Ovip. 1530 PST
#7223 SLE
Astragalus canadensis L.
var. mortonii (Nutt.) S. Watson
(A) IDAHO: Kootenai Co., Bunco Cr. Road Cutoff, 0.5 of Farragut State Park on Lake Pend Oreille. 2100' 13 July Ovip. 1000 PST (CU) #7224 SLE
(B) IDAHO: Boundary Co., Intersection Herman Lake Road U.S. Hwy. 2, 3 mi. W. of Montana border. 2500' 16 July 19 assoc. with C. alexandra. (CU) #7225 SLE
(C) MONTANA: Mineral Co., Cabin City Campground R Old U.S. 10, 3 mi. SE of De Borgia. 3300' 23 July 1972 1500 MST (CU) #7226 SLE
Lathyrus leucanthus Rydb.
(A) COLORADO: Montrose Co., 2 airline mi. N. of Buckey ervoir, La Sal Mtns. T. 48N., R. 20 W. 8000' 27 June 1971 1230 MST (CU) SLE
(B) COLORADO: Mesa Co., SOB Creek, 8 mi. W. of Hw Lands End Road, Grand Mesa. 10,000' 7 July 1971 Ovip. MST (CU) SLE
(C) COLORADO: Gunnison Co., base of Crested Butte. 13 July 1967 J. F. Emmel & A. O. Shields (JFE #2, deposited ley Herbarium, Stanford U.)
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canadensis were observed growing in the ashes of burn piles, and in still-visible tractor tracks. Young stands of P. contorta are thinned for optimum growth, and A. canadensis and many other species of herbs cover openings in the thinned forest. A. canadensis becomes much less frequent in mature or stagnant lodgepole pine stands, or in dense Douglas fir, Pseudotsuga menziesii (Mirb.) Franco-Western red cedar, Thuja plicata Bonn, forest. Direct comparisons for butterfly abundance were made between adjacent logged and unlogged stands. C. alexandra was found commonly only where A. canadensis was abundant, although large patches of A. canadensis were found where no C. alexandra were seen. It seems possible that present timber maintenance methods have replaced a natural fire cycle which opened up clearings for invasion of A. canadensis, an early serai stage plant.
The single factor of foodplant abundance as a cause of large alexandra populations is insufficient in itself. Increased nectar sources, and an open habitat for increased adult interaction may contribute to large populations. It was noted that Lycaena mariposa Reakirt, Lycaeides argyrognomen Bergstrasser, and Colias interior Scudder were often extremely common in northern Idaho forest openings where C. alexandra was abundant.
W. H. Edwards discovered that C. alexandra enters a 3rd instar diapause. This may be an adaptation in response to desiccation of the foodplant. In Juab and Piute Counties, Utah, at the end of June 1972, Astragalus lentiginosus var. araneosus was found in an advanced stage of desiccation, with most small plants completely withered. A few large plants, on which C. alexandra was ovipositing, held mature pods on some stems, and were still blooming on others. No new growth was observed, and leaves were hard and leathery. With high evaporation rates and scant rainfall in this part of Utah, the risk of drought is great during the summer months. Even in an area of comparatively high rainfall such as Gothic, Gunnison County, Colorado, C. L. Remington (pers. comm.) has noted that Lathyrus leucanthus withers toward the end of July.
There was little opportunity for field observations on choice of food-plants by alexandra. In most populations where ovipositions were observed, only one species of Astragalus or Lathyrus was found, although search for other species was made. In many areas two or more acceptable foodplants surely must occur within the range of one alexandra population. In the Schell Creek Range of White Pine Co,, Nevada, Barneby (1964) records varieties of Astragalus lentiginosus and A. miser within the area where alexandra was found ovipositing on A. eremiticus. In Cassia County, Idaho, at 5000 ft. on 3 July 1972, C. alexandra was
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found abundantly in a small field (75 X 75 m) of alfalfa, Medicago sativa L. Between 1000 and 1200 MST alexandra was estimated at a density of 150-200 individuals in the field at one time. Such large numbers of this species had not been encountered previously, and it occurred to me that alexandra might be using Medicago as a foodplant in this locality. Careful observation of nearly thirty females during the prime oviposition time of late morning revealed only nectar-seeking behavior, and no oviposition or courtship behavior. Scattered Astragalus lentiginosus var. salinus plants were found along the road cut, and among sage shrubs bordering extensive sage and juniper flats. This discovery led me to believe that the source of the alexandra population was a colony of the Astragalus growing in the sage flats, with alexandra adults moving into the alfalfa field to feed.
Voltinism. Colias alexandra is a univoltine species over most of its range. Emergence times vary for different populations, with western Colorado ones generally appearing several weeks before those in the Great Basin, Arizona, and in the northern Rockies. Lengths of emergence vary from 3 weeks in populations from dry areas in western Colorado to 2 months along the Front Range in eastern Colorado.
Mike Fisher discovered a bivoltine alexandra population on the high plains near Parker, Douglas Co., Colorado. Confining dates for the two broods are, first brood: 25 May-22 June; second brood: 25 July-19 August, with no stragglers between broods. C. alexandra oviposited on Oxytropis lambertii in this area, although Astragalus species may be used as well.
Interspecific Relationships with other Colias. Throughout its range C. alexandra is almost always sympatric with at least one other species of Colias, and in some areas up to four. C. alexandra and C. philodice are most often sympatric, although the peaks of their broods are not always synchronous. Ae (1959) states that in Colorado opportunities for interspecific mating are rare between widespread Colias species (philodice and eurytheme) and the "northern" species (alexandra, scud-deri Reakirt, and meadii) due to seasonal isolation. In western Colorado, the peak of alexandras flight period occurs between the spring and summer broods of C. philodice. On Mesa Verde, Montezuma Co., on 26 May 1972, the alexandra-.philodice ratio was 5:1, and on 16 July 1971 in the same locality, the same ratio was 1:8. In Cassia Co., Idaho, in an alfalfa field on 3 July 1972, the alexandra-.philodice ratio was in the range of 100:1, with no C. eurytheme seen. In western Colorado C. eurytheme is quite rare when C. alexandra flies in late June, but becomes more common after alexandra disappears. Throughout the Great Basin alexandra flies with both C. eurytheme and philodice, and
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in northern Idaho is sympatric with C. interior as well. Near Lake Pend Oreille, Kootenai Co., Idaho in thinned lodgepole pine forest on 14 July 1972, Colias collections were made along a 0.2 mile strip of logging road from 0900 to 1200 PST. In this limited area nearly 200 C. alexandra were seen and collected, as well as 10 C. interior, 6 C. eurytheme, and 2 C. philodice (all specimens seen of the last 3 species were collected). Several unsuccessful attempts by alexandra males to copulate with interior females were observed in this locality. Where alexandra and interior are sympatric, alexandra frequents open areas along roadways and meadows, while interior is found more often in the shade of pine woods. C. interior invades meadow habitats in localities where interior is more common than alexandra.
In Canyon Creek Canyon, Ochoco Mountains, Crook Co., Oregon, where C. alexandra and C. occidentalis Scudder are sympatric, A. O. Shields (in litt.) notes that the two species are easily separable on the wing, and that there are other behavioral differences. C. occidentalis "was more confined to openings and edges of woods than alexandra, though both taken commonly in open, broad meadows." In Canyon Creek Canyon on 10 July 1970, Shields observed oviposition by C. occidentalis on the leaf underside of Lathyrus lanszwertii Kell. (Shields #109, det. J. T. Howell, Calif. Acad. Sci.). Shields saw a species of lupine Lupinus latifolius J. G. Agardh. (Shields #86) in Canyon Creek Canyon, the same foodplant species used by C. occidentalis at Camp Ellen-dale, Glenn County, California.
Adult Nectar Sources. A study of nectar sources for several populations of C. alexandra indicates that the insect visits a variety of plant species. Throughout western Colorado and parts of Utah the greatest concentrations of alexandra were found on various species of thistle Cirsium (Compositae). One large population on the South Rim of the Black Canyon, Montrose Co., Colorado, was found almost exclusively on Canadian thistle, Cirsium arvense L. This plant population had been introduced during the previous five years after the construction of a new road. On 29 June 1971, on the Uncompahgre Plateau, Montrose Co., Colorado, alexandra was observed to ignore Cirsium sp. in favor of mules ears, Wyethia arizonica Gray (Compositae). In Cassia Co., Idaho, alexandra chose the blossoms of Medicago sativa and bindweed Convolvulus arvensis L. (Convolvulaceae) over those of a Chrysothamnus species (Compositae) which attracted Satyrium fuliginosum Edwards, Speyeria zerene Boisduval, Cercyonis oetus Boisduval, and Hesperia harpalus Edwards. In northern Idaho, Cirsium sp. was completely ignored, and alexandra was found most commonly on its foodplant, Astragalus canadensis var. mortonii.
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Nectar sources are especially significant in concentrating alexandra populations in arid country. The widespread introduction of weeds, especially Cirsium sp., along roadcuts may have local effects on the density of alexandra populations. At Jericho Turnoff from Hwy. 6-50, 5400 ft., Juab Co., Utah on 25 June 1972, C. alexandra was collected on two small thistle patches (tentatively identified as Cirsium vulgare L.) along an abandoned highway. This locality was extremely arid, with extensive sage flats changing to sand dunes a few miles to the west. No moisture in the form of mud or streams was available. The only other nectar sources utilized in this area were a few scattered blossoms in Astragalus lentiginosus clumps, and the flowers of a small introduced mint growing on the roadcut. It appeared that the thistle patches were recent introductions, owing to the lack of previous years' stalks, and the absence of other thistles for many miles in all directions. Twenty-five C. alexandra were collected on thistle flowers from the two patches. A return to the area the next day netted only four specimens. Subsequent travel north, south, and west for several miles in each direction indicated that alexandra was either very scarce, or non-existent beyond 0.2 mi. from the thistle patches, although scattered A. lentiginosus clumps were seen along the Little Sahara Sand Dunes road to the west of Jericho. It appeared that we had collected nearly the entire emerged population from a large area, indicating that the thistle blossoms were a powerful attractant. This observation raises the question of whether adult nectar sources may be a limiting factor in the size of arid-land alexandra populations. In some areas, alexandra may be limited to the flowers of its foodplant, a situation shared by some desert-dwelling Philotes, and Apodemia mormo Felder & Felder, which feed on fall blooming Eriogonum species (Polygonaceae).
Behavior. Colias alexandra followed a consistent behavioral pattern over its range. In open country on warm days individuals of both sexes arrived at nectar sources about 1030. Males were least wary at this time, and most easily collected. After 1200, both sexes began to leave the nectar sources. Males congregated on mud, or flew continuously over meadows or along the edge of the forest. Oviposition by females occurred most often between 1000 and 1330. The fast flight and large size of alexandra made it easy to separate from other Colias species on the wing. Beak-marked individuals were very rare, and no attacks by avian predators were observed. Although hundreds of alexandra were observed on nectar sources, no copulating pairs were found. This suggests that courtship and mating may take place at a distance from nectar sources. C. alexandra moved away from open areas during the hottest hours of the afternoon, and then another brief nectar feeding
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period occurred in some populations at 1600. On the Uncompahgre Plateau in San Miguel Co., Colorado, an individual was flushed from inside a sagebrush clump at 0800 MST where it had apparently spent the night.
Summary
1. Colias alexandra oviposits on members of at least four genera of the Leguminosae: Thermopsis, Astragalus, Oxytropis, and Lathyrus. Lupinus is considered a very doubtful foodplant. Clover, Trifolium repens, is known to be a laboratory host. Field observations indicate that alfalfa, Medicago sativa, is an unlikely foodplant.
2. C. alexandra oviposited on two species of Astragalus, and one of Oxytropis which are known to be toxic to livestock. At least one species, Astragalus bisulcatus, is known to be a selenium accumulator.
3. C. alexandra foodplants are characteristically perennial, and show a scattered or patchy distribution. Several are dependent on the availability of disturbed plant communities and early serai stages in forests for their optimum growth. Two species, Thermopsis divaricarpa and Astragalus canadensis, form dense patches due to spread by rhizomes.
4. C. alexandra occurs most frequently in widely dispersed populations. Occasional large, local concentrations are found. It is suggested that these large, local alexandra populations are primarily dependent on the local abundance of a foodplant. Other factors such as an open habitat and increased nectar sources may contribute to the support of large alexandra populations.
5. Although univoltine over most of its range, a bivoltine alexandra population is known from the High Plains-Front Range contact area in Douglas Co., Colorado.
6. C. alexandra is nearly always sympatric with one or more species of Colias. Limited data suggest that there are temporal and behavioral differences between alexandra and other species of Colias.
7. Available nectar sources, particularly introduced weeds, may strongly influence density and size of alexandra populations occurring in very arid areas.
Acknowledgments
The author is grateful to Arthur C. Allyn and Lee D. Miller of the Allyn Museum of Entomology, Sarasota, Florida, and to John M. Burns of the Museum of Comparative Zoology, Harvard University, whose support made travel and research possible during the summers of 1971 and 1972. F. M. Brown and A. B. Klots generously read and commented
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on a previous draft of this paper. The ready willingness of W. A. Weber of the Colorado University Herbarium to make plant determinations is greatly appreciated. Conversations with J. M. Burns, C. L. Remington, and W. B. Watt provided valuable insights. R. Chehey, J. F. Emmel, M. S. Fisher, K. Johnson, J. Scott, and A. O. Shields freely gave helpful field observations on Colias. Special thanks go to my wife Lydia Thompson, whose assistance in the field was invaluable.
Literature Cited
Ae, S. A. 1959. A study of hybrids in Colias (Lepidoptera, Pieridae). Evolution 13:
64-88. Barneby, R. 1964. Atlas of North American Astragalus. Mem. N.Y. Botan. Garden:
13. 2 vol. iii + H88 p. Edwards, W. H. 1873. Butterflies of North America. Vol. 1. Supplementary
Notes. Amer. Entomol. Soc, Philadelphia. 215 p., 50 pis. ----------. 1897. Butterflies of North America. Vol. III. Supplementary Notes.
Houghton Mifflin, Boston, viii + 432 p., 51 pis. Ehrlich, P. & A. Ehrlich. 1961. How to Know the Butterflies. Brown, Dubuque,
Iowa. 253 p. Ferris, C. D. 1972. Notes on certain species of Colias (Lepidoptera: Pieridae)
found in Wyoming and associated regions. Bull. Allyn Mus. Entomol. 5. ----------. 1973. A revision of the Colias alexandra complex (Pieridae) aided by
ultraviolet reflectance photography with designation of a new subspecies.
J. Lepid. Soc. 27: 57-73. Hovanitz, W. 1950a. The biology of Colias butterflies. I. The distribution of
the North American species. Wasmann J. Biol. 8: 49-74. ----------. 1950b. The biology of Colias butterflies. II. Parallel geographical variation of dimorphic color phases in North American species. Wasmann J. Biol.
8: 197-219. Klots, A. B. 1951. A Field Guide to the Butterflies. Houghton Mifflin, Boston.
xvi + 349 p. Masters, J. H. 1970. Concerning Colias eurytheme alberta Bowman (Pieridae).
J. Res. Lepid. 9: 97-99. McDunnough, J. 1922. Notes on the Lepidoptera of Alberta. Can. Entomol. 54:
134-141. Shields, O. A., J. F. Emmel & D. Breedlove. 1969. Butterfly larval foodplants
records and a procedure for reporting foodplants. J. Res. Lepid. 8: 21-36.