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COSEWIC assessment and update status report on the mormon metalmark in Canada

General

The Mormon Metalmark has one generation per year in Canada.  Adults typically fly from early August until mid-September (Guppy and Shepard 2001).  Flight is swift and direct, and is restricted to short distances, usually to nearby host or nectar plants.  Perching individuals hold the wings in a variety of orientations from open to closed, with a half open position being common.  When nectar sources are rare, several individuals may be found on the same plant (St. John pers. obs.). 

Reproduction

Males perch on hillside shrubs and nectar sources to await females (Arnold and Powell 1983, Scott 1986).  In British Columbia, mating pairs were observed within three days of the appearance of adults on the wing (St. John, pers. obs.). In California, males of the endangered subspecies A. m. langei studied by R. A. Arnold and J. A. Powell (1983) eclosed a few days prior to females.  Eggs were laid on the hostplant singly or in clusters of 2-4 on leaves, stems, or inflorescences (Arnold and Powell 1983).

Reproductive factors, which may affect colonization ability and effective colony size, such as duration of the oviposition period and average fecundity, are unknown.  Spermatophore counts of 2.60 per female in A. m. langei (Arnold and Powell 1983) suggest multiple mating by females may be common in this species.

Survival and physiology

Adult life span of A. m. langei in California averaged about nine days in males and 11 days in females (Arnold and Powell 1983).  If these estimates apply to the Canadian populations, they suggest a staggered emergence over a period of about 3-5 weeks.  Nothing is known about survivorship of other stages of the life cycle for any taxon in this species.  Early instar larvae hibernate inside inflated stems of E. inflatum or dried flower heads of E. fasciculatum, or in litter near the hostplant (Scott 1986).  Ballmer and Pratt (1988) found partially grown larvae of A. mormo on hostplants during winter, and observed feeding in another riodinid, Calephelis nemesis, whenever afternoon temperatures exceeded 12.8ºC.

Late instar larvae are nocturnal feeders in the southern part of their range (Arnold and Powell 1983) and rest during the day in nests of leaf litter held together with silk (Ballmer and Pratt 1988).

It is not known whether eggs hatch in fall or spring in the Canadian populations, or whether mature larvae are also nocturnal in Canada.

Movements/dispersal

Arnold and Powell (1983) have made the only quantitative study of dispersal, in the endangered subspecies, A. m. langei, in California.  Adult butterflies dispersed an average of 9 m for males and 11 m for females, with maximum distances to about 600 m. Females moved greater distances per unit time than males (average Vagility, female: Vf=22.2-47.7 m/day, males Vm=10.4-27.5 m/day).  Males were also more concentrated and females more dispersed. 

Casual field observations of the species in British Columbia and Saskatchewan suggest that individuals in the Canadian populations also confine themselves to very limited dispersal over the adult lifespan (St. John & Hooper, pers. obs.).  Nothing is known about dispersal in the larval stage, but it seems unlikely that larvae move between hostplants. 

Nutrition and interspecific interactions

In both Saskatchewan and British Columbia, the flowering season of the buckwheat hostplants corresponds closely to the flight period of the butterfly, whereas other common buckwheat species bloom considerably earlier.

In Saskatchewan, E. pauciflorum begins to bloom in June on clay soils on flats.  By August and early September, the plants on flats dry up, but those on the arid hillsides come into bloom and are visited by metalmarks.  Mormon Metalmarks were seen nectaring exclusively on branched umbrella-plant during the first three weeks of observing. They were only found on rabbitbrush when the umbrella-plant flowers were deteriorating (Hooper pers. comm.).

In both provinces, adult metalmarks nectar on rabbitbrush as well as on buckwheats.  In British Columbia, rabbitbrush appears to be polyphenic for flowering time, with some individuals coming into bloom as early as late June while many others continue to flower into mid-October.  The presence of early and late flowering rabbitbrush, in addition to buckwheat, may be necessary to provide adequate nectar throughout the metalmark flight period.  Like buckwheats, rabbitbrush appears to require a moderate disturbance regime for its continued presence.  At many sites in the southern interior of British Columbia, both species are abundant along roadcuts and largely absent from adjacent, less disturbed hillsides (St. John pers. obs.).

In British Columbia, the larval hostplant of metalmarks, Eriogonum niveum, has a late summer flush of vegetative growth that produces basal clusters of young leaves which overwinter while partially grown.  The other common species of buckwheat (E. heracleoides Nutt.), which often occurs in similar habitats, lacks this autumnal growth flush (St. John pers. obs.), is not known to be used by metalmarks (Guppy and Shepard 2001), and was absent from all but one butterfly colony site.

Behaviour/adaptability

There is a strong association of these butterflies with the larval foodplant.  Adults also use the same buckwheat species and rabbitbrush as nectar sources and perching sites.  The base of the buckwheat hostplants also serves as a protected site for the larvae in periods of inactivity and during hibernation (Arnold and Powell 1983).  Given this concentration of resources and the metalmark’s sedentary habits, the butterfly is probably very sensitive to changes in the distribution and density of suitable habitat patches in its environment.  All the species of endangered butterflies studied by Arnold and Powell (1983) in California shared the traits of dependence on one or two plant species and limited flight movements. This contrasts strongly with the lack of specific microhabitat association and much greater vagility found in more widespread butterfly species (Scott 1975, Sharp et al 1974).