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Recovery Strategy for the Island Blue* (Plebejus saepiolus insulanus) in Canada (Proposed)


Appendix 1. Background

Greenish Blue insulanus subspecies (Plebejus saepiolus insulanus Blackmore) is a subspecies of the Nearctic butterfly species P. saepiolus (Boisduval), the Greenish Blue, in the family Lycaenidae, which includes the blues, hairstreaks, and coppers. Seven subspecies of Plebejus saepiolus are described, two of which occur in British Columbia (B.C.): Greenish Blue insulanus subspecies, and Greenish Blue amica subspecies, Plebejus saepiolus amica (W.H. Edwards). Greenish Blue insulanus subspecies is considered endemic to southern Vancouver Island, B.C. (Guppy and Shepard 2001). The amica subspecies occurs from Yukon to Labrador and south through the mountains of California and Arizona (Layberry et al. 1998). In B.C., Plebejus saepiolus amica occurs throughout the province except on the coast (Guppy and Shepard 2001).

Canadian lepidopterists recognize Greenish Blue insulanus subspecies as a separate subspecies confined to southeastern Vancouver Island (Layberry et al. 1998; Guppy and Shepard 2001). In the United States, Scott (1986) shows the subspecies Plebejus saepiolus insulanus as being more widespread and having a range from northwestern California to southwestern B.C. (Vancouver Island only), Montana, Colorado, Nevada, and Utah. Hinchliff (1994) applies Plebejus saepiolus insulanus to a few populations that occur only within Oregon. Until the taxonomic uncertainty surrounding the butterfly can be resolved, Greenish Blue insulanus subspecies is recognized as a distinct subspecies occurring only on Vancouver Island and found nowhere else in Canada (COSEWIC 2000).

The most recent records of Greenish Blue insulanus subspecies are from Mount Malahat (1979), Mount Arrowsmith (1962, 1963), and Mount Finlayson (1960). Although the subspecies has not been recorded since 1979, surveys of potential habitat are incomplete and unconfirmed sightings are periodically reported (J. Heron, pers. comm., 2006; L. Ramsay, pers. comm., 2006). No extant populations are known (J. Heron, pers. comm., 2006).

Species Assessment Information from COSEWIC

Scientific Name: Plebejus saepiolus insulanus

Common Name: Greenish Blue (Island Blue under COSEWIC)

Present Status in Canada and Year of Designation: Endangered, 2000

Range in Canada: British Columbia

Rationale for Status: An extremely restricted endemic of southern Vancouver Island, this species was last recorded in 1979. There remains a remote possibility that it still persists in poorly surveyed habitat.

Description of the Species

Current taxonomic literature (Layberry et al. 1998; Guppy and Shepard 2001) provides no diagnostic characters for the morphological separation of Greenish Blue insulanus subspecies and amica subspecies. Figures 1a-c show photographs of Greenish Blue insulanus subspecies taken from specimens deposited at the Spencer Entomological Museum at the University of British Columbia. The following is a general description of adults of the Greenish Blue, provided here as there are no written descriptions of the subspecies itself. The wingspan is 2.1–2.8 cm. The dorsal wing surfaces of the females are dark brown with a bluish metallic sheen and the hindwing margins have a row of black spots with orange caps. The ventral wing surfaces of the female are pale tan to dark grey. The dorsal wing surfaces of the male are metallic blue and have a row of dark spots on the hindwing margins. The ventral wing surfaces are bluish towards the base of the wings and gradually turn silver-grey towards the margins. Both wings have two rows of black spots. The male hindwings have orange caps on the second row of spots that are directed towards a partial third row of spots, with one spot distinctly larger along this row. Both sexes have a distinct black bar in the dorsal forewing.

Figure 1a. Greenish Blue insulanus subspecies, dorsal surface (male). Photo: J. Heron.
Figure 1a. Greenish Blue (insulanus) subspecies, dorsal surface (male). Photo: J. Heron.

Figure 1b. Greenish Blue insulanus subspecies, ventral surface (female). Photo: J. Heron.
Figure 1b. Greenish Blue (insulanus) subspecies, ventral surface (female). Photo: J. Heron.

Figure 1c. Greenish Blue insulanus subspecies ventral surface. Photo: J. Heron.
Figure 1c. Greenish Blue (insulanus) subspecies, ventral surface. Photo: J. Heron.

The eggs of Greenish Blue insulanus subspecies have not been taxonomically described but are likely similar to those of other subspecies of the Greenish Blue, i.e., greenish-white and laid singly among host flowers (Sharp and Parks 1973; Layberry et al. 1998).

Taxonomic descriptions of the larvae of Greenish Blue insulanus subspecies have not been published; however, a photograph of the amica subspecies is published in Guppy and Shepard (2001). Greenish Blue insulanus subspecies larvae are likely similar to Greenish Blue larvae. Greenish Blue larvae are an overall light lime green with white hairs dorsally and laterally, a purplish front or red rear, and a lateral pair of white lines paralleled by a row of white dots (Scott 1986).

The life cycle of Greenish Blue insulanus subspecies is not well known. There is one generation per year. Adults fly from late May through early August, depending on locality (COSEWIC 2000), elevation and latitude (Scott 1986). Late season records are usually of females at higher elevations (COSEWIC 2000). Greenish Blue adults are active in June and July; tend to remain near host plants, and have been noted perching on flowers and sedges within bog areas (Christensen 1981; Pyle 1986; Layberry et al. 1998; Guppy and Shepard 2001). Scott (1986) notes that adults are local to the host, sipping mud and flowers of Trifolium. Males patrol for females near host plants.

Details of Greenish Blue insulanus subspecies overwintering, egg development and hatching, and larval development are unknown (COSEWIC 2000), but likely are similar to what has been observed for the Greenish Blue. TheGreenish Blueoverwinters as an immature larva (Ferris and Brown 1980; Scott 1986; Guppy and Shepard 2001) and other species of Plebejus overwinter as eggs or early instar larvae. Thus, Greenish Blue insulanus subspecies eggs and larvae may be found on the host plant for extended periods.

Populations and Distribution

Greenish Blue insulanus subspecies is endemic to Vancouver Island, B.C., where it has been recorded from Saratoga Beach near Campbell River south to Victoria (Figure 2). No records of this subspecies are known from outside this area (Jones 1951; COSEWIC 2000). Existing data are insufficient for estimates of population and distribution trends. The subspecies was last recorded in 1979 (COSEWIC 2000; B.C. Ministry of Water, Land and Air Protection 2004). Future inventory may find unknown or presumed-to-be-extirpated populations.

The global rank is G5TH (i.e., Plebejus saepiolus is globally secure, while P. saepiolus insulanus subspecies is possibly extinct; NatureServe Explorer 2007).

The provincial rank is SH (i.e., possibly extinct) and the subspecies is Red-listed by the B.C. Conservation Data Centre (2007).

Figure 2. Historical distribution of Greenish Blue insulanus subspecies in British Columbia. Map: Ministry of Environment.
Figure 2. Historical distribution of Greenish Blue (insulanus) subspecies in British Columbia. Map: Ministry of Environment.

Needs of the Greenish Blue insulanus subspecies

Habitat and biological needs

Greenish Blue insulanus subspecies historic records are from disturbed areas including roadsides, old campgrounds, cloverbanks along open streams, and similar habitats. The most recent records are from higher elevations including subalpine areas (COSEWIC 2000). Native clovers, thought to be the host plants, require continual moisture and sunlight. It is unclear if Greenish Blue insulanus subspecies can subsist on non-native clover species. In the Pacific Northwest, other subspecies of the Greenish Blue typically are found in open areas with clovers such as bogs, woodland openings, and mountain meadows.

Food plant specificity of Greenish Blue insulanus subspecies is unknown although it is likely that the subspecies uses native or non-native clovers (Trifolium spp.) (Emmel and Emmel 1973) as do other subspecies of the Greenish Blue. Clovers are low-lying perennials of the family Fabaceae found in moist places at low to middle elevations (Pojar and MacKinnon 1994). Oviposition and larval development in many species of Plebejus (including the Greenish Blue) occur in the flower heads of legumes, especially clovers (Layberry et al. 1998; COSEWIC 2000; Guppy and Shepard 2001).Greenish Blue has been recorded feeding on native Springbank Clover (T. wormskjoldii Lehn.) (Scott 1986), which occurs on Vancouver Island. In eastern Canada, amica spp. larvae feed on introduced white (T. repens L.) and alsike clover (T. hybridum L.) but apparently do not feed on introduced red clover (T. pratense L.) (Christensen 1981; Layberry et al. 1998). Larvae of Greenish Blue feed upon both flowers and fruits and are typically found within the flower heads. Similar behaviour is probable for Greenish Blue insulanus subspecies. Scott (1986) also suggests Greenish Blue may feed upon Lotus species, another genus in the pea family, once clovers senesce. Within southern Vancouver Island, eight Lotus spp.occur: five are native and three are introduced. These plants occur within grassy meadow habitats, roadsides, pastures, and clearings – similar habitats to that of Greenish Blue insulanus subspecies. Greenish Blue insulanus subspecies has not been documented feeding on Lotus spp.

Most species of Plebejus overwinter as eggs or first- or second-instar larvae (Ferris and Brown 1980; Guppy and Shepard 2001). It is not known in what life stage Greenish Blue insulanus subspecies overwinters.

Ecological role

Adult butterflies are minor plant pollinators. Many Lycaeninae butterflies (a subfamily of Lycaenidae) are obligatorily or facultatively associated with ants (Pierce and Elgar 1985; Pierce et al. 2002). The specific ecological role of Greenish Blue insulanus subspecies is unknown.

Limiting factors

Host plant specificity

On Vancouver Island, as elsewhere (COSEWIC 2000), native clovers have possibly been outcompeted, have been replaced by non-native plants, and thus are no longer common. If the subspecies’s only food plants are native clovers, limited host plant resources would limit populations of Greenish Blue insulanus subspecies. In other parts of the species’ range, subspecies of Greenish Blue are known to be polyphagous and will subsist upon non-native clovers, and as suggested in Scott (1986), on Lotus spp. Greenish Blue insulanus subspecies has only been recorded in association with native clovers and possibly depends upon these plants alone. However, research into polyphagy is necessary to clarify this limiting factor.

Dependency on ant species

Greenish Blue insulanus subspecies belongs to the subfamily Lycaeninae, some members of which have obligate or facultative relationships with ants (Pierce et al. 2002). It is unknown if Greenish Blue insulanus subspecies is an ant associate.

Threats

Greenish Blue insulanus subspecies has not been observed or recorded since 1979 and threats to the subspecies are undocumented and unknown. The list below is of potential threats based on experience with at-risk species occurring within parts of Greenish Blue insulanus subspecies historic range (GOERT 2006). These activities and processes may have contributed to degradation or loss of habitat or populations in the past, and could threaten populations.

Description of threats

The following are considered to be threats, assuming that populations of Greenish Blue insulanus subspecies exist:

  1. Invasive and exotic species. Their introduction and encroachment threaten native host plant species, and change ecosystems (GOERT 2006). It is unknown if Greenish Blue insulanus subspecies populations may be able to subsist on non-native clovers, and if host plant switching is possible.
  2. Habitat destruction. Most ecosystems of southern Vancouver Island that contain suitable Greenish Blue insulanus subspecies habit occur primarily on private land and are under development pressure. Suitable habitat is becoming increasingly fragmented and species that depend upon these ecosystems are increasingly vulnerable to natural threats including disease and predation, inclement weather, and effects of forest succession (e.g., see GOERT 2006).
  3. Recreational use. Historic locations for Greenish Blue insulanus subspecies are periodically used for recreational purposes including hiking, camping, pet exercise, mountain biking, and some all terrain vehicle use.
  4. Btk spray. Some parts of southern Vancouver Island, the adjacent Gulf Islands, and the mainland are periodically sprayed with the biological control agent Btk (Bacillus thuringiensis var. kurstaki), to eradicate introduced populations of European or Asian Gypsy Moths (Lymantria dispar L.). Btk is a naturally occurring bacterium that, at certain concentrations, is pathogenic to feeding butterfly and moth larvae. Aerial or ground sprays are highly effective in controlling gypsy moths but will also affect caterpillars of non-target species feeding within spray zones.
  5. Climate change. The effects of climate change on Greenish Blue insulanus subspecies are unknown but may seriously impede the recovery of this taxon. Studies on other butterfly taxa indicate an overall threat to this group (J. Hellmann, pers. comm., 2006).
  6. Collecting. Butterfly enthusiasts may want to collect specimens of Greenish Blue insulanus subspecies. Specimens should not be collected for reasons other than research. Specimens collected should be reported to the B.C. Conservation Data Centre and deposited in the Royal British Columbia Museum or the Canadian National Collection of Insects and Arachnids. Collecting individuals of Greenish Blue insulanus subspecies is illegal on federal lands because the species is listed as Endangered in the Species at Risk Act (SARA). Any collection activities should only occur if essential to the recovery of the species and only by qualified government personnel or those individuals issued a collection permit from the appropriate authority.

Actions Already Completed or Underway

  • Survey of potential habitat of Greenish Blue insulanus subspecies in subalpine areas of southern Vancouver Island (B.C. Ministry of Water, Land and Air Protection 2004). No populations of the subspecies were found during this survey.
  • Status of Five Butterflies and Skippers in British Columbia (Shepard 2000). Southern Vancouver Island and the adjacent Gulf Islands were surveyed for at-risk butterflies. No populations of Greenish Blue insulanus subspecies were found.
  • Southeastern Vancouver Island Garry oak meadows. Repeated annual surveys of seven meadows from Victoria to Hornby Island have found neither Greenish Blue insulanus subspecies nor native clover specimens (J. Hellmann, pers. comm., 2006).

Knowledge Gaps

Little is known about Greenish Blue insulanus subspecies life history, habitat requirements, potential threats, and distribution. In the absence of known populations, most knowledge gaps cannot be filled. Determining if populations of Greenish Blue insulanus subspecies exist is the first priority. Should populations be located, habitat and other biological knowledge gaps (including description and assessment of threats) should be addressed to define management activities for population protection and maintenance. Clarification of the subspecies taxonomy within Plebejus saepiolus is a knowledge gap.