Half-moon hairstreak (Satyrium semiluna) COSEWIC assessment and status report: chapter 8
Biology
Life cycle and reproduction
Eggs are laid on host lupines or in the leaf litter at the base of plants (Scott 1986b, 1992). The eggs overwinter and the larval and pupal stages occur in spring. Adults emerge in the late spring or early summer and complete the life cycle. The species is reported as having one generation per year.
Adult activity period
In British Columbia, adults have been found as early as 20 May and as late as 4 July. Based on observations in 2003 and most museum specimens, the last two weeks of June appear to be the peak flight period in British Columbia. Capture dates for five museum specimens from the period 1895 to 1901 are notably earlier and range from May 20 to June 2. Lack of precise geographic locations for these specimens makes it impossible to determine if these early dates were the result of unusual climatic conditions at that time or if the specimens originated from low elevation habitat which no longer exists.
An early specimen from the Alberta population was collected on 25 June (Bird et al., 1995). In Kondla’s 2003-2004 surveys, the Alberta population flew in the last two weeks of July. The flight period in both provinces appears to be correlated with seasonal senescence of Lupinus sericeus.
In both British Columbia and Alberta, adults were active during much of the daylight period. In 2003, adults were active between 0830 and 1800 hours in British Columbia and between 0830 and 1930 hours in Alberta (Kondla, personal observation). British Columbia individuals may engage in some communal roosting overnight at the tops of sagebrush plants. Three individuals were noted within a few centimetres of each other at the top of a sagebrush plant at 1800 h on one occasion. In 1975, Guppy (unpublished data) noted many adults resting individually, with their wings closed, on the upper surface of large arrowleaf balsamroot (Balsamorhiza sagittata) leaves at midday in hot weather with the sun mostly obscured by high thin cloud.
Adult food resources
Albertaadults primarily use Eriogonum flavum as a nectar source, probably because of the abundance of this plant in its habitat. Flowers of Solidago missouriensis are also used as a nectar source, but this plant is much less abundant in the habitat (Kondla 2003a, 2004b). British Columbia adults have been found taking nectar at Achillea millefolium, Eriogonum heracleoides, and rabbitbrush (Chrysothamnus viscidiflorus) (Kondla 2003b and unpublished data).
Reproductive behaviour
Perching appears to be the primary form of mate-locating behaviour exhibited by males in both Alberta and British Columbia.
In Alberta, several mating pairs of S. semiluna were found on flowers of both Eriogonum flavum and Solidago missouriensis. It is possible that nectar sites also serve as mate-locating sites. Mating pairs have also been noted on Lupinus, pasture sagewort (Artemisia frigida) and other vegetation. Under conditions with little or no wind, Alberta males engage in low (less than 60 cm high) patrolling flights which include circling of Lupinus plants. Both males and females have also been seen on a variety of substrates, including bare soil, grass culm, rocks, dry knapweed stalk, aster (Aster sp.), silverberry (Eleaegnus commutate), Lupinus sericeus, cinquefoil (Potentilla sp.) and milk-vetch (Astragalus sp.) (N. Kondla 2003a, 2004b).
In British Columbia, male S. semiluna were commonly found perching on big sagebrush (Artemisia tridentate) shrubs. They were also observed making short flights at heights of 1 to 2 metres between shrub perches. These flights sometimes included circling a given sagebrush plant two or three times before the male moved on to another plant and settling into a perch (N. Kondla, unpublished data).
Larval resources
Larvae in the United States have been reported to feed on various species of Lupinus (Ballmer and Pratt 1988, Scott 1986b, 1992). Several species of Lupinus are known to occur in Alberta and British Columbia, but only the widespread and common Lupinus sericeus has been consistently noted where S. semiluna populations have been found (Kondla, unpublished data).
Interspecific interactions – Myrmecophily
Myrmecophily in butterflies is a mutualistic relationship between the larva and one or several ant species. The larvae of lycaenid butterflies secrete a nutritious liquid containing carbohydrates and free amino acids from a dorsal gland (Pierce 1987, Leimar and Axtén 1993). These secretions are eagerly consumed by the attendant ants. In return, the ants guard the larvae from attacks by predators and parasitoids.
Among Lepidopterans, myrmecophily is most prevalent among Lycaenid butterflies. More than 50% of the butterfly species within the family have a relationship with ants during larval development (Seufert and Fiedler 1996). Some Lycaenid species are obligates (they cannot survive without ant attendants, usually of a specific ant species). Others are facultative (the caterpillar can interact with different ant species, but can survive without them). However, even among facultative species, the larvae usually gain an advantage from myrmecophily.
Myrmecophily in North American Lycaenid species has been noted by a number of researchers, including Ballmer and Pratt (1988) and Scott (1992). Many species in the family Lycaenidae form obligatory associations with certain ant species. In California, the larvae of S. fuliginosa (and presumably S. semiluna) are frequently tended by at least three species of ants (Warren, 2005). It is not known if myrmecophily is a factor in Canadian populations of S. semiluna, but if these populations are strongly myrmecophilous, then this ant association might help explain the apparently patchy distribution of the butterfly within larger areas of otherwise seemingly suitable habitat.
Adaptability
The presence of a British Columbia population of S. semiluna in an area that is fairly heavily grazed by livestock suggests that the butterfly is at least somewhat tolerant of that land use. The lack of a consistent association of the butterfly with any lupine other than Lupinus sericeus, combined with the patchy distribution within apparently suitable habitat, suggests that S. semiluna may be quite specialized and not very adaptable. Alternately, it may be that the attendant ants have a patchy distribution that limits the butterfly.
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