Conservation Biology of Lycaenidae (Butterflies) - IUCN

host races in North American lycaenids, recent work details a
genetic basis for larval hostplant preferences by adult butterflies
in the rather sedentary nymphalid genus Euphydryas. Singer
and colleagues have found significant differences in patterns of
oviposition preference and tolerances for hostplants among
phenotypically and geographically distinct populations,
suggesting distinct adaptation at the population level (see
Singer 1971; White and Singer 1974; Rausher 1982). More
recently, Singer and colleagues have documented the existence
of genetically based (i.e. heritable) differences between adjacent
populations and within polyphagous populations (Singer 1983;
Singer et al. 1988).
Species in the lycaenid genus Euphilotes exhibit similar
patterns in the use of larval hostplants, thereby suggesting the
possibility of genetic differentiation among populations for
hostplant tolerance (see Pratt and Ballmer 1986). In southern
California, Euphilotes enoptes (Behr) has been found to feed on
five species of Eriogonum; the butterfly is monophagous at
some locations, while it is polyphagous in others, with clear
host preferences.
Association with ants
Roughly half of the lycaenid species world-wide associate with
ants, and their larvae possess numerous distinctive structures
that facilitate these interactions (Downey 1962; Atsatt 1981;
Pierce 1987). Although a few of these associations are
antagonistic, with butterfly larvae preying on ant brood (Cottrell
1984), the majority appear to be mutualistic (Pierce 1987).
Lycaenids vary greatly in terms of their degree of dependence
on ant associates and their degree of specificity for particular
ant species.
We propose that butterfly species which associate with ants,
and particularly those species with strong dependence on them,
are far more sensitive to environmental changes and thus more
prone to endangerment and extinction, than species that are not
tended by ants. While this hypothesis remains untested, it seems
probable because of two factors. First, such species
simultaneously require the right food plant and the presence of
particular ant species – a combination that occurs infrequently.
These dual requirements of tended species should result in
spatial distributions that are patchier than those for untended
species. The degree of patchiness should increase as dependence
and/or the species specificity of lycaenids increase. Second, we
suspect that selection will favour reduced dispersal by
myrmecophilous lycaenids, because of the difficulty associated
with locating patches that contain the appropriate combination
of food plants and ants. Thus, in addition to occurring as
isolated populations of variable sizes, ant-tended species may
express genetic traits associated with reduced outcrossing.
At this time, we cannot evaluate whether North American
lycaenids that associate with ants are more vulnerable to
endangerment or extinction than those without such
dependencies. This is because there have been almost no
studies of the ant associations of endangered lycaenid taxa.
However, Downey (1962) observed that the Mission Blue was
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tended by the ant Formica lasioides, and suggested (but did not
demonstrate) that ants may protect caterpillars from natural
enemies and even transport them to their food plants. D.A.
Savignano has studied the ant associations of the Karner Blue,
but this work has yet to be published.
Numerous studies of non-endangered taxa in North America
suggest that ants could be an important factor in the persistence
of lycaenid populations. For example, parasitism levels of
Glaucopsyche lygdamus oro (Scudder) (the Rocky Mountain
subspecific relative of the federally listed Palos Verdes Blue, G.
lygdamus palosverdesensis Perkins and Emmel) were 45–84%
lower for ant-tended larvae than for untended larvae (Pierce and
Mead 1981; Pierce and Easteal 1986). In Michigan, the work of
Webster and Nielson (1984) also suggested that ant associates
were beneficial for the Scrub-oak or Edward's Hairstreak,
Satyrium edwardsii (Grote & Robinson). Clearly, we need to
know much more about the ant associations of endangered
lycaenids, as these interactions will be important considerations
in management plans.
Although not from North America, the Large Blue
(Maculinea arion (L.)) provides an important, sobering, example
of the often dire consequences associated with a dependence on
ants (see Thomas 1980; Cottrell 1984; New 1991). Despite
considerable efforts to prevent its loss, in 1979 the Large Blue
became extinct in its native Britain. While many factors
undoubtedly contributed to this demise, the most prominent
appears to have been the species' extreme dependence on ants.
During early instars, M. arion larvae fed on wild thyme (Thymus
drucei praecox) and, at the fourth instar, were carried by
Myrmica ants into their nests, where the lycaenids fed on ant
brood. The level of grazing in the blue's grassland habitats was
progressively reduced from around 1950, largely due to changing
agricultural practices and attempts to protect habitat of this
endangered species. However, due to unforeseen complexities
of the system, these altered grazing regimes had drastic effects
on the lycaenid populations. The primary ant-species host (M.
sabuleti) could persist only in fields that were closely cropped
by livestock. Thus, even slight reductions in grazing allowed M.
scabrinodis, a low-quality host, to exclude M. sabuleti from the
area, thereby leading to the butterfly's subsequent demise.
Conservation planning in North America
Lycaenids have played a central role in the development of
environmental interests over land-use policy. Although much
less publicised than the Large Blue another lycaenid provides
a further example of the kind of conservation efforts that are
required to protect endangered butterflies.
The Mission Blue was conferred protection under the ESA
in 1976, when the U.S. Fish and Wildlife Service formally
recognized that encroaching urbanisation had virtually encircled
the known distribution of this subspecies. More than half of the
grassland habitat of the largest remaining known population on
California's San Bruno Mountain had been lost during the 50
years preceding the listing. Furthermore, half of this remaining
habitat (a quarter of the total) had been overtaken by invasive