Palos Verdes Blue
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| Glaucopsyche lygdamus palosverdesensis |
The Palos Verdes Blue butterfly is a small endangered butterfly native to the Palos Verdes Peninsula in southwest Los Angeles County, California. As its distribution has been proven to be limited to one single site it has one of the best claims to being the world's rarest butterfly.
Palos Verdes Blue (G. lygdamus palosverdesensis) is a localized subspecies of silvery blue (G. lygdamus). It was described in 1977, shortly before it became one of the second groups of butterflies to be listed under the US Endangered Species Act in 1980 (Mattoni 1995). It is distinguished from other subspecies of G. lygdamus by its slightly different patterning on the underside of the wing, an earlier flight period, and use of a locoweed (Astragalus trichopodus) as a larval food plant (Mattoni 1995). The distribution of the subspecies as described was the southern slope of the Palos Verdes Peninsula in coastal Los Angeles County.
The Palos Verdes blue butterfly was thought to be driven to extinction in 1983 by development of its habitat (Mattoni 1995). Then, in 1994, the butterfly was rediscovered by Rick Rogers, Rudy Mattoni, and Timothy Dahlum at the Defense Fuel Support Point in San Pedro, which is located on the northern (inland) side of the Palos Verdes Peninsula. This new population lays eggs on a different foodplant (common deerweed, Lotus scoparius) but shares physical and behavioral characteristics with the other now-extinct populations.
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[edit] Biology of Palos Verdes blue (PVB)
[edit] Taxonomy and systematics
PVB, Glaucopsyche lygdamus palosverdesensis, is a subspecies of the G. lygdamus (Silvery Blue) species of butterfly found throughout North America. There are currently 11 subspecies of silvery blue. G. lygdamus palosverdesensis was first described in the 1970s and was distinguished from other G. lygdamus by its faster and early flight, wing color and wing spot patterns (Lipman 1999).
[edit] Morphology
This butterfly has a wingspan of only 25-30 mm. The male has a bright silvery-blue dorsal wing outlined in a narrow line of black, while the female’s dorsal wing is a more brownish-gray color. Both males and females have gray ventral wings with dark spots surrounded by white rings (Arnold 1987).
[edit] Habitat
G. lygdamus palosverdesensis persists particularly on the Palos Verdes Peninsula, 15 miles south of Los Angeles, in a coastal sage scrub habitat. This species is locally monophagous, or particular to one species of foodplant. The entire species was originally thought to be particular only to the locoweed or rattlepod Astragalus trichopodus lonchus, but the population rediscovered in 1994 used Lotus scoparius (common deerweed) as its larval foodplant (Lipman 1999). These two types of plants are fast becoming scarce on the Palos Verdes peninsula because of housing development. Retention of these larval foodplants is essential for conservation of the Palos Verdes blue.
[edit] Life Stages
Oviposition, laying of eggs on the larval foodplant, occurs only once a breeding season for PVB. There are at least 4 larval instars, or stages of development. After 7 to 10 days the larvae emerge and crawl to the base of the foodplant where they pupate. Pupae remain in diapause until emerging as adults (Lipman 1999). The flight period and reproductive period occur together for PVB, beginning in late January and ending in early May. It is rare to see PVB far from its home food patch, but research shows that males cover more distance and have longer periods of flight (Lipman 1999). Palos Verdes blue are a diurnal and panmictic species. They are also non-migratory and very particular in their use of larval foodplants. The PVB adult lifespan is only five days (Isbell 1996).
[edit] Relationships with other species
Interspecific competition may occur with other lycaenid butterflies for the larval foodplant. A mutualism between ants and larvae has been observed during the instars of butterfly development. G. l. palosverdesensis has a host-parasite relationship with its larval foodplants, Astragalus lonchus and Lotus scoparius. There has also been observed predation on Palos Verdes blue by Western Yellowjackets (Vespula pennsylvanica) at the Defense Fuel Point location (Lipman 1999).
[edit] Conservation
[edit] Laws
G. lygdamus palosverdesensis was listed as an "endangered species" by the Fish and Wildlife Service on July 2, 1980. This listing also included city-owned Critical Habitat, plus comments and recommendations for species conservation. Insects are not currently protected by California law.
[edit] Threats
The main threat to the Palos Verdes blue has been habitat destruction due to weeds and rototilling, which has negative effects on the essential larval foodplants. Recreational, commercial, or residential development of the Palos Verdes peninsula is also a major concern in preservation of the foodplants (Greenwalt 1980).
[edit] Reintroduction
The Palos Verdes peninsula is split into the north and south slopes. On the north slope, reintroduction is suggested based on presence of deerweed (Lotus scoparius) and a native plant index number. The only habitat known so far on the north slope is the Defense Fuel Support Point location. The south slope has many more historic sites of Palos Verdes blue, which are all suggested for reintroduction, including any more sites containing locoweed (Astagalus) (Lipman et al. 1999). Particular sites of reintroduction and rehabilitation of the PVB include Defense Fuel Support Point in San Pedro and the Linden H. Chandler Preserve (Lipman et al. 1999).
[edit] Mass rearing
Mass rearing of PVB has been taking place since rediscovery in 1994. The mass rearing is conducted for conservation purposes, reintroduction and prevention of extinction. The mass rearing takes place in “tent” cages containing both known larval foodplants (Mattoni et. al 2003). It has been variably successful.
[edit] Modeling
Although Population Viability Analysis (PVA) models are often very important for predicting the outcome of conservation efforts, there have been many problems with using PVA models to predict Palos Verdes blue populations. This type of modeling has proved inconclusive mainly because the PVB utilize habitat so variably, depending on climatic and succesional changes (Lipman et al. 1999). So far, the appropriate habitat has been hard to find, and expert intuition has often been wrong. Metapopulation modeling would seem like an appropriate choice for the Palos Verdes blue, but there is a lack of demographic and genetic information. Long-term population studies are not available to provide this information because of the many local extinctions and declining numbers of this species (Lipman et al. 1999). For this reason, PVB long-term viability is very difficult to predict.
[edit] Key Conservationists
Rudi Mattoni is a biologist at the University of California, Los Angeles who has been instrumental in research on Palos Verdes blue, particularly with the program at Defense Fuel Support Point in San Pedro. Richard Arnold has also researched and written about PVB. The Youth Environmental Service program of the Palos Verdes / South Bay Audubon Society has provided help weeding and establishing habitat for the butterfly.
[edit] References
- Arnold, R.A. 1987. Decline of the Endangered Palos Verdes Blue Butterfly in California. Biological Conservation. 40: 203-217.
- Greenwalt, L.A. 1980. Listing the Palos Verdes Blue butterfly as an Endangered Species with Critical Habitat. Federal Register. Fish and Wildlife Service, Interior. 45 (129): 44939-42.
- Isbell, C.M. 1996. Green Teens Save the Blues. Audubon. 98 (5): 102-105.
- Lipman, Alison; Longcore, Travis; Mattoni, Rudi & Zhang, YinLan. 1999. Habitat Evaluation and Reintroduction Planning for the Endangered Palos Verdes Blue Butterfly. Final Technical Report to California Department of Fish and Game. 1-47.
- Mattoni, R., Longcore, Travis; Krenova, Zdenka & Lipman, Alison. 2003. Mass Rearing the endangered Palos Verdes blue butterfly (Glaucopsyche lygdamus palosverdesensis: Lycaenidae). Journal of Research on the Lepidoptera. 37: 55-67.
- Mattoni, R. 1992. Rediscovery of the Palos Verdes endangered blue butterfly, Glaucopsyche lygdamus palosverdesensis Perkins and Emmel (Lycaenidae). Journal of Research on the Lepidoptera. 31 (3-4): 180-194.
