Boisduval's Blue 

Plebejus icarioides (Boisduval) 


Yaeger Mesa, Orange County, CA (Charles Slater, Sandra and Ron Huwe)

Lepidoptera: Lycaenidae

© Peter J. Bryant.
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© Charles Slater

Characteristics: At first glance, males closely resemble those of the Southern Blue (Glaucopsvche lygdamus australis). The ventral hind wing, however, is nearly devoid of spots, nearly always present on the ventral hind wing of the Southern Blue. The female has brown and some blue scaling on the dorsal wing surface, with brown marginal markings.

Habitats, Behavior: The Trabuco Blue is almost always found associated with the presumed larval foodplant, Bush Lupine (Lupinus excubitus variety hallii). It has also been seen near streams, taking up required nutrients and/or water from the damp sand or mud.

Distribution: The "Trabuco Blue" is currently known from several locations in Trabuco Canyon and was first taken in Holy Jim Canyon at elevations ranging from 1800 to 3000 feet. Ron Vanderhoff has taken specimens of the Trabuco Blue in a side canyon of Silverado Canyon. A closely-related population is located on the northwest slope of Santiago Peak at an elevation of 5000 feet, but specimens from there have much darker VHW markings.

Flight Period: The Santa Ana Mountains populations are known to fly from late April into the middle of June.

Larval Foodplant: The "Trabuco Blue" has thus far only been found in association with Bush Lupine (Lupinus excubitus var. hallii), and this is almost certainly the larval foodplant.

Other Remarks: These unique populations were first brought to my attention through two specimens in the collection of Theodore Hower, captured in June, 1930 in Holy Jim Canyon. In 1974, Charles Sexton located a colony at Yaeger Mesa and other populations have since been located in the Santa Ana Mountains of Orange County. A colony on Lupinus excubitus  was found at Yaeger Mesa on May 7, 1999 by Charles Slater, Sandra and Ron Huwe. 

The species itself (Plebejus icarioides) is found throughout the western states. The subspecies evius is generally distributed throughout the montane areas of southern California, usually at intermediate elevations, and almost always closely associated with a lupine foodplant. The "Trabuco Blue", differs from true evius by the general lack of black spots on the VHW surface. In addition, this unique butterfly inhabits elevations much lower than true evius.

Although the "Trabuco Blue" does differ from the southern California subspecies evius, the Trabuco and Silverado Canyon icarioides populations probably do not warrant a distinct subspecific name. Downey (in Howe, 1975) has questioned the validity of some subspecies of icarioides after experiments in which individuals reared in environmental conditions not typical of their normal habitat, exhibited abnormal wing patterns typical of other named subspecies from other areas. An enterprising lepidopterist familiar with rearing techniques could shed much light on this interesting subject by confining fertile females of the "Trabuco Blue", collecting eggs, and rearing the resultant larvae in temperature and humidity conditions different than what occurs in the native habitat. The adults thus reared could be compared with specimens of icarioides evius in order to determine if they still resemble typical Santa Ana Mountain specimens or perhaps possess the heavier maculation on the ventral surfaces typical of icarioides evius.

The biggest problem in rearing icarioides at this time, however, is the problem of obligatory larval diapause; the species in nature overwinters in the larval stage. Many larvae die in the laboratory during this period, and artificial means for breaking diapause in this species have not been totally successful. In nature, diapause extends through the summer, fall, and winter months for this butterfly.

From Orsak, L. J. (1977). The Butterflies of Orange County, California. Center for Pathobiology Miscellaneous Publication #3. University of California Press, New York. 349pp. with updates by Peter Bryant.

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