Current Distribution Rangewide

Endemic to San Diego County and occurs exclusively in the vicinity of Otay Mountain, confined to areas where Tecate cypress grows [1].

Known Populations in San Diego County

Within the MSPA, Thorne’s hairstreak is found in MU 3 [2].

List Status

Not listed

Habitat Affinities

Occurs in chaparral ecosystems in southern California and northern Baja California. Dependent on its larval host plant, Tecate cypress (Hesperocyparis forbesii), a closed-coned conifer that occurs on mesic slopes and drainages in chaparral [3]. Tecate Cypress is also an imperiled species [4].

Taxonomy and Genetics

A small butterfly of the family Lycaenidae (Gossamer-wings) and subfamily Theclinae (hairstreaks) [3]. The taxonomic placement of Thorne’s hairstreak has been a topic of debate between species experts for several years. Recently, the taxonomy has changed from Mitoura thornei to Callophrys thornei [5].

Seasonal Activity

Bivoltine (producing two broods per season); first generation emergence in late February through March and possibly early April, depending on winter rainfall [6]. The second generation emerges in late May to early June. The species overwinters in the pupa stage within leaf-litter under trees.

Life History/Reproduction

Females oviposit eggs on newly established Tecate cypress host plants and incubate for 7 to 14 days [3]. Newly hatched larvae closely resemble the terminal twigs they feed upon. Complete larval development usually lasts 26- 35 days. First generation emergence occurs in late February through March. Second generation emergence occurs in June through July [3].

Diet and Foraging

Monophagous during the larval stage and dependent on Tecate cypress for its survival [1]. First generation adults have been observed using Ramona lilac and deerweed. Second generation adults were observed using California and flat-topped buckwheat only [6].

Dispersal

Dispersal behavior is not well known. The species’ small range on Otay Mountain suggests significant limits in dispersal [3]. On Otay Mountain it is confined to places where the larval foodplant, Tecate cypress grows. Although a significant stand of Tecate cypress occurs to the north in Coal Canyon, Orange County, California, and small populations are found to the south in northwestern Baja California, Mexico, Thorne's Hairstreak has not been documented to occur in those localities [7].

Threats

Mainly threatened by frequent wildfires, habitat destruction, and global climate change [1, 8]. In the long term infrequent fires are essential to maintain populations of Tecate cypress which enables seed dispersal. [9, 10]

Special Considerations:

In 2003 and 2007, wildfires swept through Otay Mountain impacting both Tecate cypress and butterfly [6]. Cypress experts began to analyze the effects of these large scale fires and gathered to discuss at a symposium in June 2010. The overall conclusion was that even with continuous fires, Tecate cypress will not likely become extirpated. Based on recent research Thorne’s recovery appears to be stable [6].

Literature Sources