Mitoura loki thornei

Thorne's Hairstreak

Mitoura loki thornei is known only from the Otay Mountains Wilderness near the Mexican border, where it flies among stands of its host Tecate Cypress (Cupressus forbesii) - a rare butterfly dependent on an uncommon tree.

Thornei has two broods, the first with adults flying late February through March, and the next in June/July. The early brood emerges from over-wintered pupae. Females oviposit on new growth on mature trees, and larvae emerge a week or two later and bore into young stems during the first instar (later instars feed on the outside of the plant). After 26-35 days developing as larvae, they pupate for 10-15 days in the ground litter at the base of the host. This summer brood then emerges to mate and their offspring overwinter as pupae, and the cycle begins anew. [Source] According to Michael Klein, a biologist who knows this species exceptionally well, wet season forms may have green underneath; dry season forms are more brownish/purple.

Thorne's Hairstreak
Thorne's Hairstreak from Otay Mesa, March 8, 2008. They can be found pretty easily by searching the host cypresses along the road.
Thorne's Hairstreak
Another Mitoura loki thornei from the same day.
Tecate cypress from Otay Mountain
Cupressus forbesii - Tecate cypress - is restricted to a few places in the U.S. and Mexico. Infrequent fires benefit this tree and thus the butterfly. Seeds are dispersed from cones opened by fires. But the larger fires we're experiencing now - such as the 2003 Mine Fire - have put the butterfly in peril as they threaten to wipe out entire groves of the mature trees the butterfly prefers.
Thorne's Hairstreak
I found a few more thornei on a March 20, 2010 day-trip to Otay Mountain.

©Dennis Walker