Preference and performance of juniper hairstreak (Callophyrs gryneus) in expanding Juniper woodlands of the Intermountain West

Abundant evidence indicates that Juniper woodlands in the Intermountain West have expanded in extent and canopy cover, and have undergone substantial changes in forest age structure over the last 150 years. Woodlands are now dominated by an abundance of young, immature, early expanding trees, however, little is known about community consequences resulting from a changing forest age structure, despite the fact that these differences are important to include in long-term management planning. Using the Juniper Hairstreak (Callophyrs gryneus), we investigated the preference and performance of the specilaist herbivore on foliage from young, early expanding Juniper trees and mature, old-growth Juniper foliage. We used two currently expanding Juniper species in the Intermountain West, Juniperus osteosperma and J. occidentalis, and compared the results. We also identified and quantified the differences in secondary metabolites within the plant tissue of immautre and old-growth foliage using spectroscopic techniques. The results indicate that the specialist herbivore preference varies between populations, but overall females prefer to lay eggs on old-growth foliage. However, the larvae grew more slowly and had smaller pupal weights when fed foliage from old-growth foliage, suggesting a mis-match between the preference and performance of this specialist herbivore. Finally, we found that the chemical profile of the foliage from immature and mature trees differed in concentrations of a few select compounds and differences also existed between the two juniper species. These results suggest that the changing forest age structure could have cascading effects to higher trophic levels and alter community structure in a widespread, specialized desert community.