Type: report

Article abstract: This report covers activities performed during our third year of work with Thorne's hairstreak (TH). Activities are summarized with reference to objectives as outlined in our second annual report, and activities for 2013 are projected (the project will come to an end mid- 2013). During the 2011 field season, we completed our surveys for vegetation and TH abundance. Over the course of both of our primary field seasons for this project (in 2010 and 2011), we surveyed a total of 358 plots for vegetation and 255 plots for TH presence and abundance associated with 40 stands of Tecate cypress. A total of 75 TH adults were observed in approximately half of the stands spread throughout the Otay Mountain study area. We also report here on results from habitat modeling, which suggests that host plant variables (e.g. cypress density and tree diameter) are statistically significant predictors of TH presence (while the density and richness of some potential nectar sources, for example, are not). These models, however, explain relatively little of the variation in TH observations, which we interpret in light of TH presence throughout the study area. In addition to observational studies, we were successful during the 2011 field season in carrying out experiments with TH larvae: 86 larvae were exposed to Tecate cypress foliage collected from trees that were either young, of medium age, or relatively old. Contrary to previous reports involving TH, but consistent with other work in the genus Mitoura, younger foliage was a superior larval resource. Future work would be needed to draw inferences regarding consequences for adult fitness in the wild. In summary, most tasks have been completed, and most objectives have been met for this project, including the experiment with caterpillars, which was previously uncertain given the sporadic availability of females.