Extensive management efforts are ongoing to address the post-Columbian expansion of several species of juniper in the western United States. The objective of this study was to improve our understanding of arthropod communities inhabiting the berry-like seed cones (hereafter, ‘berries’) of these invasive junipers, with particular interest in sources of seed mortality. This research builds on our previously reported findings from efforts focused exclusively on western juniper (Juniperus occidentalis) berry arthropod communities by investigating two additional species of juniper, Utah (J. osteosperma) and California juniper (J. californica), that are expanding their ranges in the western U.S. Utah juniper berries were collected from six locations in Nevada, and California juniper berries were collected from eight sites in California. Information regarding the identity and habits of most species occupying berries was revealed through rearings and berry dissections, along with DNA sequencing and traditional taxonomic efforts. Overall arthropod damage, along with damage associated with individual species, was assessed by dissecting 3399 berries from seven Utah juniper berry collection locations and 800 berries from five California locations.
Results/Conclusions
Arthropods have been encountered utilizing the berry skin, husk, resin glands, seed coat, and embryo. At each stage of berry development the seed, pulp and peel of the berries represent distinct microhabitats for arthropods, as well as their predators and parasitoids. Fourteen of the species found previously in western juniper berries were not collected from California or Utah juniper. Four of 41 species of arthropods collected from Utah juniper berries were not associated with the other two junipers, while 6 of 31 species from California juniper berries were unique to that host. Overall, 40.98% of Utah juniper berries were damaged by arthropods across five sites, while 18.13% of California juniper berries were damaged. The most frequently encountered seed destroying arthropods in Utah juniper were the wasp Eurytoma juniperina and Trisetacus sp. mites, and in California juniper were E. juniperina and several species of Lepidoptera. Reproduction of Juniperus spp., in the western U.S., is exclusively by seed. Increased knowledge of their arthropod seed predator communities is essential to understanding recent juniper range expansions. It also informs the search for candidate augmentative biological control agents and has revealed patterns of convergent evolution within specific berry niches of Juniperus spp., worldwide.