PLANT-INSECT INTERACTIONS IN THE MIDDLE MIOCENE OF NEVADA

Middle Miocene deposits from the Savage Canyon and Buffalo Canyon Formations of Nevada, provide a unique opportunity to examine plant-insect interactions in deposits of similar age, depositional environment and geographic location. These formations also preserve similar taxa. Fossil-bearing strata from within these two lacustrine deposits are approximately 50 km apart. We examined fossil leaves from these formations to assess whether plant-insect interactions were more influenced by large scale, regional factors or by fine-scale, local factors such as microclimate and/or community structure. If large-scale factors are more important, then similar patterns of insect-feeding damage should be present in both formations.

In this study we focused on leaves of Salicaceae, Fagaceae and Rosaceae, as these families are found in high abundance in both formations, and have high quality preservation. We examined 643 leaves from the Buffalo Canyon Formation and 465 leaves from the Savage Canyon Formation, and recorded the number of each of the following damage types found on each fossil leaf: hole feeding, skeletonizing, margin feeding, galling and leaf mining. Leaf damage was much higher for Buffalo Canyon (51%) than for Savage Canyon (34%), with hole-feeding being the dominant damage type in both assemblages. Although a few examples of specialized feeding damage can be found on the same leaf taxa from both assemblages, it appears that local factors are more important in determining insect feeding patterns on plants. This is also consistent with studies of modern forests, where subtle differences in microhabitat can result in large differences in insect damage levels. Future work will examine the spatial distribution of damage patterns within each of the Miocene deposits, and comparisons will be made to patterns of damage found on modern members of these plant families.