Do changes in levels of insect damage correspond to changes in climate? What climatic variables are the best predictors of insect damage on plants? To learn more about how climate influenced ancient interactions between plants and insects, we examined two fossil floras from the Middle Miocene of Nevada. The Buffalo Canyon (15.5Ma) and the Savage Canyon (14.1Ma) Formations have the same or closely related plant groups, including many modern species.

In this study, we focused on the fossil leaves of Salicaceae, Fagaceae and Rosaceae, as these families had the best preservation, including traces of insect damage that are easily discernable, and highest abundance of leaves in the fossil sites. In addition, these families are known to have host-specific interactions with modern herbivores. We examined 310 leaves from the Buffalo Canyon flora and 438 leaves from the Savage Canyon flora. We documented amounts and types of damage on the fossil leaves including; number of leaves damaged, number of damage types found on individual leaves, and whether leaves had evidence of specialized, host-specific damage.

Damage levels were significantly higher (x2=158.95, P<0.0001) in the Buffalo Canyon flora. The majority of leaves in both fossil assemblages had only one type of insect damage, and this damage was usually created by external foliage feeding insects. We did find evidence of specialized, host-specific damage on some of the same species of plants at both sites. Of the climate variables examined, we found that precipitation was the best predictor of overall damage levels.