Plant-insect interactions across geologic deep-time and modern ecosystems: Are insects hungrier in the modern?

Plant-insect interactions are fundamental to bottom-up ecosystem stability and may serve as indicators of instability. Plants and insects first formed relationships in the late Silurian-Early Devonian (417-403 Ma) but these ancient relationships are shifting with anthropogenic change. Previous work has linked leaf litter to standing forest diversity and insect herbivory to insect diversity; however, linking these studies to the fossil record is challenging due to differing methodologies. Here we compare the frequency of herbivory and the diversity of damage morphologies observed on angiosperm leaf compression fossils from the Cretaceous-Pleistocene (66.8-2.06 Ma; 58 sites) to two modern temperate ecosystems, Harvard Forest (MA) and the Smithsonian Environmental Research Center (MD), and one modern wet tropical ecosystem, La Selva, Costa Rica. Modern ecosystems were sampled to mimic paleobotanical sampling methods. We found that frequency of modern insect herbivory is significantly higher than the geologic record and several functional feeding groups show higher diversity, as well. This change in modern herbivory can be linked to anthropogenic climate change along with other human disturbances such as land fragmentation and introduction of invasive species. The introduction of Lymantria dispar is evident in Harvard Forest with significant surface feeding, likely created by L. dispar caterpillars. As anthropogenic climate changeand human influence are altering the diversity and abundance of modern insect groups, these results are surprising and further research is needed to better understand why insect feeding is considerably higher in the modern era, even as insects decline.