MAJOR PROCESSES IN THE DEVELOPMENT OF ARTHROPOD HERBIVORY ON LAND

The history of insect herbivory on land is divided into six events that describe the expansion of herbivores onto vegetated landscapes. This history is connected to processes that include the colonization of plant taxa by insect herbivores, herbivore partitioning of plants based on their tissue types, development of herbivore component communities, and the diversification of plant and their insect herbivore lineages. The first major event was the initial colonization of the land flora during the Late Silurian, ending in the Late Mississippian. This process includes evidence for herbivory in the Middle Devonian and the appearance of margin feeding by Late Mississippian, and is associated with highly variable lags between the first appearances of plant organs and tissues and their initial herbivorization. The second event was development and consolidation of the earliest component herbivore communities on a single source plant, providing a feeding matrix of generalists and specialists. By Late Pennsylvanian, this process is well established for Psaronius tree ferns in Euramerican coal swamps and nearby habitats, and included a near-complete repertoire of herbivore feeding groups that are recognizable today. A third major process was the second expansion of herbivory in dryer, mineral-substrated habitats, resulting in an expansion of ovipositing, galling, and piercer-and-sucking insect lineages on diverse Euramerican plants and Glossopteris in Gondwana. After the end-Permian ecological crisis and clearing of much of landscape vegetation, there was a fourth process involving the great expansion of herbivory, principally on emerging and diverse gymnosperms. Following this protracted process is the fifth process, the mid-Cretaceous diversification of angiosperms that provided ecological opportunities for arthropod herbivores, most which were repeat associations on earlier gymnosperms. The end-Cretaceous extirpation of many plant–insect associations had major, immediate and negative consequences during the Paleocene, dwarfed by the end-Permian event. There was a subsequent expansion of insect herbivory during the remaining Paleogene that was disrupted by the sixth major process, the Neogene expansion of grasslands, savannas and their insect herbivores.