FOSSIL EVIDENCE OF LATEX SABOTAGING BEHAVIOR BY HERBIVOROUS INSECTS

Plants, insects, and their ecological interactions have been key components of global terrestrial ecosystems throughout geologic time. The arms race between latex-producing plants and latex-sabotaging insect herbivores—resulting in increasingly deadly latex in plants and progressively complex sabotaging behaviors in insects—is one such ecological interaction known to be important in modern ecosystems. However, although latex has been identified in the fossil record, ancient latex-sabotaging behavior has not previously been described. Here we report on the discovery of four fossil leaves from the middle Eocene Geiseltal brown coals in Germany (approximately 45 million years old) preserved with branched laticifer systems and damage indicative of latex-sabotaging insect behavior. Two types of damage are evident on compressions of dicot leaves. One fossil leaf shows repeated, regularly spaced vein cuts along the midrib, while three other leaves show continuous trenching across the leaf lamina. These damage patterns are recognized as pertaining to previously described Damage Types for repeated hole feeding on the leaf midrib, DT50, and for the narrow, trenched feeding of the leaf lamina, DT198, although they had not been associated with latex-bearing structures in previous work. It is specifically the co-occurrence of these damage types and the branched laticiferous system in the Geiseltal leaves described here that point to latex-sabotaging insect behavior. The middle Eocene age of the Geiseltal leaves with these types of insect damage is likely close to that of the origins of latex among flowering plants, suggesting a rapid evolutionary response by insect herbivores.