A Triassic tritrophic triad documents an early food-web cascade

Abstract

Endophytic oviposition behavior, the insertion of eggs into plant tissues, represents a sophisticated reproductive strategy of insects.1 This process is accomplished by employing a specialized egg-laying device, the ovipositor, that effectively protects eggs through plant tissue concealment.2,3 Endophytic oviposition behavior is currently common in many lineages of several major, extant insect orders, principally Odonata (dragonflies and damselflies), Orthoptera (katydids and grasshoppers), Hemiptera (cicadas, aphids, scale insects, whiteflies, leafhoppers, and bugs), Coleoptera (beetles), Lepidoptera (moths), and Hymenoptera (sawflies).3,4 Based on the occurrences of egg insertion damage and associated scar tissue expressed in fossil plant stems and leaves, endophytic ovipositional behavior is presumed to have emerged as early as the Early Pennsylvanian Period.5 However, for impression fossils, egg morphology and surrounding scar tissue can be difficult to discern on plants, often resulting in ovipositional damage that may be assigned to exophytic (eggs laid on plant surfaces) or to endophytic behavior.6,7,8,9 This ambiguity is due to the spatial relationships and histological mingling of ovipositional damage and enveloping scars with adjoining plant-host tissues. Here, we describe body fossils of insect eggs within ginkgophyte leaves from the Upper Triassic of China. Feeding damage from an egg-predatory insect commonly occurs on these eggs, as some eggs bear up to several feeding punctures. We provide exceptional body-fossil evidence for resource use of a host plant by an ovipositing insect and unravel the earliest-known tritrophic cascade of a host plant, an ovipositing insect, and an egg-predatory insect.