Multitrophic plant–insect–fungal interactions across 150 million years: A giant Agathoxylon tree, ancient wood-boring beetles and fungi from the Morrison Formation of NE Utah, and the brood of an extant orchard mason bee

Abstract

Although plant–insect interactions can be traced back to the Silurian, little is known from Upper Jurassic to mid-Cretaceous ecosystems. In the Upper Jurassic Morrison Formation, evidence is limited to insect body fossils and trace fossils in mostly wood. However, until now, multitrophic interactions have not been reported from the Morrison Formation. Here we describe a complex web of interrelationships between an ancient tree, fungi, and wood-boring insect from the Morrison Formation with an extant bee in NE Utah, USA, using microscopy, thin sectioning, and microCT for non-destructive internal imaging. The tree is Agathoxylon hoodii (Araucariaceae), one of the largest individuals in a monospecific forest, whose trunk was infected and decayed by white rot while the tree was alive during the Jurassic. Fungal formation of voids in the wood facilitated the boring of large-diameter galleries by an insect, likely a beetle. One gallery was repurposed by a modern orchard mason bee, Osmia lignaria, as a linear nest for her brood. The fossil wood specimen was serendipitously collected with two bee larvae plus food provisions in cocoons in the lowermost two chambers. Thus, this example is not only a simple interaction between fossil plants and insects, but transcends 150 million years between the ancient tree–insect–fungal relationship and a living insect.