INSECT FLUID-FEEDING ON UPPER PENNSYLVANIAN TREE FERNS (PALAEODICTYOPTERA, MARATTIALES) AND THE EARLY HISTORY OF THE PIERCING-AND-SUCKING FUNCTIONAL FEEDING GROUP

We document the presence of the piercing-and-sucking functional feedin g group and the dietary targeting of vascular tissue (phloem and xylem ) in marattialean tree-fern rhachises from a Late Pennsylvanian (302 M a) coal-swamp for est in the Illinois Basin. Our evidence originates f rom per mineralized peat that exhibits cellular-level preservation of tissues from whole Psaronius tree-fern rhachises; it includes 3 stylet probes, each of which traverses epidermal tissues and parenchyma, and terminates in a distinctive feeding cavity within phloem and xylem of a vascular strand. The styler probes are lined with an opaque, sheath like material, and are principally intracellular, although large gum s ac cells are avoided. One of their most diagnostic features is 1 or 2 ridges occurring on the inner surface of each stylet probe, parallelin g most of the probe length. These ridges, documented by light and scan ning electron microscopy, are interpreted as host tissue casts of inte rstyletal sulci. From these and other features of stylet-trace morphol ogy, we conclude that the herbivore was an insect of the order Palaeod ictyoptera rather than an hemipteroid insect. Well developed reaction tissue surrounding the styler trace developed while the plant host was alive, demonstrating herbivory. Precious studies have documented pier cing-and-sucking in several examples of plant damage from the Early De vonian to Late Pennsylvanian (395-290 Ma). The oldest crebible example s are plant lesions indicating piercing-and-sucking arthropods from 2 Lower Devonian deposits. We hypothesize that in later Middle Pennsylva nian, equatorial, coal-swamp forests of Euramerica, the dominant arbor escent plants possessed vascular tissues largely unavailable to insect s, because they were either deeply embedded in thick cortical tissues or protected by outer indurated, peridermal tissues. Subsequent tree-f ern forests of the Late Pennsylvanian provided accessible vascular and other tissues to surface-dwelling insects with stylate mouthparts-a c ondition which continued into the Permian and propelled the hemipteroi d radiation.