Beetle borings in wood with host response in early Permian conifers from Germany

Wood boring represents a common feeding and survival strategy in several lineages of beetles. The larvae of wood-boring beetles hatch and excavate tunnels in wood during their development. The origin and evolutionary history of this life habit, however, remain poorly understood to date, as the fossil record is scarce. We present new silicified conifer wood specimens containing complex borings from the lowermost Permian Manebach Formation of the Thuringian Forest Basin in central Germany and the lower Permian Donnersberg Formation of the Saar–Nahe Basin in southwestern Germany. Additionally, this distinctive type of wood boring is recorded from the Carboniferous/Permian of the Czech Republic, Poland and China. For these borings, the new fodinichnion or agrichnion Pectichnus multicylindricus igen. et isp. nov. is established. It is characterised by several parallel cylindrical tunnels in a longitudinal arrangement, branching from a tangential primary tunnel oriented perpendicularly. The borings contain frass as coprolites made up of undigested wood cells. The conifer trees responded to the borings with callus production that subsequently filled or enclosed the tunnels. This is the earliest record of this specific life habit of ancient insects. The novel wood-boring strategy required structural modification and physiological adaptation; it probably emerged when insect diversity expanded considerably as terrestrial environments changed dramatically.