BURROWING TECHNIQUES, BEHAVIORS, AND TRACE MORPHOLOGIES OF EXTANT LARVAL TO ADULT BEETLES

Studies of the relationships between extant tracemakers, environmental conditions, and trace morphology allow for the interpretation of ichnofossils. Despite being abundant, prolific burrowers today, beetles (Coleoptera) have a relatively poorly understood trace-fossil record. This study examined the behavior and trace morphology of three extant beetles, Tenebrio molitor, Zophobas morio, and Phyllophaga sp., from their larval to adult life stages under normal and stressed environmental conditions in a laboratory setting. Tests were used to determine the burrowing techniques, behaviors, and trace morphologies of each species under natural conditions, how behaviors and burrow morphologies changed when sediment composition, moisture, and compaction were altered, and the ichnofabric index (ii) produced throughout the life cycle of 12-24 specimens in 10, 20, and 56-gallon terraria. Tenebrio molitor and Z. morio used similar compression and intrusion burrowing techniques using their entire head and distal spine. Tenebrio molitor were mostly near-surface vagile burrowers, while Z. morio was a sporadic vagile burrower that inhabited all depths but favored deep tiers when constructing their pupation chambers. Tenebrio molitor and Z. morio larvae produced open, straight to sinuous, shafts and tunnels with compression linings, false branching, and some evidence of maintenance from tunnel reuse producing an ii of 4-5. Phyllophaga were vagile burrowers that utilized excavation and backfilling burrowing techniques using their entire head, limbs, and dorsal abdomen. They occupied more varied depths including deep tiers, but favored the near surface in dry and sandy substrate. Phyllophaga larvae created burrows consisting of series of small, ellipsoid-shaped, backfilled packets that were non-branching, straight to sinuous with some sharp turns, and an ii of 1-3. The larvae occupied mobile ellipsoid chambers where they fed on organic material. All three species created ellipsoid pupation chambers with an average width to height ratio of 1.46-2.12. Neoichnological studies improve our understanding of extant soil animal traces which can aid in recognizing their ichnofossils when body fossils are not present, improving interpretations of paleoecosystems and paleoenvironments in continental settings.