NEOICHNOLOGICAL STUDY OF BURROWING DARKLING BEETLES (COLEOPTERA: TENEBRIONIDAE) FROM LARVAL TO ADULT STAGES

Beetles (Coleoptera) are a diverse group of insects that are a critical component of terrestrial ecosystems filling numerous ecological roles. Soil-dwelling beetles produce distinct biogenic structures in their larval, pupal, and adult stages and play an important role in soil development. Tenebrionidae (darkling beetles) is a common, globally distributed group that includes many soil-dwelling species from a variety of environments. However, little is known about the traces produced by these beetles.

The purpose of this project was to gain a better understanding of biogenic structures produced during each life stage of two species of darkling beetles, Zophobas morio and Tenebrio molitor. Single to multiple specimens of each species were placed in three sizes (6 L, 14 L, 38 L) of sediment-filled enclosures. The sediment included either massive, organic-rich loam with and without layers of food (apples) or alternating layers of organic-rich and organic-poor loam with and without layers of food. The sediment was kept moist and temperature maintained at ~22°C.

Biogenic structures were described and compared based on changes in life stage, species, sediment composition, food availability, and space availability. Biogenic structures were distinct between each life stage and associated with different behaviors. Within each life stage, biogenic structures were similar between each species, although Z. morio produced a greater abundance of traces in their larval stage. Observed larval traces included open, sinuous, horizontal to vertical burrows with false to simultaneous branching. Pupal traces were ovoid, open chambers with a greater width than height. Adult traces included actively to passively filled shafts from the pupal chambers and surface indentations. Observed biogenic structures are comparable to Palaeophycus, Fictovichnus, and Conichnus.

Neoichnological studies such as this can aid in the understanding of biogenic structures in the fossil record. Soil beetle abundance is high in both modern and ancient ecosystems, but their body fossils are relatively rare. Given their life habits, beetle trace fossils should be abundant. Being able to effectively link continental traces to tracemakers will ultimately improve our understanding of the composition of ancient terrestrial ecosystems.