Brood cells, life-cycle stages and development of some earth-borer beetles in the generaBolborhachium, BlackburniumandBolboleaus(Coleoptera: Geotrupidae), with notes on captive rearing and a discussion of larval diet

Abstract

Studies in Western Australia have revealed new information on the natural history of beetles in the genera Blackburnium, Bolboleaus and Bolborhachium (Bolboceratinae), all of which are notable for their relatively enormous eggs. Most of the information concerns Bolborhachium recticorne (Guérin-Méneville 1838), which was studied at a perennial nesting site. This species (with two exceptions), and some congeners, constructed built-in brood cells using transported surface soil. By contrast, Blackburnium reichei (Guérin-Méneville 1838) and Bolboleaus hiaticollis Howden 1985 excavated simple chambers for their eggs. Egg to adult development in all species occurred in the brood cells. Eggs and larvae collected in the field were reared in their original cells and in artificial cells made in soil. Of three instars, the first contained the already developed second instar and did not feed. Second and third instars nibbled at the walls of their cells as if feeding, grew in size and increased their weight 2.5–3.0 times. However, they turned over little soil, ingested little solid material and rarely passed faeces, so ingestion and digestion of ‘humus’ (finely divided plant detritus) is unlikely to account for all (if any) of their weight gain. As the contents of the larval intestine were hygroscopic, perhaps larvae ingest salts and/or humic and fulvic acids that enable them to absorb water. Soil bacteria are suggested as a source of nutrition for the larvae.