Nest construction and larval behaviour of Bubas bison (L.) and Bubas bubalus (Ol.) (Coleoptera, Scarabaeidae)

Female beetles working alone or in cooperation with a male excavated vertical, tunnel‐shaped brood chambers. Each chamber was filled with dung to form a cylindrical brood mass which contained two eggs, one near each pole. To examine the possible relationship with other Onitini (which lay either one or several eggs per brood mass) factors that influence the two‐egg programme were studied. Brood masses with only a single egg were formed if excavation was resumed prematurely. Conversely, when excavation was suppressed several oviposition programmes fused to produce a multi‐egg brood mass. The larvae repaired their chambers in the typical Scarabaeine manner by building a self‐supporting wall formed from their own excrement. This behaviour also prevented direct contact and fighting between adjacent larvae in the same brood mass, and it allowed the larvae to survive inside artificial brood balls. Similar behaviour was observed in larvae of Onthophagus taurus and Onthophagus vacca (which develop in one‐egg brood masses). The evolution of nesting habits that involve multi‐egg brood masses or free‐standing brood balls may depend on the pre‐existence of this larval repair behaviour.