Oviposition and Oophagy by Workers in Queenright Colonies of Bombus (Pyrobombus) ardens (Hymenoptera, Apidae)

Oviposition and oophagy by workers in the queenright conditions were observed with four free-foraging colonies of Bombus (Pyrobombus) ardens SMITH. Worker oophagy started in late May to early June, namely soon after the beginning of worker oviposition which started about 20 days later than the start of laying of male-producing eggs by the queens. Worker oophagy never occurred during queen's oviposition processes. In colonies with higher worker oophagy, the queens frequently attacked workers around the new egg cells. Worker ovipositions in the queenright condition were observed more frequently in weak colonies than in populous colonies. The total number of eggs laid by workers was relatively small in each colony. Workers never attacked the queen during her oviposition processes. Aggressive behavior of laying workers was not intense in B. ardens and only an aggressive worker was observed in each colony. Aggressive workers never attacked the queens. This low and ephemeral worker aggressiveness may relate to the small colony size in B. ardens much lower than in other prolific species with higher aggressiveness and larger colony size as in B. ignitus SMITH.