Nest defense and early production of the major workers in the dimorphic ant Colobopsis nipponicus (Wheeler) (Hymenoptera : Formicidae)

Summary Production of the major subcaste and its contribution to nest survival in the dimorphic ant Colobopsis nipponicus was examined in the field. In this species, the first major workers were reared in the second brood, very early in the colony life cycle. A field experiment demonstrated that artificial colonies without major workers could not survive, whereas colonies with at least one major worker per nest entrance could. Because major workers of C. nipponicus defend the nest entrance by head plugging, the lack of nest defenders in the experimental colonies seemed to be a major cause of nest failure. The defensive value of major workers was much higher than that of minor workers. Many artificial colonies without major workers were displaced by competitors for nest sites, especially by those of other conspecific colonies. In addition, more than 90% of field colonies nested with other conspecific colonies on the same tree. The early production of major workers in C. nipponicus seemed to be very important for the survival of incipient colonies.