Distribution of foundress group size in Ropalidia fasciata and R. plebeiana (Hymenoptera: Vespidae): an analysis using zero-truncated distribution models

Abstract

Distribution patterns of the number of foundresses per newly established nest (foundress group size, FGS) of two primitively eusocial, independent-founding wasps, Ropalidia fasciata and R. plebeiana, were studied using zero-truncated distribution models. The distribution pattern of the FGS of R. fasciata is significantly different from a zero-truncated Poisson distribution but fits the zero-truncated negative binomial distribution well, indicating a strongly contagious distribution. R. plebeiana sometimes establishes new colonies by reusing old nests. In this case, distributions are strongly contagious. Competition among foundresses may be one reason for the contagious distribution of FGS in R. fasciata and in cases of old-nest reuse by R. plebeiana, but further studies, especially on the behaviour of foundresses in relation to FGS, are necessary.