Demography of the Okinawan eusocial wasp Ropalidia fasciata (Hymenoptera: Vespidae) II. Effects of foundress group size on survival rates of colonies and foundresses, and production of progeny
2008
ITÔ, Yosiaki | ITIOKA, Takao
Using demography data for the primitively eusocial wasp Ropalidia fasciata collected at 10 survey stations over 5 years, the effects of foundress group size (FGS) on colony survival rate and production of progeny were examined. The distribution pattern for the frequency of nests established by different numbers of foundresses fit a 0-truncated negative binomial distribution. The rate of nest failure up to the beginning of June decreased with FGS, and colony survival rate up to June and September increased with FGS. Although there were large variations among stations and years, the survival rate of colonies established by a single foundress (haplometrotic colonies) was significantly lower than that of colonies established by two or more foundresses (pleometrotic colonies). The number of new adults that emerged per colony up to the end of July increased with FGS, but there was no significant correlation between number of new adults per foundress and FGS. The number of potential foundresses produced per colony tended to increase with FGS, but there was no significant difference among the values produced per foundress for the three FGS categories. The percentage parasitism by an ichneumon parasitoid, Arthula formosana, tended to be higher in colonies established by a small number of foundresses. The relation between FGS and the productivity of the new foundresses was not statistically significant, suggesting that independent founding may be a better strategy for future subordinate foundresses. However, the long colony life span (mean 100 days, maximum 240 days) as compared with the shorter life span of foundresses (40 or 50 days) may be a good condition for the coexistence of many egg-layers in a colony.
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