Demonstrating the importance of haplodiploidy in the evolution of eusociality among the Hymenoptera (bees, wasps, and ants) requires estimation of four parameters: relatedness between cooperating individuals, effective mating frequency, sex ratio, and rates of worker reproduction. Multilocus DNA fingerprinting techniques permitted the precise determination of these parameters for the primitively eusocial bee Augochlorella striata (Halictidae). DNA fingerprints revealed an unprecedented resolution of genetic relationships within colonies, detecting factors such as intraspecific nest parasitism and diploid males that confounded estimates of relatedness and sex ratio, respectively. Parameter estimates (i) corroborate recent evidence for queen-worker conflict over the sex ratio and (ii) implicate the role of haplodiploidy in the evolution of worker behavior.