Born to be bee, fed to be worker? The caste system of a primitively eusocial insect

The patterns of variation in adult body size, weight, fat content and food provisioned to the first and second brood indicate that H. scabiosae has dimorphic females. The first-brood females were significantly smaller, lighter and had lower fat reserves than the second-brood females and foundresses. The first-brood females were also less variable in size and fat content, and developed on homogeneously smaller pollen provisions. Foundresses were larger than gynes of the previous year, suggesting that small females were less likely to survive the winter.The marked size dimorphism between females produced in the first and second brood and the consistently smaller pollen provisions provided to the first brood suggest that the first brood females are channelled into a helper role during their pre-imaginal development. As a large body size is needed for successful hibernation, the mother may promote helping in her first brood offspring by restricting their food provisions. This pattern supports the hypothesis that parental manipulation may contribute to promote worker behaviour in primitively eusocial halictids.The hallmark of eusociality is reproductive division of labour between generations, a surprising social organization by which some individuals become functionally sterile helpers [1]. Primitively eusocial species are excellent systems to study the proximate mechanisms and ultimate causes leading to eusociality, because helpers have retained the ancestral ability to breed independently and may thus obtain both direct fitness benefits through reproduction and indirect fitness benefits by helping relatives [2-4].Primitively eusocial halictids have a low degree of morphological differentiation between queens and helpers and a high degree of behavioural flexibility in both types of individuals [2]. As a result, females have multiple reproductive options that result in diverse types of social organisation. Many primitively eusocial species live in temperate zones, where