SEASONAL VARIATION IN THE ONSET OF EGG LAYING IN A PRIMITIVELY EUSOCIAL WASP: IMPLICATIONS FOR THE EVOLUTION OF SOCIALITY

When freshly eclosed females of the primitively eusocial PSP. Ropa/idia marginata are isolated into individual cages, only about half of diem build nests and lay eggs and those that do so take a long and variable amount of ti8le (Mean:t S D =66:t 37 days) before they lay their first egg. Part of the reason for this delay is because, when kept In isolation, no wasp begins to lay eggs during a period of approximately 82 days from mid-October to early January. Was ~ maintained at a constant temperature of 26:tl°C however initiate egg laying throughout the year, suggesting that the low temperatures during mid-October to early January may be at least one factor that makes this period unfavourable for was ~ maintained at room temperature. Egg laying continues more or less normally throughout October-January however, In all natural and laboratory colonies 5t\MIied. Natural colonies of R. marginata are initiated throughout the year and often by grou ~ of females. Huddling together is a striking feature of the wasps especially on cold mornings. We therefore suggest that the isolated animals in our experiment are unable to lay eggs during the coldest part of the year because of their inability to huddle together, share metabolic heat and perform "co-operative thenooreguiation". Such "co-operative thermoregulation " may thus be another factor that facilitates the evolution of socialitY