consequences in that during seasons where males are more abundant, a smaller proportion of nests contain eusocial colonies, and the average number of workers per nest is lower. Mating behavior Like most bee species, mating in H. rubicundus occurs on the ground or vegetation in and around the nest aggregation. Males may hover around their natal nest and wait to encounter females that are entering or leaving a surrounding nest. Gynes are those females that leave the nest site after mating and enter a dormant state (diapause), and restart the cycle the following spring, while worker females, if they mate, remain in the natal nest. In this species, there are foundress gynes and non-gynes (who can be replacement queens or workers). The gynes and non-gynes are distinct groups, as gynes mate, do not work, and enter diapause (to become foundresses), while non-gynes work and do not diapause. There is evidence that male abundance may be the factor triggering this distinction early in life; if there is an abundance of males, a virgin female is more likely to encounter males and mate early shortly after emergence, and make a caste switch into being a gyne. If she is left unmated for two or three days, however, she will likely stay a non-gyne, even if she mates later on; no female who began acting as a worker (pollen-collecting behavior, typically starting within two or three days after emergence) was ever found to return the following season. Halictus rubicundus is the first bee species documented to have mixed broods containing both gynes and non-gynes, and it was previously thought that non-gynes and gynes were always produced in separate broods. Sex ratio effects on sociality Male abundance appears to have a major effect on deciding the social behavior within a population; the best predictor for a female's fate (future foundress gyne versus worker non-gyne) is the relative male abundance in proportion to virgin females on the first day a given virgin female emerges as an adult (i.e., if there are 10 males and 10 virgin females on one day, each female has a 50% chance of becoming a gyne, but if the following day there are 15 males and only 5 virgin females, then 75% of those females will become gynes). Warmer temperatures during the first brood provisioning phase in the spring leads to a higher ratio of male to female offspring, and a