TROPHIC ASPECTS OF CASTE DETERMINATION IN HALICTUS-LIGATUS, A PRIMITIVELY EUSOCIAL SWEAT BEE

Caste determination in primitively eusocial sweat bees is thought to b e due to an interacting suite of factors, including size of the larval provision mass, time of year, and social context of the nest into whi ch a young female emerges. Newly emerged gynes are significantly fatte r than newly emerged workers, suggesting the existence of larval caste determination cues. Since photoperiod, temperature, and interactions with nestmates were unlikely to affect larval caste determination, we compared the sizes and contents of larval provision masses destined to produce either workers or gynes. Gyne-destined larvae consumed pollen masses that were larger and contained slightly more sugar than those of worker-destined larvae. We suggest that sugar content is one cue wh ich prompts the development of fat reserves in gyne-destined females b ut not in worker-destined females. The amount of fat possessed by a ne wly emerged female influences her chances of successfully entering dia pause shortly after emergence. Therefore, small, lean females may be m ore susceptible to behavioural control by queens and more likely to be come workers, while large, fat females would be more likely to become gynes.