Diet quantity influences caste determination in honey bees (Apis mellifera)

In species that care for their young, provisioning has profound effects on
offspring fitness. Provisioning is important in honey bees because
nutritional cues determine whether a female becomes a reproductive queen
or sterile worker. A qualitative difference between the larval diets of
queens and workers is thought to drive this divergence; however, no single
compound seems to be responsible. Diet quantity may have a role during
honey bee caste determination yet has never been formally studied. Our
goal was to determine the relative contributions of diet quantity and
quality to queen development. Larvae were reared in vitro on nine diets
varying in amount of royal jelly and sugars, which were fed to larvae in
eight different quantities. Once adults eclosed, the queenliness was
determined using Principal Component Analysis (PCA) on seven morphological
measurements. We found that larvae fed the largest quantities of diet were
indistinguishable from hive reared queens, independent of the proportion
of protein and carbohydrate in the diet. Neither protein nor carbohydrate
content had a significant influence on the first principle component
(PC1), which explained 64.4% of the difference between queens and workers.
Instead, the total quantity of diet explained a significant amount of the
variation in PC1. Large amounts of diet in the final instar were capable
of inducing queen traits, contrary to received wisdom that caste
determination can only occur in the third instar. These results indicate
that total diet quantity fed to larvae may regulate the difference between
queen and worker castes in honey bees.