BORRELL, Brendan J.; Univ. of California, Berkeley: Suction Feeding in the Orchid Bees

Energy flux during nectar feeding is optimal at an intermediate nectar sugar concentration, which depends on the morphology of the feeding apparatus and the modality of fluid feeding. Biophysical models predict that a shift from capillary-based lapping to suction feeding will lead to a downward shift in this optimal sugar concentration. Here, I demonstrate that this type of shift has occurred in the orchid bees (Apidae: Euglossini), providing a test of these theoretical predictions. Whereas most bees use a relatively generalized and short proboscis to consume nectar via lapping motions of their hairy ‘tongue’, in all four genera of orchid bees, the glossa is completely extended and static during feeding. Surgical removal of the glossa has no effect on nectar intake rate, indicating that the glossa is not an essential component of nectar transport in these bees. In concurrence with biophysical predictions, energy intake optima for orchid bees are similar to those of other suction-feeding insects (30-40% sucrose), whereas optima for bumblebees, honeybees, and stingless bees lie between 50-60% sucrose. In the wild, orchid bees also collect more dilute nectars than sympatric bees, which are known to lap nectar.