Biomechanics of nectar foraging in orchid bees (Apidae: Euglossini)

In nectar feeding insects, biomechanical constraints related to proboscis extension, floral handling, and fluid ingestion may shape ecological relationships in pollinator communities. In this study, I review these constraints in a range of insect nectarivores and investigate biomechanical aspects of nectar ingestion in Neotropical orchid bees (Apidae: Euglossini) to provide insight into the partitioning of nectar resources among species.; First, I demonstrate that the four major genera of orchid bees (Apidae: Euglossini) are suction feeders and provide experimental evidence that the optimal nectar sugar concentration for one species, Euglossa imperialis , falls below optima for bee taxa that lap.; Second, I measure nectar intake as a function of nectar presentation (volume and feeding time), sucrose concentration, nectar viscosity, and ambient pressure. These results are compared with predictions from a model of suction feeding. Although behavioral motivation has the potential to influence some biomechanical assessments, the nectar feeding system of orchid bees is well-described by the mathematical model. However, results from ambient pressure reduction experiments suggest that the orchid bee proboscis is not a rigid tube, but may expand during nectar feeding.; Third, I use phylogenetic comparative methods to relate morphological features of orchid bees, namely body mass and proboscis length, to the mechanics of nectar feeding. While suction feeding bees consume nectars five times more slowly than lapping bees, nectar intake increases as body mass raised to the 0.6 power for both feeding modalities. Optimal nectar sugar concentrations fall between 30 and 40% sucrose independent of body mass, and the nectars orchid bees collect in nature also fall within this range. This comparative study also confirms a hypothesized cost to a long proboscis: a decline in nectar intake rate.; Lastly, I use phylogenetic comparative methods to test whether proboscis length in orchid bees is positively correlated with corolla length in two important groups of euglossine flowers, Costus and close-flowered Calathea. A longer proboscis is associated with deeper flowers, but, more significantly, the range of floral depths visited by euglossine bees increases with proboscis length. Consequently, the evolution of a long proboscis provides bees with a wider diversity of nectar resources to counterbalance biomechanical costs.