Functional Morphology of the Honey Stomach Wall of the European Honey Bee (Hymenoptera: Apidae)

The crop, or honey stomach, of the honey bee, Apis mellifera L. (Hymenoptera: Apidae), is invested in cords of muscles that are numerous enough, in both latitudinal and longitudinal directions, to fully enclose and confine the underlying, cuticle-lined epithelium. Although appressed against the inner wall of this enclosure by the crop's contents, the epithelium is largely free of ligations that would immobilize it. It can therefore slide on the inner wall and undergo extensive pleating as needed to conform to the diameter of the enclosure, regardless of the extent of contraction or distention. The two primary components of the epithelial layer, epidermal cells and procuticle, can undergo extreme compression to maintain pleats while enduring the pressure exerted by the volume of crop contents. During engorgement with nectar, the muscular enclosure relaxes to larger and larger diameters. Correspondingly, pleats unfold as needed. During dispensation of nectar in the hive, the muscular enclosure contracts and forces the epithelium to pleat itself again. Pleats are present in even the most grossly distended crops, indicating that capacity is not a limiting factor in the volume of nectar a bee can accumulate during foraging. Individual pleats are appressed, too, indicating that a lubricating, cohering substance occurs between them.