honey bee crop

Crop of honey bee worker when empty (top) and filled with nectar (bottom). After Winston (1987, fig. 3.15) [1].

The crop (also called honey stomach or honey sack) is a specialized part of foregut. It is similar to distensible sack. The main function of the crop is transport and storage of liquid food (water, nectar and honeydew). Another function of crop is uptake of water from its lumen [2]. This is possible thanks to aquaporins - proteins which can transport water across membranes. The proteins are present in the crop epithelium [2]. The uptake of water from crop can be important for processing of nectar (or honeydew) and production of honey. This can explain why nectar in crop contains more sugar than nectar collected from flowers [3] but see [4]. In earlier studies it was suggested that inner crop walls are impermeable to water [5][6].
The crop wall consists of three layers: epithelium and two layers of muscles [7]. The innermost epithelium is covered with cuticle. It is extremely folded which allows increase of the crop volume.
The volume of the crop can increase about ten times during filling. When filled with food the crop is not distended uniformly but the dorsal side is stretching more than the ventral side [8].
Inside honey bee crop there are present lactic bacteria [9].