Changes in the morphology and ultrastructure of the Dufour's gland during the life cycle of the bumble bee queen, Bombus terrestris L-(Hymenoptera : Bombini)

The Dufour's gland is found closely associated with the sting apparatus of all female hymenopterans, playing multiple roles among bees. In some specie s of Bombus the gland may be involved in production of nestmate recognition pheromones, but in B. terrestris its function is not certain yet. The morp hology of the :Dufour's gland of B. terrestris queens and the ultrastructur al features of its cells were studied in different ages and behavioural sta ges using routine transmission electron microscopy. Measurements of the len gth and the diameter of the gland in the same conditions were also made. Th e Dufour's gland of the queen increases significantly in size (both in leng th and in diameter) with age and reproductive activity The ultrastructural features of the gland show electrondense material that comes from the haemo lymph. This material is also present in the intercellular spaces, and is co nducted to the subcuticular space, to be released directly into the glandul ar lumen. Hence at least part of the secretion is probably taken up directl y from the haemolymph. The ultrastructural features indicate a more active phase of the gland corresponding to the period of egg-laying of the queen, and a decrease in activity when the queen is in hibernation as well as afte r the competition point. In conclusion, the gland is probably involved in r eproduction, more specifically, in the marking off eggs.