Antennal circulatory organ of Apis mellifera L. (Hymenoptera: Apidae) and other Hymenoptera: functional morphology and phylogenetic aspects

The antennal circulatory organs of 38 species of Hymenoptera were investigated by means of serial semithin sections, SEM and TEM. In Apis, this organ consists of an unpaired ampulla from which blood vessels that extend into the antennae originate. The ampulla is a very delicate structure of elastic connective tissue. Its lumen communicates with the head hemocoel via numerous perforations in its wall. No specific ampulla muscles exist; contraction of pharynx dilators causes compression of the ampulla, whereby hemolymph is forced into the antennae.

An absence of directly-acting muscles is common to the functional morphologies of the antennal circulatory organ in all investigated Hymenoptera. Some anatomical characters of this organ, however, vary among taxa: (i) presence of one or two ampullae, (ii) optional dorsal hemolymph channel, which connects the ampulla with the dorsal vessel, (iii) optional ampulla pumping case formed by cuticular apophyses, and (iv) differences in shape and number of the ampulla openings. The distribution of these characters is discussed along the current views on the phylogeny of Hymenoptera. Comparison with other insect orders indicates an autapomorphic status for the basic functional morphology of the antennal circulatory organ in Hymenoptera.