A comparative study of the cardia and cardiac valves in corbiculate bees (Hymenoptera, Apinae)

The present study compares the structure of the cardiac valve and the cardi a among tribes of corbiculate bees. Seventeen species of stingless bees (Me liponini), one species of honeybee (Apini), one species of bumblebee (Bombi ni) and five species of orchid bees (Euglossini) were analyzed as an in-gro up, while fifteen species distributed among Centridini, Eucerini, Exomalops ini, Emphorini, Xylocopinae, Megachilidae and Halictidae as out-groups. The results showed that the cardiac valve is long and tubular in Apini, Bombin i and Meliponini and frequently has glycogen storage, while it is short and foliaceous in the Euglossini and out-groups. The anteriormost epithelium o f the midgut is differentiated in a long region named cardia in Meliponini, it is absent in Apini and Bombini, while being very short in Euglossini an d outgroups. Anatomically this anteriormost midgut portion in Meliponini is smooth, that is, without external circumvolutions of the midgut wall, whic h is present in the rest of the midgut and in the entire length of this dig estive organ in the other bees. These results were analyzed using cladistic methods. The results suggest that the presence of a long cardia and the an teriormost midgut portion without circumvolutions are autapomorphies for Me liponini, while the absence of cardia is a synapomorphy that justify ApiniBombini as a monophyletic group. Euglossini is the most similar to the ance stor and can be considered as a sister-group of other corbiculate Apinae.