Out of curiosity, I consulted the book by Michener, 2007, The Bees of the World, Second edition. As regards Meliponini, the Author writes that they " have morphologically as well as behaviorally very different female castes, queen and worker" (p. 803), but he doesn't indicate - if I'm not mistaken -  the morphological differences. A few pages later (p. 813), before the keys to the genera of Meliponini, he writes that "the keys below are based primarily on workers. [...] Queens have been available for only a few taxa". Furthermore, under the genus Scaptotrigona, no indication is provided as regards morphological differences between queens and workers. It seems to be clear that queens of various genera of Meliponini are unknown to the Author... I am surprised also by the difficulty in finding useful pictures in internet for the castes of genera belonging to the tribus. I haven't further comments to add, and I suggest to try to find something in more recent literature.

Best regards,

Rinaldo Nicoli

 Dear Rinaldo

Thanks your coments, as a matter of fact there is a gap in these informations... Kindly, Geraldo