Melikertini Engel

Engel, Michael S. & Xie, Jiaying, 2024, The Bee Fauna Of Eocene Fushun Amber (Hymenoptera: Apoidea), Bulletin of the American Museum of Natural History 2024 (469), pp. 1-81 : 32-33

Tribe Melikertini Engel

Melikertines are the most commonly encountered bees in Eocene amber and have been recovered from the Baltic (inclusive of Bitterfeld), Cambay, and Fushun amber deposits, thus spanning a rather impressive paleogeographical distribution from at least the Ypresian through Bartonian ( Engel and Davis, 2021). A species of melikertine has been discovered recently in Eocene Lublin amber ( Celary et al., 2023; J. Szwedo, personal commun.). No melikertines are currently known from after the Eocene-Oligocene transition and none have been discovered in older amber deposits. Likewise, they have yet to be found as compressions or impressions in contemporaneous sedimentary settings, such as the maar lakes of Messel or Eckfeld in Germany where electrapine and ctenoplectrelline bees have been recovered in addition to their more widely known amber inclusions ( Wappler and Engel, 2003; Wedmann et al., 2009; Wappler et al., 2015), and alongside early-diverging genera/subgenera of surviving tribes, such as Xylocopini and Bombini (Geier et al., in press; M.S.E., unpubl. data). The restriction of melikertines to amber may be a bias driven by their resin-collecting habits ( Engel and Davis, 2021). The tribe currently comprises 15 species in nine genera, inclusive of the species described herein (table 3). Currently available phylogenetic evidence supports melikertines as related to Meliponini , the stingless bees, and that these together are sister to the honeybees, Apini , with the bumble bees more further removed ( Engel, 2001; Schultz et al., 2001). Unfortunately, the fossil record of bumble bees is scant and in need of further revision (Wappler et al., 2012; Prokop et al., 2017; Dehon et al., 2019; M.S.E., unpubl. data), while that of Apini is richer but in even greater need of reconsideration ( Engel, 1998a, 1999b; Kotthoff et al., 2013; M.S.E., unpubl. data).

Melikertines were eusocial, likely living in colonies similar to those of modern stingless bees ( Engel, 1998b; Barden and Engel, 2021; Engel and Davis, 2021). For all but one of the species we know only the worker caste and therefore lack data for variations between workers and the other castes. Accordingly, it remains unknown whether some of the exaggerated morphologies observed in workers may also be present in queens or males. One would initially hypothesize that the queens lack these structures (e.g., facial protuberances), since they would seem to be associated with resin collection ( Engel and Davis, 2021), although it cannot be ruled out that they may also be deployed in nest construction or less likely in defense (given the morphologies known, none seem suitable as a defensive weapon). An extensive account of the tribe and its diversity and putative paleobiology was recently provided by Engel and Davis (2021) and is therefore not repeated here except to update their key to genera.