A Monograph of the Baltic Amber Bees and Evolution of the Apoidea (Hymenoptera)

Abstract The bees found as Baltic amber inclusions are revised and the history of studies on these fossils is briefly reviewed. In total this subtropical Eocene fauna contains 36 species and 18 genera, all extinct. These are classified here into nine tribes, six subfamilies, and five families of which six tribes and one family are unknown in the modern fauna. The following taxa are described as new to science: PALEOMELITTIDAE, new family; Boreallodapini, Electrobombini, Eomacropidini, Melikertini, Protolithurgini, new tribes; Ctenoplectrellina, new subtribe; Boreallodape, Electrobombus, Electrolictus, Eomacropis, Glaesosmia, Liotrigonopsis, Melissites, Paleomelitta, Protolithurgus, Succinapis, Thaumastobombus, new genera; Boreallodape baltica, B. mollyae, B. striebichi, Ctenoplectrella cockerelli, C. grimaldii, Electrapis krishnorum, Electrobombus samlandensis, Electrolictus antiquus, Eomacropis glaesaria, Glaesosmia genalis, Glyptapis densopunctata, G. disareolata, Liotrigonopsis rozeni, Melikertes clypeatus, Melissites trigona, Paleomelitta nigripennis, Protobombus basilaris, Protolithurgus ditomeus, Succinapis goeleti, S. micheneri, S. proboscidea, Thaumastobombus andreniformis, new species (seven new family-, 11 new genus-, and 22 new species-group taxa). The genus Electrapis is found to be paraphyletic and the subgenera Melikertes, Roussyana, and Protobombus are given generic status outside of Electrapis. The subtribe Electrapina is elevated to tribal rank among the corbiculate Apinae and the subfamily Glyptapinae of Cockerell is reduced to subtribal rank within Osmiini. The genera Chalcobombus and Sophrobombus are newly synonymized with Protobombus. Glyptapis reducta Cockerell is synonymized with G. fuscula Cockerell, Electrapis minuta Kelner-Pillault with Apis palmnickenensis Roussy, Ctenoplectrella splendens Kelner-Pillault and C. dentata Salt both with C. viridiceps Cockerell, Electrapis apoides Manning and Chalcobombus humilis Cockerell both with Protobombus indecisus Cockerell, and Electrapis bombusoides Kelner-Pillault with E. tornquisti Cockerell (new synonymies). The following new combinations are proposed: Electrapis martialis (Cockerell), Melikertes proavus (Menge), M. stilbonotus (Engel), Kelneriapis eocenica (Kelner-Pillault), Protobombus fatalis (Cockerell), P. hirsutus (Cockerell), and Electrapis martialis (Cockerell) (new combinations). A lectotype is designated for Electrapis minuta Kelner-Pillault and neotypes designated for Apis meliponoides Buttel-Reepen, A. palmnickenensis Roussy, Chalcobombus humilis Cockerell, C. hirsutus Cockerell, C. martialis Cockerell, Ctenoplectrella dentata Salt, C. viridiceps Cockerell, Electrapis tornquisti Cockerell, Glyptapis reticulata Cockerell, G. neglecta Salt, Protobombus indecisus Cockerell, P. tristellus Cockerell, and Sophrobombus fatalis Cockerell. The subfamily Xylocopinae is recorded for the first time from amber, and the families Halictidae and Melittidae are confirmed as occurring in Baltic amber. The oldest fossils of the Halictidae, Megachilidae (Lithurginae and Megachilinae), Melittidae, and Xylocopinae are reported and described herein. Keys are presented for the identification of the Baltic amber bees. Three new recent taxa are also proposed: Penapini, Redivivini, and Meliturgulini (new tribes). Cladistic analyses of the Lithurginae, Xylocopinae, and corbiculate Apinae are presented. Preliminary investigation of lithurgine relationships demonstrates that the fossil, Protolithurgus, is sister to extant genera of the subfamily and that Lithurgus s.s. is likely paraphyletic with respect to Lithurgopsis and Microthurge. Xylocopine relationships are generally in accord with those previously proposed: Xylocopini sister to all other tribes and Manueliini sister to the abruptly narrowed mandible tribes (i.e., Ceratinini, Allodapini, and Boreallodapini). Boreallodapini, despite some apparently apomorphic similarities with Ceratinini, is supported as sister to Allodapini. The paleontological evidence for corbiculate bee phylogeny reinforces traditional concepts over relationships of these tribes and contradicts recent molecular studies. Two extinct corbiculate tribes are based on specimens that exhibit worker morphologies indicative of advanced eusocial behavior and are related to the living, advanced eusocial tribes Apini and Meliponini, supporting a hypothesis of a single origin for this behavioral characteristic. The composition of the Eocene bee fauna of Europe is discussed. The fauna is predominantly composed of long-tongued bees, but some short-tongued bees are represented in the families Halictidae, Paleomelittidae, and Melittidae. Bees in Baltic amber are generally allied with groups currently inhabiting sub-Saharan Africa and southeast Asia, a biogeographic pattern common to many Baltic amber groups. The phylogeny and origin of bees are discussed. The bees are a derived, monophyletic group of the spheciform wasps and presumably arose sometime in the earliest mid-Cretaceous after the origin of angiosperms. Reports of bees from Jurassic strata or earlier are all refuted. All available evidence supports the idea that bees originated shortly after flowering plants and diversified into higher lineages contemporaneously with the radiations of angiosperms. Major bee lineages (i.e., families) were thus presumably established by the Late Cretaceous. A catalog of bees presently known in amber and copal is appended as is a catalog of family- and genus-group names for fossil bees (both amber inclusions and compression fossils). A preliminary outline of the tribal classification of Recent and fossil bees with their geological distribution is presented (with three new family-group taxa for living bees). ZUSAMMENFASSUNG Die als Inklusen des Baltischen Bernsteins nachgewiesenen Bienen werden revidiert und ihre Erforschungsgeschichte kurz dargestellt. Insgesamt umfasst diese subtropische Fauna des Eozäns 36 Arten und 18 Gattungen, die alle ausgestorben sind. Diese werden in neun Tribus, sechs Unterfamilien, und fünf Familien klassifiziert, von denen sechs Tribus und eine Familie in der heutigen Fauna unbekannt sind. Die folgenden Taxa sind neu für die Wissenschaft: PALEOMELITTIDAE, fam. nov.; Boreallodapini, Electrobombini, Eomacropidini, Melikertini, Protolithurgini, tribus nov.; Ctenoplectrellina, subtribus nov.; Boreallodape, Electrobombus, Electrolictus, Eomacropis, Glaesosmia, Liotrigonopsis, Melissites, Paleomelitta, Protolithurgus, Succinapis, Thaumastobombus, gen. nov.; Boreallodape baltica, B. mollyae, B. striebichi, Ctenoplectrella cockerelli, C. grimaldii, Electrapis krishnorum, Electrobombus samlandensis, Electrolictus antiquus, Eomacropis glaesaria, Glaesosmia genalis, Glyptapis densopunctata, G. disareolata, Liotrigonopsis rozeni, Melikertes clypeatus, Melissites trigona, Paleomelitta nigripennis, Protobombus basilaris, Protolithurgus ditomeus, Succinapis goeleti, S. micheneri, S. proboscidea, Thaumastobombus andreniformis, spec. nov. (sieben neue Familien-, 11 neue Gattungs-, und 22 neue Artengruppentaxa). Die Gattung Electrapis ist paraphyletisch, und die Untergattungen Melikertes, Roussyana, und Protobombus werden unabhängig von Electrapis als Gattungen akzeptiert. Die Untertribus Electrapina erhält den Rang einer Tribus innerhalb der corbiculaten Apinae, und die Unterfamilie Glyptapinae von Cockerell wird als Untertribus innerhalb der Osmiini interpretiert. Die Gattungen Chalcobombus und Sophrobombus werden neu mit Protobombus synonymisiert. Folgende Arten werden miteinander synonymisiert: Glyptapis reducta Cockerell mit G. fuscula Cockerell, Electrapis minuta Kelner-Pillault mit Apis palmnickenensis Roussy, Ctenoplectrella splendens Kelner-Pillault und C. dentata Salt beide mit C. viridiceps Cockerell, Electrapis apoides Manning und Chalcobombus humilis Cockerell beide mit Protobombus indecisus Cockerell, Electrapis bombusoides Kelner-Pillault mit E. tornquisti Cockerell (neue Synonyme). Die folgenden Kombinationen werden neu eingeführt: Electrapis martialis (Cockerell), Melikertes proavus (Menge), M. stilbonotus (Engel), Kelneriapis eocenica (Kelner-Pillault), Protobombus fatalis (Cockerell), P. hirsutus (Cockerell), und Electrapis martialis (Cockerell) (neue Kombinationen). Ein Lectotypus wird für Electrapis minuta Kelner-Pillault festgelegt. Für folgende Arten werden Neotypen designiert: Apis meliponoides Buttel-Reepen, A. palmnickenensis Roussy, Chalcobombus humilis Cockerell, C. hirsutus Cockerell, C. martialis Cockerell, Ctenoplectrella dentata Salt, C. viridiceps Cockerell, Electrapis tornquisti Cockerell, Glyptapis reticulata Cockerell, G. neglecta Salt, Protobombus indecisus Cockerell, P. tristellus Cockerell, und Sophrobombus fatalis Cockerell. Die Unterfamilie Xylocopinae wird erstmals in Bernstein nachgewiesen, und das Vorkommen der Familien Halictidae und Melittidae in Baltischem Bernstein wird bestätigt. Die ältesten Fossilien der Halictidae, Megachilidae (Lithurginae und Megachilinae), Melittidae, und Xylocopinae werden nachgewiesen und beschrieben. Bestimmungsschlüssel für die Bienen des Baltischen Bernsteins werden erstellt. Drei rezenten Taxa sind neu: Penapini, Redivivini, und Meliturgulini (tribus nov.). Kladistische Analysen der Lithurginae, Xylocopinae, und der corbiculaten Apinae werden vorgestellt. Vorläufige Untersuchungen der verwandtschaftlichen Beziehungen der Lithurginae zeigen, dass die fossile Protolithurgus Schwestergruppe der rezenten Gattungen der Lithurginae ist. Außerdem ist Lithurgus s.s. wahrscheinlich paraphyletisch in Bezug auf Lithurgopsis und Microthurge. Die Verwandtschaftsbeziehungen der Xylocopinae stimmen grundsätzlich mit den bisher angenommenen überein: Die Xylocopini sind die Schwestergruppe aller übrigen Tribus, während die Manueliini die Schwestergruppe aller Tribus mit Arten mit abrupt verschmälerten Mandibeln ist (z.B. Ceratinini, Allodapini, und Boreallodapini). Boreallodapini wird a