Phylogenetic relationships and the evolution of host preferences in the largest clade of brood parasitic bees (Apidae: Nomadinae).

Brood parasites (also known as cleptoparasites) represent a substantial fraction of global bee diversity. Rather than constructing their own nests, these species instead invade those of host bees to lay their eggs. Larvae then hatch and consume the food provisions intended for the host's offspring. While this life history strategy has evolved numerous times across the phylogeny of bees, the oldest and most speciose parasitic clade is the subfamily Nomadinae (Apidae). However, the phylogenetic relationships among brood parasitic apids both within and outside the Nomadinae have not been fully resolved. Here, we present new findings on the phylogeny of this diverse group of brood parasites based on ultraconserved element (UCE) sequence data and extensive taxon sampling with 114 nomadine species representing all tribes. We suggest a broader definition of the subfamily Nomadinae to describe a clade that includes almost all parasitic members of the family Apidae. The tribe Melectini forms the sister group to all other Nomadinae, while the remainder of the subfamily is composed of two sister clades: a "nomadine line" representing the former Nomadinae sensu stricto, and an "ericrocidine line" that unites several mostly Neotropical lineages. We find the tribe Osirini Handlirsch to be polyphyletic, and divide it into three lineages, including the newly described Parepeolini trib. nov. In addition to our taxonomic findings, we use our phylogeny to explore the evolution of different modes of parasitism, detecting two independent transitions from closed-cell to open-cell parasitism. Finally, we examine how nomadine host-parasite associations have evolved over time. In support of Emery's rule, which suggests close relationships between hosts and parasites, we confirm that the earliest nomadines were parasites of their close free-living relatives within the family Apidae, but that over time their host range broadened to include more distantly related hosts spanning the diversity of bees. This expanded breadth of host taxa may also be associated with the transition to open-cell parasitism.

Polarization Microscopy and Infrared Microspectroscopy of Integument Coverings of Diapausing Larvae in Two Distantly Related Nonsocial Bees.

The larvae of the two distantly related nonsocial bees Ericrocis lata (Apidae) and Hesperapis (Carinapis) rhodocerata (Melittidae), which develop mostly under arid desert areas of North America, and that differ in that they either spin (E. lata) or do not spin (H. rhodocerata) protective cocoons before entering diapause, produce transparent films that cover the larval integument. To understand the nature of these films, their responses to topochemical tests and their characteristics when examined with fluorescence and high-performance polarization microscopy and microspectroscopy were studied. A positive staining by Sudan black B, birefringence of negative sign, and a Fourier transform-infrared (FT-IR) spectrum typical of lipids were detected for the integument covering of both species. The FT-IR signature, particularly, suggests a wax chemical composition for these lipid coverings, resembling the waxes that are used as construction materials in the honey cells produced by social bees. Considering the arid environmental conditions under which these larvae develop, we hypothesize that their covering films may have evolved as protection against water depletion. This hypothesis seems especially appropriate for H. rhodocerata larvae, which are capable of undergoing a long diapause period in the absence of a protective cocoon.

Survey of Hatching Spines of Bee Larvae Including Those of Apis mellifera (Hymenoptera: Apoidea).

This article explores the occurrence of hatching spines among bee taxa and how these structures enable a larva on hatching to extricate itself from the egg chorion. These spines, arranged in a linear sequence along the sides of the first instar just dorsal to the spiracles, have been observed and recorded in certain groups of solitary and cleptoparasitic bee taxa. After eclosion, the first instar remains loosely covered by the egg chorion. The fact that this form of eclosion has been detected in five families (Table 1 identifies four of the families. The fifth family is the Andrenidae for which the presence of hatching spines in the Oxaeinae will soon be announced.) of bees invites speculation as to whether it is a fundamental characteristic of bees, or at least of solitary and some cleptoparasitic bees. The wide occurrence of these spines has prompted the authors to explore and discover their presence in the highly eusocial Apis mellifera L. Hatching spines were indeed discovered on first instar A. mellifera. The honey bee hatching process appears to differ in that the spines are displayed somewhat differently though still along the sides of the body, and the chorion, instead of splitting along the sides of the elongate egg, seems to quickly disintegrate from the emerging first instar in association with the nearly simultaneous removal of the serosa that covers and separates the first instar from the chorion. Unexpected observations of spherical bodies of various sizes perhaps containing dissolving enzymes being discharged from spiracular openings during hatching may shed future light on the process of how A. mellifera effects chorion removal during eclosion. Whereas hatching spines occur among many groups of bees, they appear to be entirely absent in the Nomadinae and parasitic Apinae, an indication of a different eclosion process.

Topochemistry, optical anisotropy and FT-IR microspectroscopy of the cocoon of Lithurgus chrysurus (Hymenoptera, Megachilidae).

A previous study has not revealed the participation of a mucous component in the cocoon wall of the solitary bee, Lithurgus chrysurus, differing from the cocoon structure reported for many other bee species. However, uncertainty remains, because only the median and rear zones of this cocoon type have thus far been analyzed. Here, we studied the front zone of this cocoon, searching its components and their organization, to fill this knowledge gap. Topochemical assays, polarization microscopy and Fourier transform-infrared (FT-IR) microspectroscopy were used to study cross sections from L. chrysurus cocoon. Three main layers differing in structural organization were found to compose the cocoon wall. Silk fibroins were assumed to constitute the filamentous threads of the inner and outer layers and the laminar structure of the intermediate layer. Deduced from its topochemical properties and FT-IR spectral signature, a foamy material containing mucin glycoproteins and carboxylated acid glycosaminoglycans was found in the intermediate layer. FT-IR analysis using a Savitzky-Golay 2nd-derivative and absence of linear dichroism and birefringence phenomena suggest that a random-coil secondary structure predominates in the foam component. Co-existence of α-helical and ß-sheet conformations is also hypothesized for the fibroin component of this cocoon. It is thus concluded that in addition to fibroin elements, a mucous component, likely contributed by a Malpighian tubule secretion, integrates the composition of the front zone of the cocoon wall of L. chrysurus. In addition, the FT-IR analysis of the inner layer silk of this cocoon suggests significant differences in comparison to the silk fibroins of the silkworm, and some minor spectral differences in comparison to published data on the honeybee silk, with respect to protein secondary structure.

Descriptions of mature larvae of the bee tribe emphorini and its subtribes (hymenoptera, apidae, apinae).

A description of the mature larvae of the bee tribe Emphorini based on representatives of six genera is presented herein. The two included subtribes, Ancyloscelidina and Emphorina, are also characterized and distinguished from one another primarily by their mandibular anatomy. The anatomy of abdominal segments 9 and 10 is investigated and appears to have distinctive features that distinguish the larvae of the tribe from those of related apine tribes.