Chemoreceptor Diversity in Apoid Wasps and Its Reduction during the Evolution of the Pollen-Collecting Lifestyle of Bees (Hymenoptera: Apoidea).

Chemoreceptors help insects to interact with their environment, to detect and assess food sources and oviposition sites, and to aid in intra- and interspecific communication. In Hymenoptera, species of eusocial lineages possess large chemoreceptor gene repertoires compared with solitary species, possibly because of their additional need to recognize nest-mates and caste. However, a critical piece of information missing so far has been the size of chemoreceptor gene repertoires of solitary apoid wasps. Apoid wasps are a paraphyletic group of almost exclusively solitary Hymenoptera phylogenetically positioned between ant and bee, both of which include eusocial species. We report the chemosensory-related gene repertoire sizes of three apoid wasps: Ampulex compressa, Cerceris arenaria, and Psenulus fuscipennis. We annotated genes encoding odorant (ORs), gustatory, and ionotropic receptors and chemosensory soluble proteins and odorant-binding proteins in transcriptomes of chemosensory tissues of the above three species and in early draft genomes of two species, A. compressa and C. arenaria. Our analyses revealed that apoid wasps possess larger OR repertoires than any bee lineage, that the last common ancestor of Apoidea possessed a considerably larger OR repertoire (∼160) than previously estimated (73), and that the expansion of OR genes in eusocial bees was less extensive than previously assumed. Intriguingly, the evolution of pollen-collecting behavior in the stem lineage of bees was associated with a notable loss of OR gene diversity. Thus, our results support the view that herbivorous Hymenoptera tend to possess smaller OR repertoires than carnivorous, parasitoid, or kleptoparasitic species.

A study on taxonomy and phylogeny of immature stages of Sphecidae (Hymenoptera: Apoidea).

A taxonomic and phylogenetic study of Sphecidae based on morphology of last instar larvae and eggs is presented, including description of the family and a key to identify genera, tribes and subfamilies. Larval morphology of 12 species of Sphecidae was studied, along with four others used as outgroups (belonging to Ampulicidae, Crabronidae and Apidae). Thirty characters were listed from the morphological studies. Four genera were included in the analysis based only on literature. Thus, representatives of all the subfamilies and tribes of the Sphecidae were included in the analysis, except those of Stangeellini. The characters matrix was submitted to a parsimonious analysis using TNT version 1.5 and generated four equally parsimonious trees, with Length = 46, Consistence Index = 0.739, Retention Index = 0.878. The hypothesis of relationship suggested by the larvae and eggs is congruent with those suggested by the adult morphology in previous studies. The taxa Sphecidae, Sceliphrinae, Podiini, Sceliphrini, Prionychini and Ammophilinae, as well the assemblages Sceliphrinae + Chloriontinae and Sphecinae + Ammophilinae were supported by larval apomorphies. No apomorphy supporting the monophyly of Sphecinae and Sphecini was found.