Research into the driving forces behind spatial arrangement of wasp nests has considered abiotic environmental factors, but seldom investigated attraction or repulsion towards conspecifics or heterospecifics. Solitary female digger wasps (Hymenoptera) often nest in dense aggregations, making these insects good models to study this topic. Here, we analysed the nesting patterns in an area shared by three species of the genus Bembix, in a novel study to discover whether female wasps are attracted to or repulsed by conspecific nests, heterospecific nests or their own previously established nests when choosing nest‐digging locations. Early in the season, each species showed a clumping pattern of nests, but later in the season, a random distribution of nests was more common, suggesting an early conspecific attraction. Such behaviour was confirmed by the fact that females started building their nests more frequently where other females of their species were simultaneously digging. The distances between subsequent nests dug by individual females were shorter than those obtained by random simulations. However, this pattern seemed to depend on the tendency to dig close to conspecifics rather than remain in the vicinity of previous nests, suggesting that females' experience matters to future decisions only on a large scale. Nesting patches within nest aggregations largely overlapped between species, but the nests of each species were generally not closer to heterospecific nests than expected by chance, suggesting that females are neither repulsed by, nor attracted to, congenerics within nest aggregations. A role of the spatial distribution of natural enemies on the observed nesting patterns seemed unlikely. Bembix digger wasp nest aggregations seem thus to be primarily the result of female–female attraction during nest‐settlement decisions, in accordance with the ‘copying’ mechanisms suggested for nesting vertebrates.

Although inter-individual diet variation is common in predatory wasp populations, the factors accounting for such variation are still largely unknown. Here, we asked if paired diet dissimilarity in three species of digger wasps correlates with morphological distance and inter-nest distance, two factors previously linked to diet partitioning in vertebrates. Results sharply differed among species and generations. All sampled populations showed significant inter-individual diet variation for prey taxa, but only in half of the cases for prey size. In one generation of two species [Bembix zonata Klug and Stizus continuus (Klug)], similar-sized wasps had similar prey taxonomic spectra (and for S. continuus also similar prey size spectra), a phenomenon which probably reduces intra-specific competition. In addition, B. zonata females nesting closer to each other had more similar prey taxonomic spectra, suggesting that distant females probably hunt on different patches that harbour different prey species. For the females of a further species (Bembix merceti Parker), pairwise size difference and inter-nest distance did not affect prey dissimilarity. Both morphological distance and inter-nest distance are potentially important in shaping the overlap of individual resource use in wasps, though probably only in certain conditions such as a highly clumped distribution of nests and size-related constraints on prey selection.

Abstract. Bembix is a cosmopolitan genus with more than 300 species distributed all over the world. The females of these wasps dig burrows in the ground and hunt for fl ies to feed their larvae. Current knowledge of the nesting behaviour of most Palaearctic species (around 50) is limited. In this study, we provide data on the nest structure, nesting activity, natural enemies and prey captured by three Bembix sand wasps present on the Iberian Peninsula: B. zonata, B. fl avescens bolivari and B. merceti. We also analyze the prey spectrum of the three species, comparing our data with those available from previous studies. B. zonata exhibits the greatest selectivity index (and the narrowest niche width), capturing mainly Syrphidae to provision its nests. B. merceti shows the greatest niche width in comparison with the other two species. The inter-annual differences in the diet of B. merceti are important and are probably due to the ability of this wasp to change from one prey resource to another, depending on its availability.Résumé. Notes sur les proies, la nidifi cation et les ennemis naturels de trois espèces de Bembix (Hymenoptera : Crabronidae) de la péninsule Ibérique. Le genre Bembix est cosmopolite avec plus de 300 espèces à travers le monde. Les femelles creusent des terriers dans le sol et capturent des diptères qui servent de provision à leurs larves. Les connaissance actuelles sur le comportement de nidifi cation de la plupart des espèces européennes (ca 50) sont assez limitées. Dans le présent travail, les auteurs abordent la structure du nid, l'activité de nidifi cation, les ennemis naturels et les proies capturées par 3 espèces de Bembix présentes dans la péninsule ibérique: B. zonata, B. fl avescens bolivari et B. merceti. Ils analysent également le spectre des proies des trois espèces et le comparent aux études antérieures. B. zonata, qui présente le plus grand indice de sélectivité et la niche la plus étroite, utilise surtout des Syrphidae comme proies. B. merceti présente la niche la plus large par rapport aux deux autres espèces. Les différences inter-annuelles dans le régime alimentaire de B. merceti sont importantes et sont probablement dues à la faculté qu'a l'espèce de passer d'un type de proie à l'autre selon les ressources disponibles.

The wasp family Chrysididae (cuckoo wasps, gold wasps) comprises exclusively parasitoid and kleptoparasitic species, many of which feature a stunning iridescent coloration and phenotypic adaptations to their parasitic life style. Previous attempts to infer phylogenetic relationships among the family’s major lineages (subfamilies, tribes, genera) based on Sanger sequence data were insufficient to statistically resolve the monophyly and the phylogenetic position of the subfamily Amiseginae and the phylogenetic relationships among the tribes Allocoeliini, Chrysidini, Elampini, and Parnopini (Chrysidinae). Here, we present a phylogeny inferred from nucleotide sequence data of 492 nuclear single-copy genes (230,915 aligned amino acid sites) from 94 species of Chrysidoidea (representing Bethylidae, Chrysididae, Dryinidae, Plumariidae) and 45 outgroup species by combining RNA-seq and DNA target enrichment data. We find support for Amiseginae being more closely related to Cleptinae than to Chrysidinae. Furthermore, we find strong support for Allocoeliini being the sister lineage of all remaining Chrysidinae, whereas Elampini represent the sister lineage of Chrysidini and Parnopini. Our study corroborates results from a recent phylogenomic investigation, which revealed Chrysidoidea as likely paraphyletic.

Insect brood parasites have evolved a variety of strategies to avoid being detected by their hosts. Few previous studies on cuckoo wasps (Hymenoptera: Chrysididae), which are natural enemies of solitary wasps and bees, have shown that chemical mimicry, i.e., the biosynthesis of cuticular hydrocarbons (CHC) that match the host profile, evolved in several species. However, mimicry was not detected in all investigated host-parasite pairs. The effect of host range as a second factor that may play a role in evolution of mimicry has been neglected, since all previous studies were carried out on host specialists and at nesting sites where only one host species occurred. Here we studied the cuckoo wasp Parnopes grandior, which attacks many digger wasp species of the genus Bembix (Hymenoptera: Crabronidae). Given its weak host specialization, P. grandior may either locally adapt by increasing mimicry precision to only one of the sympatric hosts or it may evolve chemical insignificance by reducing the CHC profile complexity and/or CHCs amounts. At a study site harbouring three host species, we found evidence for a weak but appreciable chemical deception strategy in P. grandior. Indeed, the CHC profile of P. grandior was more similar to all sympatric Bembix species than to a non-host wasp species belonging to the same tribe as Bembix. Furthermore, P. grandior CHC profile was equally distant to all the hosts’ CHC profiles, thus not pointing towards local adaptation of the CHC profile to one of the hosts’ profile. We conducted behavioural assays suggesting that such weak mimicry is sufficient to reduce host aggression, even in absence of an insignificance strategy, which was not detected. Hence, we finally concluded that host range may indeed play a role in shaping the level of chemical mimicry in cuckoo wasps.