Electroantennogram and behavioral responses of workers of the stingless bee Oxytrigona mediorufa to mandibular gland volatiles

Gas chromatography-mass spectrometric analysis showed that the mandibular gland secretion of workers of the stingless bee Oxytrigona mediorufa (Cockerell) (Hymenoptera: Apidae) is composed of 3-hepten-2,5-dione, 3-nonene-2,5-dione, 2-heptanone, hydrocarbons, tetradecyl, and hexadecyl acetates and minor compounds related to these. Behavioral and electroantennographic tests were carried out on conspecific workers to observe the effect of worker mandibular gland secretion, individual compounds (2-heptanone, 2-nonanone, and tetradecyl acetate), and a blend of these three. Bioassays showed that biting responses of O. mediorufa to the odor of the mandibular gland secretion were similar to that of 2-heptanone and to the three-component blend. Oxytrigona mediorufa workers exhibited antennal olfactory responses to the gland extract, 2-heptanone, and the synthetic mixture. The function of the mandibular gland secretion and 2-heptanone is discussed in terms of an alarm pheromone and defensive substances.     

The apid cuckoo bees of the Cape Verde Islands (Hymenoptera, Apidae)

The apid cuckoo bees of the Cape Verde Islands (Republic of Cape Verde) are reviewed and five species recognized, representing two genera. The ammobatine genus Chiasmognathus Engel (Nomadinae: Ammobatini), a specialized lineage of cleptoparasites of nomioidine bees is recorded for the first time. Chiasmognathus batelkaisp. n. is distinguished from mainland African and Asian species. The genus Thyreus Panzer (Apinae: Melectini) is represented by four species - Thyreus denoliisp. n., Thyreus batelkaisp. n., Thyreus schwarzisp. n., and Thyreus aistleitnerisp. n. Previous records of Thyreus scutellaris (Fabricius) from the islands were based on misidentifications.     

Influence of urbanisation on the prevalence of protozoan parasites of bumblebees

1. Increasing urbanisation is often cited as a cause of declining biodiversity, but for bumblebees there is evidence that urban populations of some species such as Bombus terrestris L. may be more dense than those found in agricultural landscapes, perhaps because gardens provide plentiful floral resources and nesting opportunities. 2. Here we examine the influence of urbanisation on the prevalence of the main protozoan parasites of bumblebees in west central Scotland. We would expect transmission rates and prevalence of parasites to be higher in high density host populations, all else being equal. 3. Workers of two bee species, B. terrestris and B. pascuorum, were sampled over a 45‐day period in mid to late summer, and parasites were detected in faeces and via dissection. A comparison of the two methods suggests that faecal sampling is considerably less sensitive than dissection, failing to detect infection in 27.8%, 55.1%, and 80% of cases of infection with the parasites Crithidia bombi, Nosema bombi, and Apicystis bombi, respectively. 4. For all three parasites, broad patterns of prevalence were similar, with prevalence tending to increase with urbanisation in B. terrestris but not in B. pascuorum. The different patterns of seasonal prevalence in the two bee species suggest that intraspecific transmission is more important that interspecific transmission. 5. Our observation of greater parasite prevalence among B. terrestris in urban compared with rural areas suggests that urban habitats may present greater opportunities for parasite transmission. Greater bee densities in urban areas may be the driving factor; however, further study is still needed. For example, differences in disease prevalence between habitats could be driven by differences in the types and abundance of flowers that are available, or in exposure to environmental stressors.     

Evidence for hilltopping in bumblebees?

1. Male bumblebees are known to exhibit a range of mate‐location behaviours, including perching on prominent objects and darting at passing queens, patrolling of scent‐marked flight routes, and waiting outside nest entrances for virgin queens to emerge. Here we provide evidence for a fourth strategy, known as hilltopping. This behaviour is widely known from a range of invertebrates, but has not previously been described in bumblebees. 2. We studied the distribution of bumblebees along transects ascending four hills in Scotland and demonstrate that, relative to workers, males of four bumblebee species or species groups (Bombus lapidarius, B. monticola, B. pascuorum, and B. lucorum/magnus/cryptarum/terrestris) tend to congregate at or near the tops of hills. This is, to our knowledge, the first evidence for hilltopping in bumblebees and the first record of any putative mate‐locating behaviour for male B. pascuorum, a very common species in Europe. 3. We note that, in common with most previous studies of mate‐locating behaviour in bumblebees, attraction of virgin queens and mating were not observed.     

Sterols of phytophagous and omnivorous species of Hymenoptera

The sterols of six species of Hymenoptera including two phytophagous species (Apis mellifera and Megachile rotundata) and four omnivorous species (Dolichovespula maculata, Vespula maculifrons, Formica exsectoides, and Solenopsis invicta) were isolated and identified. The two phytophagous species of bees have in common relatively high levels of 24-methylenecholesterol and very low levels of cholesterol (<1% of total sterols). The isofucosterol content (40.7%) of M. rotundata was nearly three times that of A. mellifera, but overall utilization of dietary sterols in the two species is similar in that neither is able to convert C₂₈ and C₂₉ phytosterols to cholesterol. All four omnivorous species are predatory to some extent, and the fact that their usual dietary sterols include high levels of chlosterol is reflected in the sterols isolated from these species, which contain 45–81% cholesterol. All six hymenopteran species appear to utilize dietary sterols for structural needs with little or no metabolic modification of the steroid structure.     

Exploring gene tree incongruence at the origin of ants and bees (Hymenoptera)

The fact that different phylogenomic data sets can lead to highly supported but inconsistent results suggest that conflict among gene trees in real data sets could be severe. We provide here a detailed exploration of gene tree space to investigate the relationships in Hymenoptera based on data obtained by Johnson et al. (Current Biology, 2013, 23, 2058), in which ants and Apoidea (bees and spheciform wasps) were recovered as sister groups, contradicting previous studies. We found high levels of topological variation among gene trees, several of them disagreeing with previously published hypotheses. To profile the dynamics of emerging support versus conflicting signal in combined analysis of data, we employed a novel method based on the incremental addition of randomized data to coalescence‐based phylogenetic inference. Although the monophyly of Aculeata and of Formicidae were consistently recovered using as little as 6.5% of the 308 available markers, signal for the Formicidae + Apoidea clade prevailed only after more than 50% of the loci were sampled. Still, non‐negligible support for alternative hypotheses remained until all genes were added to the analysis. Our results suggest that phylogenetic conflict is rather pervasive and not scattered as noise across individual gene trees because alternative topologies were recovered not from a specific subset, but from several random combinations of loci. Thus, even though phylogenetic signal recovered from full gene data sets was already dominant in much smaller ensembles, large amounts of data may be indeed necessary to overcome phylogenetic conflict.     

Impact of insecticidal proteins expressed in transgenic plants on bumblebee microcolonies

In order to assess the risk that insecticidal transgenic plants may pose for bumblebees, we tested whether Bombus terrestris (L.) (Hymenoptera: Apidae) workers are able to detect insecticidal proteins dissolved in sucrose solution and whether consumption of these proteins will affect survival and offspring production. Feeders containing either Bacillus thuringiensis toxin (Cry1Ab), Kunitz soybean trypsin inhibitor (SBTI), or Galanthus nivalis agglutinin (GNA) were offered to bumblebee colonies at low (0.01% wt/vol for SBTI and GNA, 0.001% for Cry1Ab) and high concentrations (0.1% for SBTI and GNA, 0.01% for Cry1Ab) together with a control (pure sucrose solution) in a glasshouse chamber. No difference was found in the number of visits and the duration of visits among the different concentrations for each of the insecticidal proteins, indicating that bumblebees do not discriminate the compounds. To investigate the impact of the different insecticidal proteins on B. terrestris, microcolonies were established by placing three newly emerged bumblebee workers in wooden boxes. Within a few days, a hierarchy in each microcolony was established and the dominant worker developed its ovaries and laid haploid eggs. Bumblebees were fed with Cry1Ab (0.01%), SBTI, or GNA (both at 0.01 and 0.1%) dissolved in sucrose solution and also fed mixed floral pollen for a maximum period of 80 days. Additionally, microcolonies with three drones each were established to measure individual bee longevity. While the Cry1Ab did not affect microcolony performance, the consumption of SBTI and especially GNA affected survival of B. terrestris workers and drones and caused a significant reduction in the number of offspring. The use of microcolonies appears to be well‐suited to measure lethal and sublethal effects of insecticidal proteins expressed in transgenic plants on bumblebees.     

Occurrence and morphometry of the hypopharyngeal glands inScaptotrigona postica Lat. (Hymenoptera, Apidae, Meliponinae)

As compared toApis mellifera where only workers have hypopharyngeal glands, inScaptotrigona postica, these glands occur in workers, queens and males. They are composed of two long axial ducts with many unicellular secretory alveoli interconnected by secretory canaliculi. The axial ducts are longer in males than in workers, but the alveolar areas of queens and males are generally smaller. In workers the alveoli have their greatest size in the nurses or middle-aged individuals while in queens and males they are larger in newly emerged individuals. The results indicate that the glands in workers may produce food for the brood as inA. mellifera, since they are well developed in the nurse workers. However, the function of the glands in queens and males remains to be clarified since these individuals have no part in brood care.