Floral Cues of Non-host Plants Attract Oligolectic Chelostoma rapunculi Bees

Oligolectic bees are highly dependent on the availability of the host plants to which they are specialized. Nevertheless, females of Chelostoma rapunculi have recently been monitored occasionally to visit Malva moschata and Geranium sanguineum flowers, in addition to their well-known Campanula spp. hosts. The questions therefore arise which floral cues promote visits to non-host plants. As host-specific floral cues are key attractants for oligolectic bees, we have studied the attractiveness of olfactory and visual cues of the established host Campanula trachelium in comparison to the non-host plants G. sanguineum and M. moschata in behavioral experiments. Chemical and electrophysiological analyses of the floral scent and spectral measurements of floral colors were used to compare and contrast host and non-host plants. The behavioral experiments showed that foraging-naïve bees, in particular, were attracted by olfactory cues of the non-host plants, and that they did not favor the Campanula host scent in choice experiments. Many electrophysiologically active floral volatiles were present in common in the studied plants, although each species produced an individual scent profile. Spiroacetals, the key components that enable C. rapunculi to recognize Campanula hosts, were detected in trace amounts in Geranium but could not be proved to occur in Malva. The visual floral cues of all species were particularly attractive for foraging-experienced bees. The high attractiveness of G. sanguineum and M. moschata flowers to C. rapunculi bees and the floral traits that are similar to the Campanula host plants can be a first step to the beginning of a host expansion or change which, however, rarely occurs in oligolectic bees.

Diet Breadth Affects Bacterial Identity but Not Diversity in the Pollen Provisions of Closely Related Polylectic and Oligolectic Bees

Mounting evidence suggests that microbes found in the pollen provisions of wild and solitary bees are important drivers of larval development. As these microbes are also known to be transmitted via the environment, most likely from flowers, the diet breadth of a bee may affect the diversity and identity of the microbes that occur in its pollen provisions. Here, we tested the hypothesis that, due to the importance of floral transmission of microbes, diet breadth affects pollen provision microbial community composition. We collected pollen provisions at four sites from the polylectic bee Osmia lignaria and the oligolectic bee Osmia ribifloris. We used high-throughput sequencing of the bacterial 16S rRNA gene to characterize the bacteria found in these provisions. We found minimal overlap in the specific bacterial variants in pollen provisions across the host species, even when the bees were constrained to foraging from the same flowers in cages at one site. Similarly, there was minimal overlap in the specific bacterial variants across sites, even within the same host species. Together, these findings highlight the importance of environmental transmission and host specific sorting influenced by diet breadth for microbes found in pollen provisions. Future studies addressing the functional consequences of this filtering, along with tests for differences between more species of oligoletic and polylectic bees will provide rich insights into the microbial ecology of solitary bees.

The cost of fidelity: foraging oligolectic bees gather huge amounts of pollen in a highly specialized cactus–pollinator association

Plant–pollinator interactions vary along a specialization–generalization continuum. Advances in understanding the evolutionary and ecological consequences of different degrees of specialization depend on precise data on plant–pollinator interdependency. We studied the association of Parodia neohorstii (Cactaceae) and its bee pollinators focusing on pollinator foraging behaviour, flower functioning, female and male reproductive success, and pollen fate. Parodia neohorstii showed synchronized flower opening and pollen presentation but discontinuous blooming. The apparently generalized flowers partition pollen through thigmonastic stamen movements that function as a mechanical filter against generalist bees by restricting access to the major pollen reservoir to bees that show flower handling ‘know-how’, thereby favouring the oligolectic bee Arhysosage cactorum. This pollinator adjusted its pollen foraging to flower opening, removed pollen hurriedly, and promoted maximal fruit and seed set, which was minimal in its absence. Estimates of pollen fate revealed that a huge amount of pollen flows to specialized pollinators (86.5%), and only 0.9% reaches conspecific stigmas. The specialized interaction between P. neohorstii and Arhysosage cactorum, both threatened species, is efficient but fragile. Any environmental modification that causes a mismatch between the partners is likely to result in reproductive failure.

Differential distribution of resources for females on a dioecious plant affects the small–scale distribution of male of an oligolectic bee

Females of the solitary digger bee Andrena florea Fabricius, 1793 (Hymenoptera, Andrenidae) nest in aggregations and collect pollen almost exclusively on dioecious plants of the genus Bryonia, making this species a good model to study the relationship between nest density, male density, male behaviour and female lecty. At a study site in the valley of the river Serio, in Italy, an aggregation of this bee showed low density of randomly distributed nests and was closely surrounded by B. dioica plants. Female nectar foraging and male feeding and mate–searching activity, confined to the host plants, peaked at similar hours across the day, while female pollen foraging peaked earlier. Males fed on plants of both sexes but seemed to perch waiting for females more frequently on male B. dioica leaves. Individual males more often visited only one of the male plants, for up to four days; here they did not interact aggressively with conspecifics, suggesting scramble competition in resource–based home ranges and not territoriality. These findings are preliminarily in accordance with the predicted resource–based rendez–vous sites at low nest density for oligolectic bees and the predicted occurrence of scramble competition in case of high male density. Additionally, males would maximize their mating opportunity by mainly perching on male plants, the only source of the most limited resource for females (pollen).

Diversity of Flower Visiting Insects in Dry Grasslands and Vineyards Close to the City of Vienna with Special Focus on Wild Bees.

Interactions between flower visiting insects and nectar resp. pollen producing plants belong to the most relevant in terrestrial ecosystems. Their diversity and dominance relationship are important indicators for the stability and functionality of ecosystems and belong to the high ranking ecosystem services. Potential pollinators should be strongly concerned especially regarding anthropogenic impacts on habitats. We studied the diversity and quantities of flower visiting insects with special focus on wild bees (Apiformes) in two locations near the city of Vienna (Austria). Insect sampling occurred in May until July 2015 every two weeks parallel to the vegetation surveys incl. records of the cover of flowering plants. In each location patches of semi-natural grassland as well as flowering strips within vineyards were investigated. We found a significant correlation between the number of insects or insect taxa (especially for Hymenoptera) and the current flower cover. In some cases flowering strips in vineyards harbor higher numbers of insects and higher diversity of bee species than the semi-natural grassland due to temporarily higher values of flower cover. However, grassland patches provide a much more constant supply with nectar producing plants replacing each other in their flowering phase during the season. In contrast, flowering strips are often dominated by one or a few short-lived sown plants, which is of advantage for some oligolectic bees specialized on Brassicaceae or Fabaceae. Flowering strips within organically farmed vineyards are more similar to semi-natural grassland regarding the diversity of flower visiting insects than to conventional farmed vineyards.

Supplementary note on the solitary bee fauna from the Suez Canal region of Egypt (Hymenoptera: Apoidea)

Previous surveys (2011–2013) of the bee fauna from the Suez Canal region, Egypt, recorded a total of 55 species. Those surveys did not include important floral species among the Asteraceae, a family known to be associated with various oligolectic bees. The aim of the present note is to report bees visiting four uncultivated species of Asteraceae that are common in the region during the Spring of 2014. Nine species of bees were recorded from these flowers, these increasing the number of species recorded from the Suez Canal region to 62. Some species, such as Daypoda sinuata Pérez (Melittidae) and Panurgus dentatus Friese (Andrenidae), are known oligoleges of Asteraceae.

Oligolectic bee species in Northern Europe (Hymenoptera, Apoidea)

Evolution of flower specialization in bees, the concepts of poly-, oligo- andmonolecty are reviewed. About 60 species recorded in the area of Finland and Sweden are regarded as oligolectic. The proportions of oligoleges among all pollen-collecting bee species are about 30 percent in alarge area of central and Northern Europe. The proportion is about 15 percent in the northern boreal area of Finland and Sweden, where the percentage of polylectic bumblebees is much greater than in more southern areas. Of the solitary bee species recorded in Finland and Sweden, 25 arc regarded as narrow oligoleges, of which 6 species collect pollen from Campanula and 5 from Salix. Eusocial Bombus consobrinus is regarded as a facultative narrow oligolege of Aconitum septentrionale and, apparently, this bee species is the only oligolege in northern Europe, whose distribution completely covers that of the pollen plant. The distribution limits of some narrow oligoleges (e.9. Eucera longicornis and Andrena hattorfiana) approximately follow certain frequencies of their principal pollen plants (lathyrus pratensis and Knautia, respectively). Of the oligolectic bee species in Finland, 32 occur on the lists of threatened species of England, southwestern Germany or Poland. Records of E. longicornis and A. hattorfiana from various periods are given as examples of the decline of oligolectic bees in Finland during recent decades.