Pierre Rasmont

Climate change impacts on bumblebees converge across continents

Bucking the trend Responses to climate change have been observed across many species. There is a general trend for species to shift their ranges poleward or up in elevation. Not all species, however, can make such shifts, and these species might experience more rapid declines. Kerr et al. looked at data on bumblebees across North America and Europe over the past 110 years. Bumblebees have not shifted northward and are experiencing shrinking distributions in the southern ends of their range. Such failures to shift may be because of their origins in a cooler climate, and suggest an elevated susceptibility to rapid climate change. Science, this issue p. 177 Cool-adapted bumblebees are failing to shift their ranges in response to climate warming. For many species, geographical ranges are expanding toward the poles in response to climate change, while remaining stable along range edges nearest the equator. Using long-term observations across Europe and North America over 110 years, we tested for climate change–related range shifts in bumblebee species across the full extents of their latitudinal and thermal limits and movements along elevation gradients. We found cross-continentally consistent trends in failures to track warming through time at species’ northern range limits, range losses from southern range limits, and shifts to higher elevations among southern species. These effects are independent of changing land uses or pesticide applications and underscore the need to test for climate impacts at both leading and trailing latitudinal and thermal limits for species.

Species richness declines and biotic homogenisation have slowed down for NW-European pollinators and plants

Concern about biodiversity loss has led to increased public investment in conservation. Whereas there is a widespread perception that such initiatives have been unsuccessful, there are few quantitative tests of this perception. Here, we evaluate whether rates of biodiversity change have altered in recent decades in three European countries (Great Britain, Netherlands and Belgium) for plants and flower visiting insects. We compared four 20-year periods, comparing periods of rapid land-use intensification and natural habitat loss (1930–1990) with a period of increased conservation investment (post-1990). We found that extensive species richness loss and biotic homogenisation occurred before 1990, whereas these negative trends became substantially less accentuated during recent decades, being partially reversed for certain taxa (e.g. bees in Great Britain and Netherlands). These results highlight the potential to maintain or even restore current species assemblages (which despite past extinctions are still of great conservation value), at least in regions where large-scale land-use intensification and natural habitat loss has ceased.

A simplified subgeneric classification of the bumblebees (genus Bombus)

A system of subgenera has been widely used for nearly a century to communicate ideas of relationships among bumblebee species. However, with 38 subgenera in recent lists for about 250 species, the system has come to be seen as too complicated. In this paper we suggest four criteria to guide the process of simplifying the subgeneric system, so that ideally subgenera should become: (1) monophyletic; (2) fewer; (3) diagnosable from morphology; and (4) names for important behavioural and ecological groups. Using a new strongly-supported estimate of phylogeny for almost all bumblebee species, we apply these criteria to reduce the system to 15 subgenera, and we assess the consequences. Ten new subgeneric synonyms are recognised. Keys to identify adult bumblebees to the simplified subgenera are provided for both sexes.ZusammenfassungHummeln sind farblich sehr variabel, morphologisch ansonsten aber relativ einheitlich. Um die Variation sinnvoll zu ordnen, besteht eine lange Tradition die Arten in Untergattungen zusammenzufassen und sich hierbei zunächst auf die Färbung, dann auf die Morphologie und neuerdings auch auf DNA Sequenzen zu stützen. Allerdings wurde bei 38 Unterarten in den derzeitigen Listungen die Notwendigkeit einer Vereinfachung des Systems gesehen. Wir besprechen die weiterhin bestehende Nützlichkeit des Systems von Untergattungen und erörtern vier mögliche als Leitlinie für Änderungen nutzbare Kriterien. Wir schlagen vor, dass Untergattungen (1) monophyletisch, (2) weniger, (3) aus der Morphologie erkennbar werden sollten und (4) zur Namensgebung wichtiger verhaltensmäßiger oder ökologischer Gruppen dienlich sein sollten. Unter Nutzung einer fast alle Hummeln einschließenden gut fundierten Abschätzung der Phylogenie besprechen wir Konflikte in der Nutzung dieser Kriterien und schlagen ein vereinfachtes System aus 15 Untergattungen vor, in der 10 neue Untergattungssynonyme anerkannt werden. Wir fanden es leicht, monophyletische Subgenera zu erkennen und ihre Anzahl zu reduzieren. Dagegen wurde es mit zunehmender Artenzahl immer schwieriger, Untergattungen zu definieren, die sowohl morphologisch leicht zu unterscheiden waren als auch einige der oft als besonders wichtig angesehenen verhaltensmässigen und ökologischen Eigenschaften teilen. Dies war deshalb der Fall, da entsprechend unserer vorläufigen Analyse einzelne Ausprägungen dieser Eigenschaften nicht ausschließlich von allen Arten einer morphologischen Gruppe geteilt werden.

Born in an Alien Nest : How Do Social Parasite Male Offspring Escape from Host Aggression?

Social parasites exploit the colony resources of social insects. Some of them exploit the host colony as a food resource or as a shelter whereas other species also exploit the brood care behavior of their social host. Some of these species have even lost the worker caste and rely completely on the hosts worker force to rear their offspring. To avoid host defenses and bypass their recognition code, these social parasites have developed several sophisticated chemical infiltration strategies. These infiltration strategies have been highly studied in several hymenopterans. Once a social parasite has successfully entered a host nest and integrated its social system, its emerging offspring still face the same challenge of avoiding host recognition. However, the strategy used by the offspring to survive within the host nest without being killed is still poorly documented. In cuckoo bumblebees, the parasite males completely lack the morphological and chemical adaptations to social parasitism that the females possess. Moreover, young parasite males exhibit an early production of species-specific cephalic secretions, used as sexual pheromones. Host workers might thus be able to recognize them. Here we used a bumblebee host-social parasite system to test the hypothesis that social parasite male offspring exhibit a chemical defense strategy to escape from host aggression during their intranidal life. Using behavioral assays, we showed that extracts from the heads of young cuckoo bumblebee males contain a repellent odor that prevents parasite males from being attacked by host workers. We also show that social parasitism reduces host worker aggressiveness and helps parasite offspring acceptance.

Developing European Conservation and Mitigation Tools for Pollination Services: Approaches of the STEP (Status and Trends of European Pollinators) Project

Summary Pollinating insects form a key component of European biodiversity, and provide a vital ecosystem service to crops and wild plants. There is growing evidence of declines in both wild and domesticated pollinators, and parallel declines in plants relying upon them. The STEP project (Status and Trends of European Pollinators, 2010–2015, www.step-project.net) is documenting critical elements in the nature and extent of these declines, examining key functional traits associated with pollination deficits, and developing a Red List for some European pollinator groups. Together these activities are laying the groundwork for future pollinator monitoring programmes. STEP is also assessing the relative importance of potential drivers of pollinator declines, including climate change, habitat loss and fragmentation, agrochemicals, pathogens, alien species, light pollution, and their interactions. We are measuring the ecological and economic impacts of declining pollinator services and floral resources, including effects on wild plant populations, crop production and human nutrition. STEP is reviewing existing and potential mitigation options, and providing novel tests of their effectiveness across Europe. Our work is building upon existing and newly developed datasets and models, complemented by spatially-replicated campaigns of field research to fill gaps in current knowledge. Findings are being integrated into a policy-relevant framework to create evidence-based decision support tools. STEP is establishing communication links to a wide range of stakeholders across Europe and beyond, including policy makers, beekeepers, farmers, academics and the general public. Taken together, the STEP research programme aims to improve our understanding of the nature, causes, consequences and potential mitigation of declines in pollination services at local, national, continental and global scales.

How Does Pollen Chemistry Impact Development and Feeding Behaviour of Polylectic Bees

Larvae and imagos of bees rely exclusively on floral rewards as a food source but host-plant range can vary greatly among bee species. While oligolectic species forage on pollen from a single family of host plants, polylectic bees, such as bumblebees, collect pollen from many families of plants. These polylectic species contend with interspecific variability in essential nutrients of their host-plants but we have only a limited understanding of the way in which chemicals and chemical combinations influence bee development and feeding behaviour. In this paper, we investigated five different pollen diets (Calluna vulgaris, Cistus sp., Cytisus scoparius, Salix caprea and Sorbus aucuparia) to determine how their chemical content affected bumblebee colony development and pollen/syrup collection. Three compounds were used to characterise pollen content: polypeptides, amino acids and sterols. Several parameters were used to determine the impact of diet on micro-colonies: (i) Number and weight of larvae (total and mean weight of larvae), (ii) weight of pollen collected, (iii) pollen efficacy (total weight of larvae divided by weight of the pollen collected) and (iv) syrup collection. Our results show that pollen collection is similar regardless of chemical variation in pollen diet while syrup collection is variable. Micro-colonies fed on S. aucuparia and C. scoparius pollen produced larger larvae (i.e. better mates and winter survivors) and fed less on nectar compared to the other diets. Pollen from both of these species contains 24-methylenecholesterol and high concentrations of polypeptides/total amino acids. This pollen nutritional “theme” seems therefore to promote worker reproduction in B. terrestris micro-colonies and could be linked to high fitness for queenright colonies. As workers are able to selectively forage on pollen of high chemical quality, plants may be evolutionarily selected for their pollen content, which might attract and increase the degree of fidelity of generalist pollinators, such as bumblebees.

An overview of the Bombus terrestris (L. 1758) subspecies (Hymenoptera: Apidae)

Abstract Bombus terrestris is one of the most abundant bumblebee species in the West-Palaearctic. Its widespread domestication results in the movement of many colonies. The aim of this paper is to describe the 9 subspecies currently recognised and to list some of their most obvious characteristics. Bombus terrestris is not declining anywhere, on the contrary, its synanthropic spread through domestication may be expected. However, its autumn and winter populations rely on a restricted choice of flowers so they may be threatened locally by scrub clearance and the destruction of their favourite autumnal flowers.

Landmark based geometric morphometric analysis of wing shape in Sibiricobombus Vogt (Hymenoptera: Apidae: Bombus Latreille)

Summary B. (Sibiricobombus) niveatus and B. (Sibiricobombus) vorticosus are analyzed and compared with selected species of the subgenera Melanobombus and Mendacibombus. Different geometric morphometric methods based on wings landmark data show that there are no morphological differences between B. niveatus and B. vorticosus. These results support the hypothesis that B. niveatus and B. vorticosus should be regarded as conspecific. On the other hand, the wing shapes show significant differences among the bumblebee species and subgenera that are coherent with their specific and subgeneric status. This approach may help future studies not only by contributing towards solving problems in systematics but also in understanding the flight mechanism of bumblebees. It also supports studies on the evolution of crossvein structure and on aerodynamics of different wing shapes in insects.

Analysis of Pollen and Nectar of Arbutus unedo as a Food Source for Bombus terrestris (Hymenoptera : Apidae)

Abstract The mineral, total amino acid, and sterol compositions of pollen collected by Apis mellifera L. were compared with the pollen of a plant consumed by Bombus terrestris (L.): Arbutus unedo L. This plant provides the predominant food resource for the main autumn generation of B. terrestris in southern France. Honey bees also forage on this plant, although only for nectar. The mineral composition of 30 pollen samples collected by honey bees is close to the presently known requirements of A. mellifera, except for Cu and Mn, which are substantially lower. The total amino acid mean composition of a set of 54 pollen samples fits the basic requirements of honey bees except for valine, isoleucine, and methionine, which are present in lower concentrations in all the samples. For pollen of A. unedo, the amino acid balance is not very different from that of the survey. The main sterolic component in pollen of A. unedo, β-sitosterol, is known to have antifeedant effects on A. mellifera. Honey bees cannot dealkylate C29 sterols like β-sitosterol or δ5-avenasterol to obtain C27 cholesterol and ecdysteroids. Because these phytosterols as well as cholesterol are nearly absent from pollen of A. unedo, the metabolic capabilities of Apis seem unadapted to this plant. On the contrary, pollen of A. unedo is freely consumed by B. terrestris, which develops huge autumn populations solely on this food. These data indicate that the sterolic metabolisms of B. terrestris and A. mellifera differ, allowing separation in foraging activity.

Phylogeny and host-plant evolution in Melittidae s.l. (Hymenoptera: Apoidea)

Bees and the angiosperms they pollinate have developed intimate and often complex interactions over the past 100 million years. As in other insect-plant interactions, host-plant specificity is variable among taxa. While many solitary bee species display an obvious preference for a narrow spectrum of host-plants (oligolecty), others regularly visit a diversified array of pollen hosts (polylecty). Few studies have examined the patterns of host-plant associations in bees using well-resolved phylogenies at the species level combined with accurate and quantitative data on host-plant preferences. In this study, we examined the evolution of bee-plant relationships in several genera of specialist (oligolectic) bees. We used the Melittidae s.l. as a model taxon by mapping the preferred pollen hosts onto species-level phylogenies to investigate the frequency and pattern of host-plant switching. Our results suggest that host-plant associations are maintained over time in many lineages, but that host switches to unrelated plant families are also common. We find some evidence that host-switches occur more frequently to morphologically similar, rather than closely-related, host-plants suggesting that floral morphology plays a key role in host-plant evolution in bees.ZusammenfassungWie viele Gruppen pflanzenfressender Insekten zeigen auch Bienen Variation sowohl in der Wirtspflanzenwahl als auch in der Breite ihrer Wirtspflanzen. Einige Bienen zeigen eine hohe Spezifität in der Blütenwahl (Oligolektie; viele Solitärbienen), während andere ein weites Spektrum in der Blütenwahl aufweisen (Polylektie; die meisten eusozialen Bienen). Nur wenige frühere Studien haben die Muster der Wirtspflanzenwahl in Beziehung zu einer gut aufgelösten Phylogenie auf dem Artniveau untersucht.Wir untersuchten die Vererbung der Wirtspflanzenwahl über ihre evolutionäre Geschichte bei fünf Gattungen von spezialisierten Bienen innerhalb der Melittidae s.l. (Tab. II–V, Capicola, Dasypoda, Hesperapis, Macropis und Melitta). Wir kartierten die bevorzugten Pollenwirte über den Phylogenien auf dem Artniveau (Abb. 2–6). Wir versuchten insbesondere zu ermitteln, ob (i) Verschiebungen der Wirtspflanzen in diesen Kladen spezialisierter Bienen häufig sind, (ii) ob Wirtspflanzenverschiebungen zu entfernt verwandten Wirten vorkommen, (iii) ob Wirtspflanzenverschiebungen mit der Entstehung besonderer morphologischer Anpassungen einhergehen, und (iv) ob die Wirtspflanzenspezialisierung in diesen Gattungen als ursprünglich oder als abgeleitet angesehen werden kann.Wir zeigen, dass nahverwandte Arten in den meisten Fällen ähnliche Wirtspflanzen aufsuchen. Allerdings beobachteten wir in vier der fünf Gattungen Verschiebungen zu nichtverwandten Wirtspflanzen (mit Macropis als der einzigen Ausnahme). Die meisten Wechsel beinhalteten Umstellung von einer Wirtspflanzenfamilie zu einer anderen, nicht verwandten Wirtsfamilie, mit wenig Änderung der Auswahlbreite. Wechsel der Auswahlbreite, wenn sie beobachtet wurden, fanden hauptsächlich von Oligolektie zu Polylektie statt. Wirtspflanzenspezifität erscheint daher bei den melittiden Bienen ein ursprüngliches Verhalten zu sein. In mehreren anderen Bienenfamilien sind die basalen Gruppen ebenfalls oligolektisch (z. B. Lithurginae, Panurginae und Rophitinae). Dies legt den Schluss nahe, dass der ursprüngliche Zustand der Bienen oligolektisch war.