Rodolfo Jaffé

Biodiversity, conservation and current threats to European honeybees

Europe harbours several endemic honeybee (Apis mellifera) subspecies. Yet the distribution of these subspecies is nowadays also much influenced by beekeeping activities. Large scale migratory beekeeping and trade in queens, coupled with the promiscuous mating system of honeybees, have exposed native European honeybees to increasing introgressive hybridization with managed non-native subspecies, which may lead to the loss of valuable combinations of traits shaped by natural selection. Other threats to European honeybees are factors that have caused a progressive decline in A. mellifera throughout the world in recent years, leading to large economic losses and jeopardizing ecosystem functioning. We review the biodiversity of European honeybees and summarize the management and conservation strategies employed by different countries. A comprehensive picture of the beekeeping industry in Europe is also provided. Finally we evaluate the potential threats affecting the biodiversity of European honeybee populations and provide some perspectives for future research.ZusammenfassungDie Unterarten der Honigbienen wurden sowohl mit morphologischen (Box 1) als auch mit molekulargenetischen (Box 2 und 3) Methoden untersucht. Die in Europa vorkommenden elf Unterarten (Abb. 1) werden in vier evolutiven Abstammungslinien eingeteilt. In den entsprechenden Verbreitungsgebieten sind die dazugehörenden Unterarten unterschiedlichen Klima- und Habitatsbedingungen sowie anthropogenen Einflüssen ausgesetzt. Unser erstes Ziel ist es, die Biodiversität der europäischen Honigbienen zu beschreiben und die Strategien zum Schutz der Honigbienen in den einzelnen Ländern zusammenzufassen. Hybridisierungsprozesse wurden vor allem auf der iberischen, italienischen und der Balkan-Halbinsel festgestellt, wohingegen natürliche (aufgrund von Genfluss durch die Mehrfachpaarung der Königin) und durch imkerliche Aktivitäten ausgelöste (durch die Einfuhr von Honigbienen-Unterarten außerhalb ihres natürlichen Verbreitungsgebietes) genetische Introgression in Zentral- und Osteuropa sowie auf Mittelmeerinseln beobachtet wurden. Verschiedene Naturschutzprogramme wurden auf europäischen Inseln (Dänemark, Spanien) und seit kurzem auch in anderen europäischen Ländern (Frankreich, Norwegen, Slowenien und Österreich) etabliert. Für einen sinnvollen Honigbienenschutz muss aber der Status der imkerlich gehaltenen Honigbienenpopulation in den jeweiligen Ländern mit berücksichtigt werden. Daher müssen zunächst detaillierte Informationen zur Imkerei in den einzelnen Ländern gesammelt werden, bevor zukünftige Naturschutzprogramme entwickelt werden (Abb. 2 und Tab. I in „supplementary data“). Auf dieser Grundlage werden zwei Hauptansätze für zukünftige Naturschutzrichtlinien vorgeschlagen: Beschränkung der Einfuhr von „überlegenen“ Unterarten in Gebiete, die bereits von nativen Honigbienenpopulationen besetzt sind sowie die Aufrechterhaltung der genetischen Diversität in natürlichen Honigbienenpopulationen. Immer mehr Faktoren wie veränderte Landnutzung, die Verbreitung von Krankheitserregern und Parasiten, der Einsatz von Pestiziden und Herbiziden (Tab. I) bedrohen die Honigbienen in Europa und gefährden damit auch die Funktion des Ökosystems durch eine unzureichende Bestäubung von Wild- und Kulturpflanzen.Das vor kurzem aufgeschlüsselte Honigbienen-Genom bietet nun aber neue Möglichkeiten, auf molekularer Ebene die Genetik, Physiologie und das Verhalten der Honigbienen zu untersuchen. Molekulare Marker wie SNPs („Single Nucleotide Polymorphisms“) und Mikrosatelliten ermöglichen neue Einblicke in die Populationsstruktur der Honigbienen und die Analyse des Honigbienen-Proteoms wird uns zusätzlich Informationen über die Struktur, Funktion und Wechselwirkungen der von den jeweiligen Genen produzierten Proteine geben.Eine abschließende Überlegung ist, dass der Honigbienenschutz eng mit der Aufrechterhaltung der Imkerei verbunden ist, die als zukunftsträchtiger Bestandteil der landwirtschaftlichen Praxis auch für die junge Generation attraktiv sein sollte. Für eine nachhaltige Unterstützung der Imkerei sollten die Berufsausbildung verbessert, moderne Betriebsweisen eingeführt, angewandte Forschung zur Bienenbiologie, Genetik und Krankheitsbekämpfung durchgeführt sowie sinnvolle Richtlinien zum Schutz wertvoller Ökosysteme umgesetzt werden.

Miscellaneous standard methods for Apis mellifera research

Summary A variety of methods are used in honey bee research and differ depending on the level at which the research is conducted. On an individual level, the handling of individual honey bees, including the queen, larvae and pupae are required. There are different methods for the immobilising, killing and storing as well as determining individual weight of bees. The precise timing of developmental stages is also an important aspect of sampling individuals for experiments. In order to investigate and manipulate functional processes in honey bees, e.g. memory formation and retrieval and gene expression, microinjection is often used. A method that is used by both researchers and beekeepers is the marking of queens that serves not only to help to locate her during her life, but also enables the dating of queens. Creating multiple queen colonies allows the beekeeper to maintain spare queens, increase brood production or ask questions related to reproduction. On colony level, very useful techniques are the measurement of intra hive mortality using dead bee traps, weighing of full hives, collecting pollen and nectar, and digital monitoring of brood development via location recognition. At the population level, estimation of population density is essential to evaluate the health status and using beelines help to locate wild colonies. These methods, described in this paper, are especially valuable when investigating the effects of pesticide applications, environmental pollution and diseases on colony survival.

Estimating the Density of Honeybee Colonies across Their Natural Range to Fill the Gap in Pollinator Decline Censuses

Although pollinator declines are a global biodiversity threat, the demography of the western honeybee (Apis mellifera) has not been considered by conservationists because it is biased by the activity of beekeepers. To fill this gap in pollinator decline censuses and to provide a broad picture of the current status of honeybees across their natural range, we used microsatellite genetic markers to estimate colony densities and genetic diversity at different locations in Europe, Africa, and central Asia that had different patterns of land use. Genetic diversity and colony densities were highest in South Africa and lowest in Northern Europe and were correlated with mean annual temperature. Confounding factors not related to climate, however, are also likely to influence genetic diversity and colony densities in honeybee populations. Land use showed a significantly negative influence over genetic diversity and the density of honeybee colonies over all sampling locations. In Europe honeybees sampled in nature reserves had genetic diversity and colony densities similar to those sampled in agricultural landscapes, which suggests that the former are not wild but may have come from managed hives. Other results also support this idea: putative wild bees were rare in our European samples, and the mean estimated density of honeybee colonies on the continent closely resembled the reported mean number of managed hives. Current densities of European honeybee populations are in the same range as those found in the adverse climatic conditions of the Kalahari and Saharan deserts, which suggests that beekeeping activities do not compensate for the loss of wild colonies. Our findings highlight the importance of reconsidering the conservation status of honeybees in Europe and of regarding beekeeping not only as a profitable business for producing honey, but also as an essential component of biodiversity conservation.

Worker caste determination in the army ant Eciton burchellii

Elaborate division of labour has contributed significantly to the ecological success of social insects. Division of labour is achieved either by behavioural task specialization or by morphological specialization of colony members. In physical caste systems, the diet and rearing environment of developing larvae is known to determine the phenotype of adult individuals, but recent studies have shown that genetic components also contribute to the determination of worker caste. One of the most extreme cases of worker caste differentiation occurs in the army ant genus Eciton, where queens mate with many males and colonies are therefore composed of numerous full-sister subfamilies. This high intracolonial genetic diversity, in combination with the extreme caste polymorphism, provides an excellent test system for studying the extent to which caste determination is genetically controlled. Here we show that genetic effects contribute significantly to worker caste fate in Eciton burchellii. We conclude that the combination of polyandry and genetic variation for caste determination may have facilitated the evolution of worker caste diversity in some lineages of social insects.

Dynamic microbiome evolution in social bees

Honey bees, bumble bees, and stingless bees have related gut microbial communities that are shaped by host evolutionary history. The highly social (eusocial) corbiculate bees, comprising the honey bees, bumble bees, and stingless bees, are ubiquitous insect pollinators that fulfill critical roles in ecosystem services and human agriculture. Here, we conduct wide sampling across the phylogeny of these corbiculate bees and reveal a dynamic evolutionary history behind their microbiota, marked by multiple gains and losses of gut associates, the presence of generalist as well as host-specific strains, and patterns of diversification driven, in part, by host ecology (for example, colony size). Across four continents, we found that different host species have distinct gut communities, largely independent of geography or sympatry. Nonetheless, their microbiota has a shared heritage: The emergence of the eusocial corbiculate bees from solitary ancestors appears to coincide with the acquisition of five core gut bacterial lineages, supporting the hypothesis that host sociality facilitates the development and maintenance of specialized microbiomes.

Bees for development: Brazilian survey reveals how to optimize stingless beekeeping.

Stingless bees are an important asset to assure plant biodiversity in many natural ecosystems, and fulfill the growing agricultural demand for pollination. However, across developing countries stingless beekeeping remains an essentially informal activity, technical knowledge is scarce, and management practices lack standardization. Here we profited from the large diversity of stingless beekeepers found in Brazil to assess the impact of particular management practices on productivity and economic revenues from the commercialization of stingless bee products. Our study represents the first large-scale effort aiming at optimizing stingless beekeeping for honey/colony production based on quantitative data. Survey data from 251 beekeepers scattered across 20 Brazilian States revealed the influence of specific management practices and other confounding factors over productivity and income indicators. Specifically, our results highlight the importance of teaching beekeepers how to inspect and feed their colonies, how to multiply them and keep track of genetic lineages, how to harvest and preserve the honey, how to use vinegar traps to control infestation by parasitic flies, and how to add value by labeling honey containers. Furthermore, beekeeping experience and the network of known beekeepers were found to be key factors influencing productivity and income. Our work provides clear guidelines to optimize stingless beekeeping and help transform the activity into a powerful tool for sustainable development.

Temporal variation in the genetic structure of a drone congregation area: an insight into the population dynamics of wild African honeybees (Apis mellifera scutellata)

The mating system of the honeybee (Apis mellifera) has been regarded as one of the most panmictic in the animal kingdom, with thousands of males aggregating in drone congregation areas (DCAs) that virgin queens visit to mate with tens of partners. Although males from many colonies gather at such congregations, the temporal changes in the colonies contributing drones remain unknown. Yet, changes in the DCAs’ genetic structure will ultimately determine population gene flow and effective population size. By repeatedly sampling drones from an African DCA over a period of 3 years, we studied the temporal changes in the genetic structure of a wild honeybee population. Using three sets of tightly linked microsatellite markers, we were able to reconstruct individual queen genotypes with a high accuracy, follow them through time and estimate their rate of replacement. The number of queens contributing drones to the DCA varied from 12 to 72 and was correlated with temperature and rainfall. We found that more than 80% of these queens were replaced by mostly unrelated ones in successive eight months sampling intervals, which resulted in a clear temporal genetic differentiation of the DCA. Our results suggest that the frequent long‐range migration of colonies without nest‐site fidelity is the main driver of this high queen turnover. DCAs of African honeybees should thus be regarded as extremely dynamic systems which together with migration boost the effective population size and maintain a high genetic diversity in the population.

Deformed wing virus and drone mating flights in the honey bee (Apis mellifera): implications for sexual transmission of a major honey bee virus

Deformed wing virus (DWV) represents an ideal model to study the interaction between mode of transmission and virulence in honey bees since it exhibits both horizontal and vertical transmissions. However, it is not yet clear if venereal–vertical transmission represents a regular mode of transmission for this virus in natural honey bee populations. Here, we provide clear evidence for the occurrence of high DWV titres in the endophallus of sexually mature drones collected from drone congregation areas (DCAs). Furthermore, the endophallus DWV titres of drones collected at their maternal hives were no different from drones collected at nearby DCAs, suggesting that high-titre DWV infection of the endophallus does not hinder the ability of drones to reach the mating area. The results are discussed within the context of the dispersal of DWV between colonies and the definition of DWV virulence with respect to the transmission route and the types of tissues infected.

Mating flights select for symmetry in honeybee drones (Apis mellifera)

Males of the honeybee (Apis mellifera) fly to specific drone congregation areas (DCAs), which virgin queens visit in order to mate. From the thousands of drones that are reared in a single colony, only very few succeed in copulating with a queen, and therefore, a strong selection is expected to act on adult drones during their mating flights. In consequence, the gathering of drones at DCAs may serve as an indirect mate selection mechanism, assuring that queens only mate with those individuals having a better flight ability and a higher responsiveness to the queen’s visual and chemical cues. Here, we tested this idea relying on wing fluctuating asymmetry (FA) as a measure of phenotypic quality. By recapturing marked drones at a natural DCA and comparing their size and FA with a control sample of drones collected at their maternal hives, we were able to detect any selection on wing size and wing FA occurring during the mating flights. Although we found no solid evidence for selection on wing size, wing FA was found to be significantly lower in the drones collected at the DCA than in those collected at the hives. Our results demonstrate the action of selection during drone mating flights for the first time, showing that developmental stability can influence the mating ability of honeybee drones. We therefore conclude that selection during honeybee drone mating flights may confer some fitness advantages to the queens.

Conserving genetic diversity in the honeybee: comments on Harpur et al. (2012).

The article by Harpur et al. (2012) ‘Management increases genetic diversity of honey bees via admixture’ concludes that ‘…honey bees do not suffer from reduced genetic diversity caused by management and, consequently, that reduced genetic diversity is probably not contributing to declines of managed Apis mellifera populations’. In the light of current honeybee and beekeeping declines and their consequences for honeybee conservation and the pollination services they provide, we would like to express our concern about the conclusions drawn from the results of Harpur et al. (2012). While many honeybee management practices do not imply admixture, we are convinced that the large‐scale genetic homogenization of admixed populations could drive the loss of valuable local adaptations. We also point out that the authors did not account for the extensive gene flow that occurs between managed and wild/feral honeybee populations and raise concerns about the data set used. Finally, we caution against underestimating the importance of genetic diversity for honeybee colonies and highlight the importance of promoting the use of endemic honeybee subspecies in apiculture.