Christian Walter Werner Pirk

Natural and within-farmland biodiversity enhances crop productivity.

Ongoing expansion of large-scale agriculture critically threatens natural habitats and the pollination services they offer. Creating patches with high plant diversity within farmland is commonly suggested as a measure to benefit pollinators. However, farmers rarely adopt such practice, instead removing naturally occurring plants (weeds). By combining pollinator exclusion experiments with analysis of honeybee behaviour and flower-visitation webs, we found that the presence of weeds allowed pollinators to persist within sunflower fields, maximizing the benefits of the remaining patches of natural habitat to productivity of this large-scale crop. Weed diversity increased flower visitor diversity, hence ameliorating the measured negative effects of isolation from natural habitat. Although honeybees were the most abundant visitors, diversity of flower visitors enhanced honeybee movement, being the main factor influencing productivity. Conservation of natural patches combined with promoting flowering plants within crops can maximize productivity and, therefore, reduce the need for cropland expansion, contributing towards sustainable agriculture.

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.

A worldwide survey of genome sequence variation provides insight into the evolutionary history of the honeybee Apis mellifera.

The honeybee Apis mellifera has major ecological and economic importance. We analyze patterns of genetic variation at 8.3 million SNPs, identified by sequencing 140 honeybee genomes from a worldwide sample of 14 populations at a combined total depth of 634×. These data provide insight into the evolutionary history and genetic basis of local adaptation in this species. We find evidence that population sizes have fluctuated greatly, mirroring historical fluctuations in climate, although contemporary populations have high genetic diversity, indicating the absence of domestication bottlenecks. Levels of genetic variation are strongly shaped by natural selection and are highly correlated with patterns of gene expression and DNA methylation. We identify genomic signatures of local adaptation, which are enriched in genes expressed in workers and in immune system– and sperm motility–related genes that might underlie geographic variation in reproduction, dispersal and disease resistance. This study provides a framework for future investigations into responses to pathogens and climate change in honeybees.

Adult honeybees (Apis mellifera L.) abandon hemocytic, but not phenoloxidase-based immunity

Hemocytes and the (prophenol-) phenoloxidase system constitute the immediate innate immune system in insects. These components of insect immunity are present at any post-embryonic life stage without previous infection. Differences between individuals and species in these immune parameters can reflect differences in infection risk, life expectancy, and biological function. In honeybees which show an age-related division of labor within the worker caste, previous studies demonstrated that foragers show a strongly reduced number of hemoctyes compared to the younger nurse bees. This loss of immune competence has been regarded advantageous with respect to an already high mortality rate due to foraging and to redistribution of energy costs at the colony level. Based on the idea that abandoning hemocytes in all adults would be a reasonably direct regulatory mechanism, we posed the hypothesis that abandoning hemocytic immunity is not restricted to worker honeybees. We tested our hypotheses by performing a comprehensive analysis of hemocyte number and phenoloxidase (PO)-activity levels in immunologically naive workers, queens, and drones. We found that in all three adult phenotypes hemocyte number is dramatically reduced in early adult life. In contrast, we found that the dynamics of PO-activity levels have sex and caste-specific characteristics. In workers, PO activity reached a plateau within the first week of adult life, and in queens enzyme levels continuously increased with age and reached levels twice as high as those found in workers. PO-activity levels slightly declined with age in drones. These data support our hypothesis, from which we infer that the previously reported reduction of hemocyte in foragers is not worker specific but represents a general phenomenon occurring in all honeybee adult phenotypes.

Statistical guidelines for Apis mellifera research

Summary In this article we provide guidelines on statistical design and analysis of data for all kinds of honey bee research. Guidelines and selection of different methods presented are, at least partly, based on experience. This article can be used: to identify the most suitable analysis for the type of data collected; to optimise ones experimental design based on the experimental factors to be investigated, samples to be analysed, and the type of data produced; to determine how, where, and when to sample bees from colonies; or just to inspire. Also included are guidelines on presentation and reporting of data, as well as where to find help and which types of software could be useful.

The importance of protein type and protein to carbohydrate ratio for survival and ovarian activation of caged honeybees (Apis mellifera scutellata)

Pollen is the natural source of protein for bees and it is commonly assumed that a high protein content in pollen is beneficial. Investigation of the optimal nutrient ratio for honeybees was prompted by our earlier study showing surprisingly high mortality in caged honeybees fed with the protein-rich pollen of Aloe greatheadii var davyana, although field bees experience optimal growth when feeding on this pollen. We tested the effect of different protein sources and different protein:carbohydrate (P:C) ratios on the survival and ovarian activation of caged bees. Bees fed casein showed consistently higher survival than those fed royal jelly or aloe pollen, regardless of P:C ratios. They survived longer on lower P:C ratios and longest on a pure carbohydrate diet. The greatest ovarian activation was recorded for bees fed royal jelly in a 1:3 P:C ratio, showing the superior quality of royal jelly for supporting development.ZusammenfassungDie Hauptnahrungsquellen für Honigbienen sind Nektar, der ihnenn hauptsächlich als Kohlenhydratquelle zur Energiegewinnung dient, und Pollen, der die hauptsächliche Proteinquelle darstellt und aus dem sie ausserdem Vitamine, Mineralien und Lipide gewinnen. Proteine sind vor allem für das rasche Wachstum der Larven und den Abschluss der Entwicklung erforderlich, und junge Arbeiterinnen füttern demzufolge die Larven mit Gelée royal, eingelagertem Pollen und Honig. Trotzdem sind unsere Kenntnisse gering über die Beziehungen der Makronährstoffe in der Diet der Honigbienen und deren physiologische Effekte. Wir untersuchten hier die Hypothese, ob eine Verringerung des Protein/Kohlenhydrat-Verhältnisses (P:C-Verhältnis), z.B. bedingt durch eine relative Anreicherung der Nahrung mit Kohlenhydraten, die Überlebensrate und die Ovaraktivität junger Arbeiterinnen erhöhen könnte. Dazu hielten wir jeweils 100 Arbeiteinnen in Käfigen in einem Brutschrank unter kontrollierten Bedingungen. Wir verabreichten ihnen jeweils eine von 11 zu testenden Diäten und untersuchten über einen Zeitraum von 14 Tagen die Überlebensraten. Danach wurden alle Bienen zur Erfassung der Ovarentwicklung abgetötet. Die Wichtigkeit des Kohlenhydratgehalts für das Überleben der Bienen ist unabhängig vom verabreichten Proteintyp (Abb. 1). Bienen, die auschschliesslich Proteine erhielten, zeigten eine deutlich verkürzte Lebensdauer, ganz im Gegensatz zu solchen, die ausschlieslich Sacharose erhielten. Der Unterschied zwischen diesen beiden Kontrolldiäten ist hochsignifikant (Tab. II). Innerhalb der Bienen, die den 14-täigen Untersuchungszeitraum überlebten. zeigten diejenigen, die Gelée royale in einen 1:3 P:C-Verhältnis erhalten hatten, den höchsten Grad der Ovaraktivierung (Abb. 2), mit einem mittleren Wert von Grad 3. Innerhalb der drei getesteten Proteinquellen zeigte Casein die besten Werte in Bezug auf die Überlebensraten, und zwar bei allen jeweiligen P:C-Verhältnissen. Da Gelée royale für alle essentiellen Aminosäuren über den Minimalanforderungen liegt und da Casein diese Anforderungen ebenfalls erfüllt, ist es unwahrscheinlich, dass die Aminosäurenzusammensetzung die niedrigere Mortalität bei Caseindiäten erklären kann. Die niedrigsten Úberlebensraten hatten wir für Pollen von A. greatheadii var davyana, der von Bienen gesammelt war. Dies mag daran liegen, dass sich bei den gekäfigten Bienen nicht abbaubare und/oder toxische Substsanzen im Darm ansammeln.Unsere Ergebnisse stehen in Einklang mit denen von Human et al. (2007), denenzufolge gekäfigte Bienen, die mit Aloepollen gefüttert worden waren, eine höhere Mortalität und eine geringere Ovaraktivität zeigten als Bienen, die Sonnenblumenpollen erhalten hatten. Dies könnte auf soziale Interaktionen innerhalb der gekäfigten Bienen zurückzuführen sein. Dominante Arbeiterinnen, die ihre Ovarien aktivieren, nutzen den “sozialen Nahrungsweg” und werden von untergeordneten Arbeiterinnen gefüttert, die Pollen verdauen und Gelée royale synthetisieren. Wenn diese untergeordneten Arbeiterinnen beispielsweise zu schnell aufgund der negativen Effekte von Pollen sterben, bricht die Nahrungskette zusammen und führt im Gesamtbild zu niedrigeren Überlebensund Ovaraktivierungsraten. In einer Feldsituation hingegen kann vermutlich der Proteinüberschuss in A. greatheadii var davyana Pollen gegenüber anderen Nahrungskompenenten durch das Vorhandensein ausreichenden Nektars verdünnt werden. Ausserdem sind unter Feldbedingungen stets genügend Arbeiterinnen vorhanden, um eventuelle Ausfälle in der Kette des “sozialen Nahrungswegs” zu kompensieren.

Is there a need for conservation of honeybees in Africa

Honeybees are native to Africa and Europe but have been spread worldwide as the basis for an apicultural industry. To date, large and diverse wild populations only remain in Africa. On this continent the beekeeping industry is relatively undeveloped and relies on trapping swarms from wild populations to constitute the managed stocks. Bee breeding is seldom practiced. The situation is therefore different from that of Europe or North America where wild or feral honeybees have almost disappeared and this distinction is important when assessing the conservation status of African honeybees. While African honeybees appear to be more resistant to major diseases, the history of honeybee populations worldwide suggests that their conservation is a necessity. After analyzing the threats to which honeybees are exposed in Africa, we argue that preventive conservation measures are required to maintain the present favorable situation and avoid the declines in populations experienced elsewhere.ZusammenfassungDie Beziehung zwischen Menschen und Honigbienen hat in Afrika verschiedene Formen: In vielen Ländern wird Honigjagd praktiziert; In einigen Ländern ist die traditionelle Bienenhaltung in Körben oder Klotzbeuten weitverbreitet während andere moderne Bienenhaltungstechnologie einsetzen. Der hauptsächliche kontextuelle Unterschied zu anderen Weltregionen, in denen die Honigbienen entweder heimisch sind oder eingeführt wurden, ist die bedeutende Population von freilebenden Bienen, auf denen Honigjagd und Ausbeutung basieren. Im Gegensatz zu Europa machen bewirtschaftete Völker nur einen kleinen Teil der Honigbienenpopulation aus (14–18 aus 310 Mio). Weiterhin basiert die Bienenhaltung in Afrika weitgehend auf dem Fang von wilden Schwärmen und es wird keine oder nur wenig Bienenzucht betrieben. Diese Unterschiede sind wichtig, wenn die Honigbienenpopulationen von den in anderen Teilen der Welt zu beobachtenden Abnahmen geschützt werden sollen. Für Afrika sollten daher besondere politische Maßnahmen entwickelt werden. Auf diesem Kontinent sind die Netzwerke, auf die sich Bienenhalter und die Bienenindustrie stützen können nur sehr schwach entwickelt, und es wurden nur wenige Untersuchungen über die Honigbienen durchgeführt. Es ist daher sehr schwer, genaue Informationen und Zahlen über den Gesundheitszustand der Honigbienenpopulationen zu erhalten und daraus abzuleiten, ob Schutzmaßnahmen notwendig sind. Angesichts der Größe der Wildpopulation und dem Fehlen von Berichten über Epidemien könnte man schließen, dass die Wildpopulation in Afrika nicht gefährdet ist und daher von den Imkern ausgebeutet werden kann. Obwohl afrikanische Honigbienen den meisten Krankheiten ausgesetzt sind, die weltweit Honigbienen schädigen und sie diesen widerstehen können, sind der Verlust von Habitaten und Bejagung zwei Faktoren, denen europäische Bienen in geringerem Ausmaß ausgesetzt sind (da freilebende Honigbienen praktisch nicht mehr vorkommen und die bewirtschafteten Völker in vom Menschen hergestellten Beuten leben). Diese und andere noch nicht identifizierte Faktoren (z. B. neue Krankheiten) können Honigbienen negativ beeinflussen und ihre Wirkung könnte unter Umständen zu Verlusten in ähnlichem Ausmaß führen, wie sie andernorts beobachtet werden. Um zu verhindern, dass etwas Ähnliches in Afrika passieren kann, schlagen wir die Schaffung und Verbesserung sowie eine effektive Inkraftsetzung von Regulationen vor, die auf eine Erhaltung der afrikanischen Honigbienen abzielen. Da Afrika das Ursprungsland von Apis mellifera darstellt und das einzige Weltgebiet, in dem eine große Wildpopulation erhalten ist, sind Anstrengungen zur Erhaltung nicht nur zum Erhalt von einzigartigen Populationen vonnöten, sondern auch, um das Funktionieren des Ökosystems und der landwirtschaftlichen Produktion sicherzustellen, die beide von den Bestäubungsleistungen der Honigbienen abhängig sind.

A survey of managed honey bee colony losses in the Republic of South Africa–2009 to 2011

Summary This study reports honey bee, Apis mellifera L., colony losses that occurred in South Africa over two consecutive years. The total losses were 29.6% (95% CI: 22.8–37.5) in 2009–2010 and 46.2% (95% CI: 37.3–55.0) in 2010–2011. Furthermore, the study shows that the capensss worker social parasite, a problem unique to southern Africa, is the main perceived cause, and could explain the significant differences in the number of losses between beekeepers using the subspecies A. m. scutellata and those using the subspecies A. m. capensis. In contrast to previous studies in North America and Europe, we find a significant negative effect of migratory beekeeping practices on the extent of colony losses. Migratory beekeepers lost on average more colonies (35.5% (95% CI 29.7–47.2)) than did stationary beekeepers (17.2% (95% CI 11.2–22.3)). This was especially pronounced when the beekeepers were migrating for the pollination of apples/cherries, eucalyptus, onions and/or sunflowers. The major beekeeper-perceived causes of mortality were small hive beetles, varroa mites, absconding (non-reproductive swarming), and chalkbrood disease. Those listing chalkbrood disease lost significantly fewer colonies than those who did not list chalkbrood. The exact mechanism for this difference is unknown, and may be related to other beekeeping practices that correlate with finding chalkbrood infections—namely more intensive inspection and management.

Honeybees and nectar nicotine: Deterrence and reduced survival versus potential health benefits

Secondary metabolites produced by plants for herbivore defence are often found in floral nectar, but their effect on the foraging behaviour and physiological performance of pollinators is largely unknown. Nicotine is highly toxic to most herbivores, and nicotine-based insecticides may contribute to current pollinator declines. We examined the effects of nectar nicotine on honeybee foraging choices and worker longevity. Free-flying honeybee (Apis mellifera scutellata) workers from six colonies were given a choice between multiple nicotine concentrations (0-1000 μM) in artificial nectar (0.15-0.63 M sucrose). The dose-dependent deterrent effect of nicotine was stronger in lower sugar concentrations, but even the highest nicotine concentrations did not completely repel honeybees, i.e., bees did not stop feeding on these diets. Nicotine in nectar acts as a partial repellent, which may keep pollinators moving between plants and enhance cross-pollination. In the second part of the study, newly emerged workers from 12 colonies were caged and fed one of four nicotine concentrations (0-300 μM) in 0.63 M sucrose for 21 days. Moderate (≤30 μM) nicotine concentrations had no significant detrimental effect, but high nicotine concentrations reduced the survival of caged workers and their nectar storage in the honey comb. In contrast, worker groups that survived poorly on sugar-only diets demonstrated increased survival on all nicotine diets. In the absence of alternative nectar sources, honeybees tolerate naturally occurring nectar nicotine concentrations; and low concentrations can even be beneficial to honeybees. However, high nicotine concentrations may have a detrimental effect on colony fitness.

Convergence of carbohydrate-biased intake targets in caged worker honeybees fed different protein sources

SUMMARY The nutritional needs of bees are supplied by nectar carbohydrates and by protein and other nutrients in pollen but little is known of how bees achieve nutritional balance. Using newly emerged caged worker honeybees (Apis mellifera scutellata), we investigated whether bees maintain their intake target when confined to pairs of imbalanced complementary diets varying in protein to carbohydrate (P:C) ratio. Diets were formulated using three protein sources [casein, royal jelly or Feed-Bee® (a natural pollen substitute)] and sucrose. Within each protein type, honeybees switched between complementary diets and converged on the same P:C intake target. However, this target differed between protein types: P:C ratios were 1:12, 1:14 and 1:11 on casein, royal jelly and Feed-Bee® diets, respectively. Except for an early peak in protein consumption on royal jelly diets, these strongly convergent ratios remained constant over the 14 day experiment. This is probably due to the absence of brood, reflected in relatively stable values measured for haemolymph protein concentration and hypopharyngeal gland activation in bees on Feed-Bee® diets. Performance of caged workers was also assessed in terms of survival and ovarian activation. Survival was highest on casein diets and lowest on Feed-Bee® diets but ovarian activation was highest on royal jelly diets and lowest on casein diets. This may be due to additional components in Feed-Bee® and royal jelly (e.g. fatty acids), which are needed to activate the ovaries but also reduce survival. Nutrient intake of broodless workers is directly related to their own physiological requirements, and the strong carbohydrate bias may reflect the high metabolic rate of honeybees even under resting conditions.