Drone and Worker Brood Microclimates Are Regulated Differentially in Honey Bees,Apis mellifera

Background

Honey bee (Apis mellifera) drones and workers show differences in morphology, physiology, and behavior. Because the functions of drones are more related to colony reproduction, and those of workers relate to both survival and reproduction, we hypothesize that the microclimate for worker brood is more precisely regulated than that of drone brood.

Methodology/Principal Findings

We assessed temperature and relative humidity (RH) inside honey bee colonies for both drone and worker brood throughout the three-stage development period, using digital HOBO^® Data Loggers. The major findings of this study are that 1) both drone and worker castes show the highest temperature for eggs, followed by larvae and then pupae; 2) temperature in drones are maintained at higher precision (smaller variance) in drone eggs and larvae, but at a lower precision in pupae than the corresponding stages of workers; 3) RH regulation showed higher variance in drone than workers across all brood stages; and 4) RH regulation seems largely due to regulation by workers, as the contribution from empty honey combs are much smaller compared to that from adult workers.

Conclusions/Significance

We conclude that honey bee colonies maintain both temperature and humidity actively; that the microclimate for sealed drone brood is less precisely regulated than worker brood; and that combs with honey contribute very little to the increase of RH in honey bee colonies. These findings increase our understanding of microclimate regulation in honey bees and may have implications for beekeeping practices.     

Selection for outbreeding in Varroa parasitising resistant honey bee (Apis mellifera) colonies

Parasitism is expected to select for counter‐adaptations in the host: driving a coevolutionary arms race. However, human interference between honey bees (Apis mellifera) and Varroa mites removes the effect of natural selection and restricts the evolution of host counter‐adaptations. With full‐sibling mating common among Varroa, this can rapidly select for virulent, highly inbred, Varroa populations. We investigated how the evolution of host resistance could affect the infesting population of Varroa mites. We screened a Varroa‐resistant honey bee population near Toulouse, France, for a Varroa resistance trait: the inhibition of Varroa's reproduction in drone pupae. We then genotyped Varroa which had co‐infested a cell using microsatellites. Across all resistant honey bee colonies, Varroa's reproductive success was significantly higher in co‐infested cells but the distribution of Varroa between singly and multiply infested cells was not different from random. While there was a trend for increased reproductive success when Varroa of differing haplotypes co‐infested a cell, this was not significant. This suggests local mate competition, through the presence of another Varroa foundress in a pupal cell, may be enough to help Varroa overcome host resistance traits; with a critical mass of infesting Varroa overwhelming host resistance. However, the fitness trade‐offs associated with preferentially co‐infesting cells may be too high for Varroa to evolve a mechanism to identify already‐infested cells. The increased reproductive success of Varroa when co‐infesting resistant pupal cells may act as a release valve on the selective pressure for the evolution of counter resistance traits: helping to maintain a stable host–parasite relationship.     

Varroa Mite Infestations in Elevated Honey Bee Brood Cells: Effects of Context and Caste

The Varroa mite infestation level of honey bee, Apis mellifera, worker larvae reared in individual raised cells was 6-fold higher than in the adjacent six cells surrounding them; this differential infestation rate is similar to published values of higher mite infestations of drone cells compared to worker cells. Infestation levels in control cells were the same as in the surrounding cells. In contrast to infestation of these individually raised cells, Varroa mites invaded worker larvae in raised cells along the perimeter of a patch of raised cells (10 by 21 rows) 2.5 times more often than surrounding unraised cells, and similarly ca. 2.5 times more often than in the remaining raised cells (interior) of this patch. In similarly prepared frames of drone comb, Varroa mites invaded individually raised drone cells 3.3-fold more often than the adjacent surrounding cells and control cells. On the other hand, Varroa mites infested drone larvae in the interior of the raised-patch area as often as drones in raised cells along the perimeter of the raised-patch, and this rate was ca. 2.5-fold higher than for drone larvae in unraised cells surrounding the raised-patch and drone larvae in control cells. The higher levels of infestation of raised cells did not come at the expense of the surrounding cells, i.e., the infestation levels of the adjacent surrounding cells were the same as in control cells. For worker larvae, the increased number of mites invading individual raised cells and edge cells of the raised patch were proportional to the number of surrounding nonraised cells. The relationship between raised cell-edges, observations of mite walking behavior on comb surfaces, and larval-to-cell-rim distances are discussed in relation to their possible roles in eliciting mite invasion of honey bee larval cells and contrasted to the putative role of kairomones in larval-host location.     

A gene for resistance to the Varroa mite (Acari) in honey bee (Apis mellifera) pupae

Social insect colonies possess a range of defences which protect them against highly virulent parasites and colony collapse. The host–parasite interaction between honey bees (Apis mellifera) and the mite Varroa destructor is unusual, as honey bee colonies are relatively poorly defended against this parasite. The interaction has existed since the mid‐20th Century, when Varroa switched host to parasitize A. mellifera. The combination of a virulent parasite and relatively naïve host means that, without acaricides, honey bee colonies typically die within 3 years of Varroa infestation. A consequence of acaricide use has been a reduced selective pressure for the evolution of Varroa resistance in honey bee colonies. However, in the past 20 years, several natural‐selection‐based breeding programmes have resulted in the evolution of Varroa‐resistant populations. In these populations, the inhibition of Varroa's reproduction is a common trait. Using a high‐density genome‐wide association analysis in a Varroa‐resistant honey bee population, we identify an ecdysone‐induced gene significantly linked to resistance. Ecdysone both initiates metamorphosis in insects and reproduction in Varroa. Previously, using a less dense genetic map and a quantitative trait loci analysis, we have identified Ecdysone‐related genes at resistance loci in an independently evolved resistant population. Varroa cannot biosynthesize ecdysone but can acquire it from its diet. Using qPCR, we are able to link the expression of ecdysone‐linked resistance genes to Varroa's meals and reproduction. If Varroa co‐opts pupal compounds to initiate and time its own reproduction, mutations in the host's ecdysone pathway may represent a key selection tool for honey bee resistance and breeding.     

Aliphatic alcohols and aldehydes of the honey bee cocoon induce arrestment behavior in Varroa jacobsoni (Acari: Mesostigmata), an ectoparasite of Apis mellifera

The ectoparasitic mite Varroa jacobsoni reproduces in the capped brood of the honey bees Apis cerana and Apis mellifera. Observations on the reproductive behavior of the mite have shown a well-structured spatial allocation of its activity using the bee or cell wall for different behaviors. The resulting advantages for the parasite of this subdivision of the concealed brood environment suggests an important role for chemostimuli in these substrates. Extracts of the European honey bee cocoons induce a strong arrestment response in the mite, as indicated by prolonged periods of walking on the extracts applied on a semipermeable membrane and by systematically returning to the stimulus after encountering the treatment borders. Two thin-layer chromatography fractions of the cocoon extract eliciting arrestment were found to contain saturated C₁₇ to C₂₂ primary aliphatic alcohols and C₁₉ to C₂₂ aldehydes. We analyzed extracts of the cocoon and different larvae, pupae, and adults of both worker and drone A. mellifera to determine the relative amounts of these chemostimuli in the different substrates employed by Varroa. Both aldehydes and alcohols were more abundant in the cocoon than in the cuticle of adult or developing bees. Mixtures of the aliphatic alcohols and aldehydes at the proportions found in the cocoons acted synergistically on the arrestment response, but this activity disappeared when mixed in equal amounts. When these oxygenated chemostimuli were mixed with C₁₉ to C₂₅ alkanes at the proportions found in the cocoon extract, we observed a significantly lower threshold for the chemostimulant mixture. These results indicate how Varroa may use mixtures of rarer products to differentiate between substrates and host stages during its developmental cycle within honey bee brood cells. Arch. Insect Biochem. Physiol. 37:129–145, 1998. © 1998 Wiley-Liss, Inc.     

Deformed wing virus associated with <Emphasis Type="Italic">Tropilaelaps mercedesae</Emphasis> infesting European honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>)

Mites in the genus Tropilaelaps (Acari: Laelapidae) are ectoparasites of the brood of honey bees (Apis spp.). Different Tropilaelaps subspecies were originally described from Apis dorsata, but a host switch occurred to the Western honey bee, Apis mellifera, for which infestations can rapidly lead to colony death. Tropilaelaps is hence considered more dangerous to A. mellifera than the parasitic mite Varroa destructor. Honey bees are also infected by many different viruses, some of them associated with and vectored by V. destructor. In recent years, deformed wing virus (DWV) has become the most prevalent virus infection in honey bees associated with V. destructor. DWV is distributed world-wide, and found wherever the Varroa mite is found, although low levels of the virus can also be found in Varroa free colonies. The Varroa mite transmits viral particles when feeding on the haemolymph of pupae or adult bees. Both the Tropilaelaps mite and the Varroa mite feed on honey bee brood, but no observations of DWV in Tropilaelaps have so far been reported. In this study, quantitative real-time RT-PCR was used to show the presence of DWV in infested brood and Tropilaelaps mercedesae mites collected in China, and to demonstrate a close quantitative association between mite-infested pupae of A. mellifera and DWV infections. Phylogenetic analysis of the DWV sequences recovered from matching pupae and mites revealed considerable DWV sequence heterogeneity and polymorphism. These polymorphisms appeared to be associated with the individual brood cell, rather than with a particular host.     

Evaluation of the Distribution and Impacts of Parasites,Pathogens, and Pesticides on Honey Bee (Apis mellifera) Populations in East Africa

In East Africa, honey bees (Apis mellifera) provide critical pollination services and income for small-holder farmers and rural families. While honey bee populations in North America and Europe are in decline, little is known about the status of honey bee populations in Africa. We initiated a nationwide survey encompassing 24 locations across Kenya in 2010 to evaluate the numbers and sizes of honey bee colonies, assess the presence of parasites (Varroa mites and Nosema microsporidia) and viruses, identify and quantify pesticide contaminants in hives, and assay for levels of hygienic behavior. Varroa mites were present throughout Kenya, except in the remote north. Levels of Varroa were positively correlated with elevation, suggesting that environmental factors may play a role in honey bee host-parasite interactions. Levels of Varroa were negatively correlated with levels of hygienic behavior: however, while Varroa infestation dramatically reduces honey bee colony survival in the US and Europe, in Kenya Varroa presence alone does not appear to impact colony size. Nosema apis was found at three sites along the coast and one interior site. Only a small number of pesticides at low concentrations were found. Of the seven common US/European honey bee viruses, only three were identified but, like Varroa, were absent from northern Kenya. The number of viruses present was positively correlated with Varroa levels, but was not correlated with colony size or hygienic behavior. Our results suggest that Varroa, the three viruses, and Nosema have been relatively recently introduced into Kenya, but these factors do not yet appear to be impacting Kenyan bee populations. Thus chemical control for Varroa and Nosema are not necessary for Kenyan bees at this time. This study provides baseline data for future analyses of the possible mechanisms underlying resistance to and the long-term impacts of these factors on African bee populations.     

Host brood traits,independent of adult behaviours,reduce Varroa destructor mite reproduction in resistant honeybee populations

The ectoparasitic mite Varroa destructor is an invasive species of Western honey bees (Apis mellifera) and the largest pathogenic threat to their health world-wide. Its successful invasion and expansion is related to its ability to exploit the worker brood for reproduction, which results in an exponential population growth rate in the new host. With invasion of the mite, wild honeybee populations have been nearly eradicated from Europe and North America, and the survival of managed honeybee populations relies on mite population control treatments. However, there are a few documented honeybee populations surviving extended periods without control treatments due to adapted host traits that directly impact Varroa mite fitness. The aim of this study was to investigate if Varroa mite reproductive success was affected by traits of adult bee behaviours or by traits of the worker brood, in three mite-resistant honey bee populations from Sweden, France and Norway. The mite’s reproductive success was measured and compared in broods that were either exposed to, or excluded from, adult bee access. Mite-resistant bee populations were also compared with a local mite-susceptible population, as a control group. Our results show that mite reproductive success rates and mite fecundity in the three mite-resistant populations were significantly different from the control population, with the French and Swedish populations having significantly lower reproductive rates than the Norwegian population. When comparing mite reproduction in exposed or excluded brood treatments, no differences were observed, regardless of population. This result clearly demonstrates that Varroa mite reproductive success can be suppressed by traits of the brood, independent of adult worker bees.     

Phenotypic and Genetic Analyses of the Varroa Sensitive Hygienic Trait in Russian Honey Bee (Hymenoptera: Apidae) Colonies

Varroa destructor continues to threaten colonies of European honey bees. General hygiene, and more specific Varroa Sensitive Hygiene (VSH), provide resistance towards the Varroa mite in a number of stocks. In this study, 32 Russian (RHB) and 14 Italian honey bee colonies were assessed for the VSH trait using two different assays. Firstly, colonies were assessed using the standard VSH behavioural assay of the change in infestation of a highly infested donor comb after a one-week exposure. Secondly, the same colonies were assessed using an “actual brood removal assay” that measured the removal of brood in a section created within the donor combs as a potential alternative measure of hygiene towards Varroa-infested brood. All colonies were then analysed for the recently discovered VSH quantitative trait locus (QTL) to determine whether the genetic mechanisms were similar across different stocks. Based on the two assays, RHB colonies were consistently more hygienic toward Varroa-infested brood than Italian honey bee colonies. The actual number of brood cells removed in the defined section was negatively correlated with the Varroa infestations of the colonies (r² = 0.25). Only two (percentages of brood removed and reproductive foundress Varroa) out of nine phenotypic parameters showed significant associations with genotype distributions. However, the allele associated with each parameter was the opposite of that determined by VSH mapping. In this study, RHB colonies showed high levels of hygienic behaviour towards Varroa -infested brood. The genetic mechanisms are similar to those of the VSH stock, though the opposite allele associates in RHB, indicating a stable recombination event before the selection of the VSH stock. The measurement of brood removal is a simple, reliable alternative method of measuring hygienic behaviour towards Varroa mites, at least in RHB stock.     

Biology and control of Varroa destructor

The ectoparasitic honey bee mite Varroa destructor was originally confined to the Eastern honey bee Apis cerana. After a shift to the new host Apis mellifera during the first half of the last century, the parasite dispersed world wide and is currently considered the major threat for apiculture. The damage caused by Varroosis is thought to be a crucial driver for the periodical colony losses in Europe and the USA and regular Varroa treatments are essential in these countries. Therefore, Varroa research not only deals with a fascinating host–parasite relationship but also has a responsibility to find sustainable solutions for the beekeeping.This review provides a survey of the current knowledge in the main fields of Varroa research including the biology of the mite, damage to the host, host tolerance, tolerance breeding and Varroa treatment. We first present a general view on the functional morphology and on the biology of the Varroa mite with special emphasis on host–parasite interactions during reproduction of the female mite. The pathology section describes host damage at the individual and colony level including the problem of transmission of secondary infections by the mite. Knowledge of both the biology and the pathology of Varroa mites is essential for understanding possible tolerance mechanisms in the honey bee host. We comment on the few examples of natural tolerance in A. mellifera and evaluate recent approaches to the selection of Varroa tolerant honey bees. Finally, an extensive listing and critical evaluation of chemical and biological methods of Varroa treatments is given.This compilation of present-day knowledge on Varroa honey bee interactions emphasizes that we are still far from a solution for Varroa infestation and that, therefore, further research on mite biology, tolerance breeding, and Varroa treatment is urgently needed.     

Bidirectional Transfer of RNAi between Honey Bee and Varroa destructor: Varroa Gene Silencing Reduces Varroa Population

The mite Varroa destructor is an obligatory ectoparasite of the honey bee (Apis mellifera) and is one of the major threats to apiculture worldwide. We previously reported that honey bees fed on double-stranded RNA (dsRNA) with a sequence homologous to that of the Israeli acute paralysis virus are protected from the viral disease. Here we show that dsRNA ingested by bees is transferred to the Varroa mite and from mite on to a parasitized bee. This cross-species, reciprocal exchange of dsRNA between bee and Varroa engendered targeted gene silencing in the latter, and resulted in an over 60% decrease in the mite population. Thus, transfer of gene-silencing-triggering molecules between this invertebrate host and its ectoparasite could lead to a conceptually novel approach to Varroa control.     

Behavioural responses of Varroa destructor (Acari: Varroidae) to extracts of larvae, cocoons and brood food of worker and drone honey bees, Apis mellifera (Hymenoptera: Apidae)

Abstract. Varroa destructor is a parasitic mite of the honey bee species Apis cerana Fabr . and A. mellifera L. Mature females reproduce on the immature stages of their hosts, producing more viable female offspring on drone hosts than on worker hosts. Thus, immature drones are more likely to be infested with mites than immature workers. To investigate the hypothesis that differences in host chemistries underlie the biased distribution of mites between worker and drone brood, the arrestment responses of mites to solvent extracts of a number of stimuli normally encountered by a mite during its life cycle were measured. Mites were arrested by cuticular extracts of worker and drone larvae obtained at 0, 24 and 48 h prior to the time when cell capping is completed. Mites were also arrested by extracts of worker and drone, brood food and cocoons, and by a blend of synthetic fatty acid esters previously shown to be active in the host acquisition process. In a wind tunnel bioassay, mites were attracted to odours from living fifth-instar worker and drone larvae, but not to volatiles from cocoons, brood food or a blend of fatty acid esters. The sex of the host was not an important factor affecting the behavioural responses of the mites in any assay. We conclude that host kairomones play a role in the host acquisition process, but we found no evidence to support the hypothesis that mites use these substances to differentiate between worker and drone brood.     

A Game Theoretical Analysis of the Mating Sign Behavior in the Honey Bee

Queens of the honey bee, Apis mellifera (L.), exhibit extreme polyandry, mating with up to 45 different males (drones). This increases the genetic diversity of their colonies, and consequently their fitness. After copulation, drones leave a mating sign in the genital opening of the queen which has been shown to promote additional mating of the queen. On one hand, this signing behavior is beneficial for the drone because it increases the genetic diversity of the resulting colony that is to perpetuate his genes. On the other hand, it decreases the proportion of the drone??s personal offspring among colony members which is reducing drone fitness. We analyze the adaptiveness and evolutionary stability of this drone??s behavior with a game-theoretical model. We find that theoretically both the strategy of leaving a mating sign and the strategy of not leaving a mating sign can be evolutionary stable, depending on natural parameters. However, the signing strategy is not favored for most scenarios, including the cases that are biologically plausible in reference to empirical data. We conclude that leaving a sign is not in the interest of the drone unless it serves biological functions other than increasing subsequent queen mating chances. Nevertheless, our analysis can also explain the prevalence of such a behavior of honey bee drones by a very low evolutionary pressure for an invasion of the nonsigning strategy.     

Ecdysteroid titers in pupae of highly social bees relate to distinct modes of caste development

Modifications in endocrine programs are common mechanisms that generate alternative phenotypes. In order to understand how such changes may have evolved, we analyzed the pupal ecdysteroid titers in two closely related, highly social bees: the honey bee, Apis mellifera, and a stingless bee, Melipona quadrifasciata. In both species, the ecdysteroid titers in queens reached their peak levels earlier than in workers. Titer levels at peak maxima did not differ for the honey bee castes, but in Melipona they were twofold higher in queens than in workers. During the second half of pupal development, when the ecdysteroid titers decrease and the cuticle progressively melanizes, the titer in honey bee queens remained higher than in workers, while the reverse situation was observed in Melipona. Application of the juvenile hormone analog Pyriproxyfen^® to spinning-stage larvae of Melipona induced queen development. Endocrinologically this was manifest in a queen-like profile of the pupal ecdysteroid titer. Comparing these data with previous results on preimaginal hormone titers in another stingless bee, we conclude that the timing and height of the pupal ecdysteroid peak may depend on the nature of the specific stimuli that initially trigger diverging queen/worker development. In contrast, the interspecific differences in the late pupal ecdysteroid titer profiles mainly seem to be related to caste-specific programs in tissue differentiation, including cuticle pigmentation.     

The effects of honey bee (Apis mellifera L.) queen reproductive potential on colony growth

Reproduction in species of eusocial insects is monopolized by one or a few individuals, while the remaining colony tasks are performed by the worker caste. This reproductive division of labor is exemplified by honey bees (Apis mellifera L.), in which a single, polyandrous queen is the sole colony member that lays fertilized eggs. Previous work has revealed that the developmental fate of honey bee queens is highly plastic, with queens raised from younger worker larvae exhibiting higher measures in several aspects of reproductive potential compared to queens raised from older worker larvae. Here, we investigated the effects of queen reproductive potential (“quality”) on the growth and winter survival of newly established honey bee colonies. We did so by comparing the growth of colonies headed by “high-quality” queens (i.e., those raised from young worker larvae, which are more queen-like morphologically) to those headed by “low-quality” queens (i.e., those raised from older worker larvae, which are more worker-like morphologically). We confirmed that queens reared from young worker larvae were significantly larger in size than queens reared from old worker larvae. We also found a significant positive effect of queen grafting age on a colony’s production of worker comb, drone comb, and stored food (honey and pollen), although we did not find a statistically significant difference in the production of worker and drone brood, worker population, and colony weight. Our results provide evidence that in honey bees, queen developmental plasticity influences several important measures of colony fitness. Thus, the present study supports the idea that a honey bee colony can be viewed (at least in part) as the expanded phenotype of its queen, and thus selection acting predominantly at the colony level can be congruent with that at the individual level.     

大蜂螨对一些气味物质的趋性

狄斯瓦螨Varroa destructor Anderson & Trueman是意大利蜜蜂Apis mellifera Spinola的主要外寄生螨。雌成螨在幼虫巢房封盖前不久侵入幼虫巢房,并开始繁殖为害。从雌成螨在一个很短的时间内进入蜜蜂幼虫巢房,以及雄蜂幼虫巢房蜂螨的寄生率明显高于工蜂幼虫巢房的现象,表明蜜蜂幼虫体表一些信息素(semiochemicals)可能起着重要的引诱作用。作者对与大蜂螨相关的19种气味物质进行筛选,并对封盖前工蜂幼虫和雄蜂幼虫表皮挥发物进行气谱及气-质联谱测定。结果表明:雄蜂6龄幼虫对大蜂螨的引诱作用显著高于丁香水等10种气味物质。工蜂和雄蜂末龄幼虫体表挥发物的共有组份是9-二十三烯(C23H46),但它在雄蜂幼虫中所占的比例要明显高于工蜂幼虫。工蜂幼虫的特有主要组分是十八烷(C18H38)和9-甲基十九烷(C19H40);而雄蜂幼虫的特有主要组分是二十五烷(C25H52)和二十三烷(C23H48)。     

Survival of the mite Varroa jacobsoni Oud. (Mesostigmata: Varroidae) in broodless colonies of the honey bee Apis mellifera L. (Hymenoptera: Apidae)

Varroa mite free colonies of the honey bee Apis mellifera L. were artificially infested, with either parasitized bees or infested worker brood. Queens were kept in cages to provide broodless conditions during the experiment. Parasites that fell to the bottom of the hive were monitored at 3–4 days intervals for three months. An acaricide treatment was used to recover mites still alive after this time period. Survivorship at each interval was calculated and life table functions of the phoretic mite cohorts were obtained. Trends in survival of Varroa cohorts showed maximum lifespans ranging from 80 to 100 days. Life expectancy of these phoretic cohorts at the beginning of the experiment ranges between 19 to 41, with a mean of 31 days.     

Differential periods ofVarroa mite invasion into worker and drone cells of honey bees

Invasion ofVarroa mites into honeybee brood cells was studied in an observation hive, using combs with cell openings at one side only. The cell bottoms had been replaced by a transparent sheet, through which mites were clearly visible after invasion into a cell. Mites invaded worker cells from 15–20 h preceding cell capping, whereas they invaded drone cells from 40–50 h preceding capping. The larger number of mites generally found in drone cells, when compared to worker cells, may be partly due to the longer period of mite invasion into drone brood.     

Can We Disrupt the Sensing of Honey Bees by the Bee Parasite Varroa destructor?

BackgroundThe ectoparasitic mite, Varroa destructor, is considered to be one of the most significant threats to apiculture around the world. Chemical cues are known to play a significant role in the host-finding behavior of Varroa. The mites distinguish between bees from different task groups, and prefer nurses over foragers. We examined the possibility of disrupting the Varroa – honey bee interaction by targeting the mite''s olfactory system. In particular, we examined the effect of volatile compounds, ethers of cis 5-(2′-hydroxyethyl) cyclopent-2-en-1-ol or of dihydroquinone, resorcinol or catechol. We tested the effect of these compounds on the Varroa chemosensory organ by electrophysiology and on behavior in a choice bioassay. The electrophysiological studies were conducted on the isolated foreleg. In the behavioral bioassay, the mite''s preference between a nurse and a forager bee was evaluated.ConclusionsThese data indicate the potential of the selected compounds to disrupt the Varroa - honey bee associations, thus opening new avenues for Varroa control.     

Quantifying honey bee mating range and isolation in semi-isolated valleys by DNA microsatellite paternity analysis

Honey bee males and queens mate in mid air and can fly many kilometres on their nuptial flights. The conservation of native honey bees, such as the European black bee (Apis mellifera mellifera), therefore, requires large isolated areas to prevent hybridisation with other subspecies, such as A. m. ligustica or A. m. carnica, which may have been introduced by beekeepers. This study used DNA microsatellite markers to determine the mating range of A. m. mellifera in two adjacent semi-isolated valleys (Edale and Hope Valley) in the Peak District National Park, England, in order to assess their suitability for native honey bee conservation and as isolated mating locations. Three apiaries were set up in each valley, each containing 12 colonies headed by a virgin queen and 2 queenright drone producing hives. The virgin queens were allowed to mate naturally with drones from the hives we had set up and with drones from hives owned by local beekeepers. After mating, samples of worker larvae were taken from the 41 queens that mated successfully and genotyped at 11 DNA microsatellite loci. Paternity analyses were then carried out to determine mating distances and isolation. An average of 10.2 fathers were detected among the 16 worker progeny. After correction for non-detection and non-sampling errors, the mean effective mating frequency of the test queens was estimated to be 17.2, which is a normal figure for honey bees. Ninety percent of the matings occurred within a distance of 7.5 km, and fifty percent within 2.5 km. The maximal mating distance recorded was 15 km. Queens and drones did occasionally mate across the borders between the two valleys, showing that the dividing mountain ridge Losehill does not provide complete isolation. Nevertheless, in the most isolated part of Edale sixty percent of all matings were to drones from Edale hives. The large majority of observed mating distances fell within the range of Hope Valley, making this site a suitable location for the long term conservation of a breeding population of black bees.