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.     

Recipe for a Busy Bee: MicroRNAs in Honey Bee Caste Determination

Social caste determination in the honey bee is assumed to be determined by the dietary status of the young larvae and translated into physiological and epigenetic changes through nutrient-sensing pathways. We have employed Illumina/Solexa sequencing to examine the small RNA content in the bee larval food, and show that worker jelly is enriched in miRNA complexity and abundance relative to royal jelly. The miRNA levels in worker jelly were 7–215 fold higher than in royal jelly, and both jellies showed dynamic changes in miRNA content during the 4^th to 6^th day of larval development. Adding specific miRNAs to royal jelly elicited significant changes in queen larval mRNA expression and morphological characters of the emerging adult queen bee. We propose that miRNAs in the nurse bee secretions constitute an additional element in the regulatory control of caste determination in the honey bee.     

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.     

中华蜜蜂雄蜂脑部组织结构观察

通过组织化学方法,对中华蜜蜂Apis cerana cerana Fabricius雄蜂的脑部的形态结构进行观察。结果表明,雄蜂的脑由前脑、中脑和后脑三部分构成,前脑视叶两侧具有大而显著的复眼,而其他结构相对较小。蕈形体在脑中所占的比例小于工蜂和蜂王;中心体的比例小于工蜂,与蜂王接近;中脑的嗅叶相对较为发达,这使它们在同蜂王的交配过程中,能够更灵敏地接收来自于蜂王性外激素的刺激。中华蜜蜂雄蜂的嗅叶具有性二态现象,但是与意大利蜜蜂Apis mellifera L.雄蜂发达的巨大纤维球复合体相比,中华蜜蜂并不明显;除此之外,它们在脑部结构上没有显著差异。     

Effects of insemination quantity on honey bee queen physiology

Mating has profound effects on the physiology and behavior of female insects, and in honey bee (Apis mellifera) queens, these changes are permanent. Queens mate with multiple males during a brief period in their early adult lives, and shortly thereafter they initiate egg-laying. Furthermore, the pheromone profiles of mated queens differ from those of virgins, and these pheromones regulate many different aspects of worker behavior and colony organization. While it is clear that mating causes dramatic changes in queens, it is unclear if mating number has more subtle effects on queen physiology or queen-worker interactions; indeed, the effect of multiple matings on female insect physiology has not been broadly addressed. Because it is not possible to control the natural mating behavior of queens, we used instrumental insemination and compared queens inseminated with semen from either a single drone (single-drone inseminated, or SDI) or 10 drones (multi-drone inseminated, or MDI). We used observation hives to monitor attraction of workers to SDI or MDI queens in colonies, and cage studies to monitor the attraction of workers to virgin, SDI, and MDI queen mandibular gland extracts (the main source of queen pheromone). The chemical profiles of the mandibular glands of virgin, SDI, and MDI queens were characterized using GC-MS. Finally, we measured brain expression levels in SDI and MDI queens of a gene associated with phototaxis in worker honey bees (Amfor). Here, we demonstrate for the first time that insemination quantity significantly affects mandibular gland chemical profiles, queen-worker interactions, and brain gene expression. Further research will be necessary to elucidate the mechanistic bases for these effects: insemination volume, sperm and seminal protein quantity, and genetic diversity of the sperm may all be important factors contributing to this profound change in honey bee queen physiology, queen behavior, and social interactions in the colony.     

Sex-specific developmental profiles of juvenile hormone synthesis in honey bee larvae

Summary Juvenile hormone synthesis in drone larvae of the honey bee was measured by an in vitro radiochemical assay. The developmental profile of corpora allata activity in male larvae showed considerable differences from queen larvae, the presumptive reproductive females, and was comparable to workers, the sterile female morph. Drone and worker larvae, however, differed drastically in the regulation of juvenile hormone biosynthesis, as revealed by the addition of farnesoic acid to the culture medium. This precursor stimulated juvenile hormone synthesis of drone glands nearly eightfold, whereas in worker larvae it is known to lead to an accumulation of methyl farnesoate. The sex-specific differences in endocrine activity indicate a role for juvenile hormone in the expression of genetically determined sexually dimorphic characters during metamorphosis, a role not currently accounted for in models describing endocrine regulation of insect development. Correspondence to: K. Hartfelder     

Organization of the antennal lobe in the queen honey bee,Apis mellifera L. (Hymenoptera : Apidae)

Antennal afferent pathway topography was studied in the queen honey bee, Apis mellifera L. (Hymenoptera : Apidae) by staining with cobalt chloride applied directly to the cut antennal axons. Antennal lobe organization in the queen was compared with those in worker and drone bees. The organization is similar in queen and worker bees. For the first time in a female insect the possible existence of a macroglomerulus is shown, which may be involved in the processing of species-specific information. A comparative quantitative neuromorphological study of the glomeruli was performed between young queens (8-day old) and 1-yr-old queens. The mean volume of the glomeruli is 46% greater in the older queens.     

Regulation of oogenesis in honey bee workers via programed cell death

Reproductive division of labour characterises eusociality. Currently little is known about the mechanisms that underlie the ‘sterility’ of the worker caste, but queen pheromone plays a major role in regulating the reproductive state. Here we investigate oogenesis in the young adult honey bee worker ovary in the presence of queen pheromone and in its absence. When queen pheromone is absent, workers can activate their ovaries and have well-developed follicles. When queen pheromone is present, even though workers have non-activated ovaries, they continually produce oocytes which are aborted at an early stage. Therefore, irrespective of the presence of the queen, the young adult worker ovary contains oocytes. By this means young workers retain reproductive plasticity. The degeneration of the germ cells in the ovarioles of workers in the presence of queen pheromone has the morphological hallmarks of programmed cell death. Therefore the mechanistic basis of ‘worker sterility’ relies in part on the regulation of oogenesis via programmed cell death. Our results suggest that honey bees have co-opted a highly conserved checkpoint at mid-oogenesis to regulate the fertility of the worker caste.     

王浆主蛋白MRJP7基因在意大利蜜蜂体内的表达

王浆蛋白是蜂王浆生物功能的物质基础,是由王浆蛋白基因家族(mrjps)编码合成的。但部分家族成员如MRJP7在王浆中的含量极少甚至检测不到。基因功能与其在生物体内的时空表达特性相关,为探究mrjp7的生物学功能,本研究利用荧光定量PCR技术对mrjp7在不同发育时期的工蜂和成年工蜂、雄蜂和蜂王的不同组织部位的表达进行定量检测。结果显示mrjp7在成年雄蜂体内的表达水平最低,成年蜂王次之,且在它们的各不同组织部位之间的表达量差异较小。该基因在工蜂幼虫和蛹期的表达同样较低,但在羽化后9日龄前后的哺育蜂王浆腺和头部特异性高表达,这与哺育蜂分泌蜂王浆哺育幼虫和蜂王的功能是相适应的,该结果在转录水平上证实了mrjp7的营养功能,为进一步的研究和应用打下了理论基础。     

Behavior and molecular physiology of nurses of worker and queen larvae in honey bees (Apis mellifera)

In a honey bee colony, worker bees rear a new queen by providing her with a larger cell in which to develop and a large amount of richer food (royal jelly). Royal jelly and worker jelly (fed to developing worker larvae) differ in terms of sugar, vitamin, protein and nucleotide composition. Here we examined whether workers attending queen and worker larvae are separate specialized sub-castes of the nurse bees. We collected nurse bees attending queen larvae (AQL) and worker larvae (AWL) and compared gene expression profiles of hypopharyngeal gland tissues, using Solexa/Illumina digital gene expression tag profiling (DGE). Significant differences in gene expression were found that included a disproportionate number of genes involved in glandular secretion and royal jelly synthesis. However behavioral observations showed that these were not two entirely distinct populations. Nurse workers were observed attending both worker larvae and queen larvae, and there was no evidence of a specialized group of workers that preferentially or exclusively attended developing queens. Nevertheless, AQL attended larvae more frequently compared to AWL, suggesting that nurses sampled attending queen larvae may have been the most active nurses. This study serves as another example of the relationship between differences in gene expression and behavioral specialisation in honey bees.     

What's in that package? An evaluation of quality of package honey bee (Hymenoptera: Apidae) shipments in the United States

To replace deceased colonies or to increase the colony numbers, beekeepers often purchase honey bees, Apis mellifera L., in a package, which is composed of 909-1,364 g (2-3 lb) of worker bees and a mated queen. Packages are typically produced in warm regions of the United States in spring and shipped throughout the United States to replace colonies that perished during winter. Although the package bee industry is effective in replacing colonies lost in winter, packages also can be an effective means of dispersing diseases, parasites, and undesirable stock to beekeepers throughout the United States. To evaluate the quality of packages, we examined 48 packages representing six lines of bees purchased in the spring 2006. We estimated levels of the parasitic mite Varroa destructor Anderson & Trueman and the percentage of drone (male) honey bees received in packages. We surveyed for presence of the tracheal honey bee mite, Acarapis woodi (Rennie), and a microsporidian parasite, Nosema spp., in the shipped bees. We found significant differences in both the mean Varroa mite per bee ratios (0.004-0.054) and the average percentage of drones (0.04-5.1%) in packages from different producers. We found significant differences in the number of Nosema-infected packages (0.0-75.0%) among the six lines. No packages contained detectable levels ofA. woodi. Considering the observed variability among honey bee packages, beekeepers should be aware of the potential for pest and disease infestations and high drone levels in packages.     

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)。     

Representational Difference Analysis (RDA) reveals differential expression of conserved as well as novel genes during caste-specific development of the honey bee (Apis mellifera L.) ovary

In highly eusocial insects, such as the honey bee, Apis mellifera, the reproductive bias has become embedded in morphological caste differences. These are most expressively denoted in ovary size, with adult queens having large ovaries consisting of 150-200 ovarioles each, while workers typically have only 1-20 ovarioles per ovary. This morphological differentiation is a result of hormonal signals triggered by the diet change in the third larval instar, which eventually generate caste-specific gene expression patterns. To reveal these we produced differential gene expression libraries by Representational Difference Analysis (RDA) for queen and worker ovaries in a developmental stage when cell death is a prominent feature in the ovarioles of workers, whereas all ovarioles are maintained and extend in length in queens. In the queen library, 48% of the gene set represented homologs of known Drosophila genes, whereas in the worker ovary, the largest set (59%) were ESTs evidencing novel genes, not even computationally predicted in the honey bee genome. Differential expression was confirmed by quantitative RT-PCR for a selected gene set, denoting major differences for two queen and two worker library genes. These included two unpredicted genes located in chromosome 11 (Group11.35 and Group11.31, respectively) possibly representing long non-coding RNAs. Being candidates as modulators of ovary development, their expression and functional analysis should be a focal point for future studies.     

短舌熊蜂及红光熊蜂耐寒力的测定

以过冷却点和冰点为评价指标,对短舌熊蜂Bombus terrestris的幼虫,蛹,成年工蜂,成年雄蜂,处女蜂王,越冬后的蜂王及红光熊蜂Bombus ignitus的成年工蜂,成年雄蜂,处女蜂王的耐寒力进行检测。结果显示,短舌熊蜂幼虫期耐寒力最低,其次是蛹,工蜂和雄蜂,处女王较高。耐寒力最高的是越冬后的蜂王,其含水量也最低。将短舌熊蜂与红光熊蜂的成年工蜂,成年雄蜂和处女蜂王三型蜂分别进行对比,结果显示,红光熊蜂成年雄蜂与处女蜂王的耐寒力要比短舌熊蜂高。样本的湿重和含水量与过冷却点和冰点无显著相关性。     

Larval juvenile hormone treatment affects pre-adult development,but not adult age at onset of foraging in worker honey bees (Apis mellifera)

Previous research has shown that juvenile hormone (JH) titers increase as adult worker honey bees age and treatments with JH, JH analogs and JH mimics induce precocious foraging. Larvae from genotypes exhibiting faster adult behavioral development had significantly higher levels of juvenile hormone during the 2nd and 3rd larval instar. It is known that highly increased JH during this period causes the totipotent female larvae to differentiate into a queen. We treated third instar larvae with JH to test the hypothesis that this time period may be a developmental critical period for organizational effects of JH on brain and behavior also in the worker caste, such that JH treatment at a lower level than required to produce queens will speed adult behavioral development in workers. Larval JH treatment did not influence adult worker behavioral development. However, it made pre-adult development more queen-like in two ways: treated larvae were capped sooner by adult bees, and emerged from pupation earlier. These results suggest that some aspects of honey bee behavioral development may be relatively insensitive to pre-adult perturbation. These results also suggest JH titer may be connected to cues perceived by the adult bees indicating larval readiness for pupation resulting in adult bee cell capping behavior.     

Reduction of tracheal mite parasitism of honey bees by swarming.

Based on population dynamics, tracheal mite (Acarapis woodi) parasitism of colonies of honey bees (Apis mellifera) appears to be, potentially at least, regulatory and stable. Empirical and theoretical considerations suggest, however, that intracolony population dynamics of mite-honey bee worker seem to be unstable in managed situations where honey bee worker population is allowed to grow unchecked. Experimental studies showed that tracheal mite population levels increased in a managed honey bee colony but were impaired in one in which brood rearing was interrupted by loss of the queen. Mite densities but not prevalence were lowered in experimental swarms kept from rearing brood. We propose that swarming reduces mite density within a colony, therefore implicating modern techniques of hive management in the sudden historical appearance of the mite on the Isle of Wight.     

Three QTL in the honey bee Apis mellifera L. suppress reproduction of the parasitic mite Varroa destructor

Varroa destructor is a highly virulent ectoparasitic mite of the honey bee Apis mellifera and a major cause of colony losses for global apiculture. Typically, chemical treatment is essential to control the parasite population in the honey bee colony. Nevertheless a few honey bee populations survive mite infestation without any treatment. We used one such Varroa mite tolerant honey bee lineage from the island of Gotland, Sweden, to identify quantitative trait loci (QTL) controlling reduced mite reproduction. We crossed a queen from this tolerant population with drones from susceptible colonies to rear hybrid queens. Two hybrid queens were used to produce a mapping population of haploid drones. We discriminated drone pupae with and without mite reproduction, and screened the genome for potential QTL using a total of 216 heterozygous microsatellite markers in a bulk segregant analysis. Subsequently, we fine mapped three candidate target regions on chromosomes 4, 7, and 9. Although the individual effect of these three QTL was found to be relatively small, the set of all three had significant impact on suppression of V. destructor reproduction by epistasis. Although it is in principle possible to use these loci for marker-assisted selection, the strong epistatic effects between the three loci complicate selective breeding programs with the Gotland Varroa tolerant honey bee stock.     

Juvenile hormone pathway in honey bee larvae: A source of possible signal molecules for the reproductive behavior of Varroa destructor

The parasitic mite Varroa destructor devastates honey bee (Apis mellifera) colonies around the world. Entering a brood cell shortly before capping, the Varroa mother feeds on the honey bee larvae. The hormones 20‐hydroxyecdysone (20E) and juvenile hormone (JH), acquired from the host, have been considered to play a key role in initiating Varroa''s reproductive cycle. This study focuses on differential expression of the genes involved in the biosynthesis of JH and ecdysone at six time points during the first 30 hr after cell capping in both drone and worker larvae of A. mellifera. This time frame, covering the conclusion of the honey bee brood cell invasion and the start of Varroa''s ovogenesis, is critical to the successful initiation of a reproductive cycle. Our findings support a later activation of the ecdysteroid cascade in honey bee drones compared to worker larvae, which could account for the increased egg production of Varroa in A. mellifera drone cells. The JH pathway was generally downregulated confirming its activity is antagonistic to the ecdysteroid pathway during the larva development. Nevertheless, the genes involved in JH synthesis revealed an increased expression in drones. The upregulation of jhamt gene involved in methyl farnesoate (MF) synthesis came into attention since the MF is not only a precursor of JH but it is also an insect pheromone in its own right as well as JH‐like hormone in Acari. This could indicate a possible kairomone effect of MF for attracting the mites into the drone brood cells, along with its potential involvement in ovogenesis after the cell capping, stimulating Varroa''s initiation of egg laying.