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Bacterial diversity in worker adults of Apis mellifera capensis and Apis mellifera scutellata (Insecta: Hymenoptera) assessed using 16S rRNA sequences.

High-fidelity PCR of 16S rRNA sequences was used to identify bacteria associated with worker adults of the honeybee subspecies Apis mellifera capensis and Apis mellifera scutellata. An expected approximately 1.5-kb DNA band, representing almost the entire length of the 16S rRNA gene, was amplified from both subspecies and cloned. Ten unique sequences were obtained: one sequence each clustered with Bifidobacterium (Gram-positive eubacteria), Lactobacillus (Gram-positive eubacteria), and Gluconacetobacter (Gram-negative alpha-proteobacteria); two sequences each clustered with Simonsiella (beta-proteobacteria) and Serratia (gamma-proteobacteria); and three sequences each clustered with Bartonella (alpha-proteobacteria). Although the sequences relating to these six bacterial genera initially were obtained from either A. m. capensis or A. m. scutellata or both, newly designed honeybee-specific 16S rRNA primers subsequently amplified all sequences from all individual workers of both subspecies. Attempts to amplify these sequences from eggs have failed. However, the wsp primers designed to amplify Wolbachia DNA from arthropods, including these bees, consistently produced a 0.6-kb DNA band from individual eggs, indicating that amplifiable bacterial DNA was present. Hence, the 10 bacteria could have been acquired orally from workers or from other substrates. This screening of 16S rRNA sequences from A. m. capensis and A. m. scutellata found sequences related to Lactobacillus and Bifidobacterium which previously had been identified from other honeybee subspecies, as well as sequences related to Bartonella, Gluconacetobacter, Simonsiella/Neisseria, and Serratia, which have not been identified previously from honeybees.

Animals↗

Open-air-nesting honey bees Apis dorsata and Apis laboriosa differ from the cavity-nesting Apis mellifera and Apis cerana in brood hygiene behaviour.

The cavity-nesting Apis mellifera and Apis cerana bees detect, uncap, and remove diseased brood. The hygiene behaviour of open-air-nesting bees Apis dorsata and Apis laboriosa was investigated in India and Nepal. Sealed A. dorsata pupae were pin-killed or deep-frozen. The workers removed 73 or 37% of damaged pin-killed pupae depending on the diameter of the pins, and only 7% of the frozen undamaged pupae. Migrating A. dorsata and A. laboriosa left unopened the sealed brood in deserted combs. Thus, A. dorsata and A. laboriosa do not open undamaged cells with dead brood. This behaviour is a more efficient mechanism in preventing the spread of diseases and parasitic mites than uncapping and removing dead pupae by A. mellifera and A. cerana. It may be beneficial for migrating A. dorsata and A. laboriosa to temporarily disuse part of the comb cells in exchange for arresting the mites there and thus reducing the increase of their population.

Animals↗

A comparison of the dance language in Apis mellifera carnica and Apis florea reveals striking similarities.

Honeybees have a dance language by which successful foragers inform nestmates about attractive food patches. The classical concept of dialects in the dance language of honeybees points to two differences in the dances by different species and races, firstly in the flight distance at which the dancers start performing waggle dances instead of round dances, and secondly in the circuit duration of the waggle dance performed for a given flight distance. However, recent findings have indicated that the dance language is influenced and affected by a number of parameters, both genetic and environmental. The current study was carried out to see whether the distance at which dancers change from round dances to waggle dances is statistically different in two different species, Apis mellifera carnica and A. florea and to develop a set of definitions for such comparative studies. Results show that the two species do not differ in the relative proportion of waggle dances and round dances performed at a given distance. Thus, this study points to the need of addressing the dialect question again.

Animal Communication↗

Varying degrees of Apis mellifera ligustica introgression in protected populations of the black honeybee, Apis mellifera mellifera, in northwest Europe.

The natural distribution of honeybee subspecies in Europe has been significantly affected by human activities during the last century. Non-native subspecies of honeybees have been introduced and propagated, so that native black honeybee (Apis mellifera mellifera) populations lost their identity by gene-flow or went extinct. After previous studies investigated the remaining gene-pools of native honeybees in France and Spain, we here assess the genetic composition of eight northwest European populations of the black honeybee, using both mitochondrial (restriction fragment length polymorphisms of the intergenic transfer RNAleu-COII region) and nuclear (11 microsatellite loci) markers. Both data sets show that A. m. mellifera populations still exist in Norway, Sweden, Denmark, England, Scotland and Ireland, but that they are threatened by gene flow from commercial honeybees. Both Bayesian admixture analysis of the microsatellite data and DraI-RFLP (restriction fragment length polymorphism) analysis of the intergenic region indicated that gene-flow had hardly occurred in some populations, whereas almost 10% introgression was observed in other populations. The most introgressed population was found on the Danish Island of Laeso, which is the last remaining native Danish population of A. m. mellifera and the only one of the eight investigated populations that is protected by law. We discuss how individual admixture analysis can be used to monitor the restoration of honeybee populations that suffer from unwanted hybridization with non-native subspecies.

Animals↗

Simultaneous conditioning in honeybees (Apis mellifera).

Honeybees (Apis mellifera) were classically conditioned with odor as conditioned stimulus (CS), sucrose as unconditioned stimulus (US), and proboscis extension as response. The purpose of Experiment 1 (Ns = 26 and 27) was to look for facilitation of forward conditioning by CS-US overlap, but rapid conditioning without overlap left little room for improvement. In 2 further experiments, CS and US were simultaneous, and response to odor alone was measured in subsequent tests. In Experiment 2, a Simultaneous group (N = 25) responded more to the training odor than did an Unpaired control group (N = 25). In Experiment 3, a differentially conditioned Simultaneous group (N = 29) responded more to an odor paired with sucrose in training (S+) than to an odor presented alone (S-). The implications of the results for the problem of the role of amount of reward in honeybee learning are considered.

Animals↗

Isolation and characterization of abaecin, a major antibacterial response peptide in the honeybee (Apis mellifera).

Honeybee (Apis mellifera) are frequently exposed to and likely to be infected by plant-associated bacteria. We mimicked this process by injecting bees with live bacteria and isolated five induced antibacterial substances by comparative liquid chromatographic mapping of the hemolymph. Three of these antibiotics belong to a unique family of small (18 amino acids) peptides: the apidaecins [Casteels et al. (1989) EMBO J. 8, 2387-2391]. We have now characterized a fourth bee immune response peptide. The complete sequence was established by Edman degradation of the peptide and fragments thereof. It is 34 amino acids long and contains 10 proline residues. The amino-terminal half is related to the apidaecins; similar proline motifs are also present in the amino-terminal quarter of the much longer fly diptericins. The newly identified peptide's broad spectrum, lower specific activities against Gram-negative plant pathogens and its inability to inhibit bacterial growth at medium ionic strength are different from the apidaecins. Moreover, the highest observed specific activity was against an apidaecin-resistant Xanthomonas strain. In contrast to the immediate action of apidaecins, bactericidal activity is delayed. We propose the name 'abaecin' for this new antibacterial response peptide.

Amino Acid Sequence↗

Behavioral development and olfactory learning in the honeybee (Apis mellifera).

Honeybees (Apis mellifera) can be readily conditioned in the laboratory to specific odors paired with a subsequent sucrose reward. A series of experiments are reported which demonstrate that the ability of bees to acquire and retain this learning is affected by the stage of behavioral development (caste). Results show rapid acquisition of the proboscis extension reflex (PER) conditioning in adult forager bees, however much slower acquisition and poorer retention of the same learning paradigm in younger adults, i.e., nurse bees and guard bees. Further, if nurse bees are made to forage precocially by manipulation of the hive population, these bees show excellent acquisition and retention of PER conditioning comparable to normal adult forager bees. Results are discussed in terms of olfactory learning requirements of bees performing caste-specific behaviors and the maturation of the bee nervous system.

Age Factors↗

The flight physiology of reproductives of Africanized, European, and hybrid honeybees (Apis mellifera).

Neotropical African honeybees (Apis mellifera scutellata), in the process of spreading throughout tropical and subtropical regions of the Americas, hybridize with and mostly replace European honeybees (primarily Apis mellifera mellifera and Apis mellifera ligustica). To help understand this process, we studied the effect of lineage (African, European, or hybrid) on the flight physiology of honeybee reproductives. Flight metabolic rates were higher in queens and drones of African lineage than in European or hybrid bees, as has been previously found for foraging workers. These differences were associated with higher thorax/body mass ratios and higher thorax-specific metabolic rates in African lineage bees. Queens were reared in common colonies, so these metabolic and morphological differences are likely to be genetic in origin. African drones had higher wing beat frequencies and thorax temperatures than European or hybrid bees. Hybrids were intermediate for many parameters, but hybrid queen mass-specific flight metabolic rates were low relative to Africans and were nonlinearly affected by the proportion of African lineage, consistent with some negative heterosis for this trait.

Analysis of Variance↗

Feeding the disease: The impact of nutritional supplementation on Nosema (Vairimorpha) infection in honey bees (Apis mellifera).

Honey bees (Apis mellifera) experience variable colony losses across regions and years, with infectious diseases representing a key component of colony health challenges. Among the most prevalent pathogens are the microsporidian parasites Nosema apis and Nosema ceranae, whose impacts on host survival and transmission vary widely depending on context. While nutritional supplementation is commonly used to support honey bee health, its effects on Nosema infection outcomes remain unclear. Here, we experimentally tested whether dietary enrichment alters survival and infection intensity following exposure to a mixed Nosema inoculum. Newly emerged worker bees were challenged with Nosema spores and maintained on either a basic sucrose diet or the same diet supplemented with a commercial pollen substitute. Dietary enrichment significantly increased both mortality risk and infection intensity in Nosema-infected bees, while having no detectable effect on survival in uninfected controls. These results indicate that supplementation can, counter intuitively, exacerbate nosemosis by promoting parasite replication rather than enhancing host resistance. Our findings highlight the importance of distinguishing nutritional effects on host tolerance versus resistance, and caution that interventions intended to improve bee nutrition may inadvertently increase pathogen production and transmission potential under certain conditions.

Animals↗

Acetylcholine, GABA and glutamate induce ionic currents in cultured antennal lobe neurons of the honeybee, Apis mellifera.

The honeybee, Apis mellifera, is a valuable model system for the study of olfactory coding and its learning and memory capabilities. In order to understand the synaptic organisation of olfactory information processing, the transmitter receptors of the antennal lobe need to be characterized. Using whole-cell patch-clamp recordings, we analysed the ligand-gated ionic currents of antennal lobe neurons in primary cell culture. Pressure applications of acetylcholine (ACh), gamma-amino butyric acid (GABA) or glutamate induced rapidly activating ionic currents. The ACh-induced current flows through a cation-selective ionotropic receptor with a nicotinic profile. The ACh-induced current is partially blocked by alpha-bungarotoxin. Epibatidine and imidacloprid are partial agonists. Our data indicate the existence of an ionotropic GABA receptor which is permeable to chloride ions and sensitive to picrotoxin (PTX) and the insecticide fipronil. We also identified the existence of a chloride current activated by pressure applications of glutamate. The glutamate-induced current is sensitive to PTX. Thus, within the honeybee antennal lobe, an excitatory cholinergic transmitter system and two inhibitory networks that use GABA or glutamate as their neurotransmitter were identified.

Acetylcholine↗

Thermoregulation of water collecting honey bees (Apis mellifera).

Honey bees (Apis mellifera carnica, Apidae, Hymenoptera) visited a pond in order to collect water. During their stays at the pond the body surface temperature of water foragers was measured using contactless thermography. Irrespective of the ambient temperature (T(A)) which ranged from 13.6 to 27.2 degrees C, the water carriers reached thoracic temperatures of 36-38.8 degrees C (mean values of the measuring periods). The maximum thoracic value of an individual bee was 44.5 degrees C. At higher T(A) (20.9-27.2 degrees C) head and abdomen were only about 3 degrees C and 2 degrees C on the average higher than the surroundings, respectively. In the lower range of T(A) (13.6-16.6 degrees C), however, the bees warmed their heads up to 29.2 degrees C (13 degrees C above T(A)) and the abdomen up to 23.3 degrees C (7.1 degrees C above T(A); mean values of the measuring periods).The head and abdomen were even provided independently of one another with heat from the thorax. At a higher T(A) only little heat came from the heated thorax into the abdomen, at a cooler T(A) (13.6-16.6 degrees C) more heat reached the abdomen. In all probability, at a higher T(A) only a small amount of haemolymph was pumped from the thorax into the abdomen; the most warm blood probably circulated in the head-thorax area. The average duration of stays at the pond decreased linearly from 110 to 42 s with rising T(A). Head and thorax showed great fluctuations of temperature. For example, the head was heated by 4.6 degrees C within 25 s, the thorax by 6.1 degrees C within 30 s.Foragers drinking sucrose solution are known to increase their thoracic temperature with rising concentration of the sucrose solution. The water foragers had thoracic temperatures similar to that of bees feeding on 0.5 molar sucrose solution. It is hypothesized that the foraging motivation of both groups was similar and therefore they regulated their thoraces at the same temperature level.

Journal Article↗

Male fitness of honeybee colonies (Apis mellifera L.).

Honeybees (Apis mellifera L.) have an extreme polyandrous mating system. Worker offspring of 19 naturally mated queens was genotyped with DNA microsatellites, to estimate male reproductive success of 16 drone producing colonies. This allowed for estimating the male mating success on both the colony level and the level of individual drones. The experiment was conducted in a closed population on an isolated island to exclude interferences of drones from unknown colonies. Although all colonies had produced similar numbers of drones, differences among the colonies in male mating success exceeded one order of magnitude. These differences were enhanced by the siring success of individual drones within the offspring of mated queens. The siring success of individual drones was correlated with the mating frequency at the colony level. Thus more successful colonies not only produced drones with a higher chance of mating, but also with a significantly higher proportion of offspring sired than drones from less successful colonies. Although the life cycle of honeybee colonies is very female centred, the male reproductive success appears to be a major driver of natural selection in honeybees.

Animals↗

The expression of genes encoding visual components is regulated by a circadian clock, light environment and age in the honeybee (Apis mellifera).

The honeybee, Apis mellifera, has been used as a model to study the development of the visual system and adult bee behaviour. However, the regulation of the levels of visual component genes has never been addressed in this organism. We isolated honeybee cDNAs encoding green-sensitive opsin and visual arrestin and then measured their mRNA levels in honeybee workers. Both mRNAs fluctuate on a daily cycle that depends on a pacemaker that functions separately from the pacemaker which controls rhythmic locomotor activity. The cycling-patterns of opsin and arrestin mRNAs are different from each other and are modified by light. Furthermore, light exposure can increase the absolute levels of both mRNAs and the arrestin mRNA level is also dependent on age. Consistent with these results, both mRNA levels are higher in foragers than in in-hive bees under natural conditions. This study thus shows that the expression of genes encoding visual components is regulated by multiple factors and is adjusted to the honeybees' need for vision during the day, and throughout their lives. Comparison of data obtained with honeybees and other organisms indicates that there is a link between the regulation of phototransduction components and vision-related animal behaviour.

Aging↗

The P-3 and EST loci in the honeybee Apis mellifera.

Data for Apis mellifera indicate that the P-3 proteins and one esterase enzyme are controlled by two genes, P-3 and Est, with two alleles each. The frequency of the P-3 alleles is different in the two subspecies (adansonii and ligustica), that for P-3(F) in Italian bees being 46.9% and in African 0.5%. The frequency of Est(F) is 2.8% in both populations. The Est locus has two codominant alleles and the locus P-3 has two incompletely dominant alleles; the heterozygote P-3( S)/P-3(F) shows only an intermediate band. The two loci are not genetically linked.

Alleles↗

Heterogeneity in regional GC content and differential usage of codons and amino acids in GC-poor and GC-rich regions of the genome of Apis mellifera.

The honeybee (Apis mellifera) has a genome with a wide variation in GC content showing 2 clear modal GC values, in some ways reminiscent of an isochore-like structure. To gain insight into causes and consequences of this pattern, we used a comparative approach to study the genome-wide alignment of primarily coding sequence of A. mellifera with Drosophila melanogaster and Anopheles gambiae. The latter 2 species show a higher average GC content than A. mellifera and no indications of bimodality, suggesting that the GC-poor mode is a derived condition in honeybee. In A. mellifera, synonymous sites of genes generally adopt the GC content of the region in which they reside. A large proportion of genes in GC-poor regions have not been assigned to the honeybee assembly because of the low sequence complexity of their genome neighborhood. The synonymous substitution rate between A. mellifera and the other species is very close to saturation, but analyses of nonsynonymous substitutions as well as amino acid substitutions indicate that the GC-poor regions are not evolving faster than the GC-rich regions. We describe the codon usage and amino acid usage and show that they are remarkably heterogeneous within the honeybee genome between the 2 different GC regions. Specifically, the genes located in GC-poor regions show a much larger deviation in both codon usage bias and amino acid usage from the Dipterans than the genes located in the GC-rich regions.

Amino Acids↗

Sperm storage and antioxidative enzyme expression in the honey bee, Apis mellifera.

Honey bee (Apis mellifera) sperm remains viable in the spermatheca of mated female honey bees for several years. During this time, the sperm retains respiratory activity, placing it at risk of the damaging effects of reactive oxygen species common to many biological processes. Antioxidative enzymes might help reduce this damage. Here we use quantitative real-time RT-PCR to establish gene-expression profiles in male and female honey bee reproductive tissues for three antioxidative enzymes: catalase, glutathione-S-transferase (GST) and superoxide dismutase (SOD1, cytosolic). Catalase and GST showed ten- to twenty-fold transcript increases in the sperm storage organs of mated queens vs. unmated queens, whereas SOD1 levels are high in both mated and unmated queens. Male reproductive and somatic tissues showed relatively high levels of all three antioxidant-encoding transcripts. All three enzymes screened were higher in mature males vs. young males, although this effect did not appear to be confined to reproductive tissues and, hence, need not reflect a role in sperm longevity. Furthermore, antioxidative enzyme transcripts remained present, and apparently increased, in male tissues long after sperm had matured and seminal fluid was produced. We also found measurable levels of catalase transcripts in honey bee semen. The presence of catalase transcripts in both reproductive tissues and semen in bees suggests that this enzyme might play a key role in antioxidative protection.

Age Factors↗

Thrice out of Africa: ancient and recent expansions of the honey bee, Apis mellifera.

We characterized Apis mellifera in both native and introduced ranges using 1136 single-nucleotide polymorphisms genotyped in 341 individuals. Our results indicate that A. mellifera originated in Africa and expanded into Eurasia at least twice, resulting in populations in eastern and western Europe that are geographically close but genetically distant. A third expansion in the New World has involved the near-replacement of previously introduced "European" honey bees by descendants of more recently introduced A. m. scutellata ("African" or "killer" bees). Our analyses of spatial transects and temporal series in the New World revealed differential replacement of alleles derived from eastern versus western Europe, with admixture evident in all individuals.

Africa↗