Costs of reproduction are present but latent in eusocial bumblebee queens.

BACKGROUND: The standard evolutionary theory of ageing proposes that ageing occurs because of a trade-off between reproduction and longevity. Eusocial insect queens exhibit positive fecundity-longevity associations and so have been suggested to be counter-examples through not expressing costs of reproduction and through remodelling conserved genetic and endocrine networks regulating ageing and reproduction. If so, eusocial evolution from solitary ancestors with negative fecundity-longevity associations must have involved a stage at which costs of reproduction were suppressed and fecundity and longevity became positively associated. Using the bumblebee (Bombus terrestris), we experimentally tested whether queens in annual eusocial insects at an intermediate level of eusocial complexity experience costs of reproduction, and, using mRNA-seq, the extent to which they exhibit a remodelling of relevant genetic and endocrine networks. Specifically, we tested whether costs of reproduction are present but latent, or whether a remodelling of relevant genetic and endocrine networks has already occurred allowing queens to reproduce without costs. RESULTS: We experimentally increased queens' costs of reproduction by removing their eggs, which caused queens to increase their egg-laying rate. Treatment queens had significantly reduced longevity relative to control queens whose egg-laying rate was not increased. Reduced longevity in treatment queens was not caused by increased worker-to-queen aggression or by increased overall activity in queens. In addition, treatment and control queens differed in age-related gene expression based on mRNA-seq in both their overall expression profiles and the expression of ageing-related genes. Remarkably, these differences appeared to occur principally with respect to relative age, not chronological age. CONCLUSIONS: This study represents the first simultaneously phenotypic and transcriptomic experimental test for a longevity cost of reproduction in eusocial insect queens. The results support the occurrence of costs of reproduction in annual eusocial insects of intermediate social complexity and suggest that reproductive costs are present but latent in queens of such species, i.e. that these queens exhibit condition-dependent positive fecundity-longevity associations. They also raise the possibility that a partial remodelling of genetic and endocrine networks underpinning ageing may have occurred in intermediately eusocial species such that, in unmanipulated conditions, age-related gene expression depends more on chronological than relative age.

Monitoring Immune Modulation in Season Population: Identifying Effects and Markers Related to Apis mellifera ligustica Honey Bee Health.

Honey bees play a significant role in ecology, producing biologically active substances used to promote human health. However, unlike humans, the molecular markers indicating honey bee health remain unknown. Unfortunately, numerous reports of honey bee collapse have been documented. To identify health markers, we analyzed ten defense system genes in Apis mellifera ligustica honey bees from winter (Owb) and spring (Fb for foragers and Nb for newly emerged) populations sampled in February and late April 2023, respectively. We focused on colonies free from SBV and DWV viruses. Molecular profiling revealed five molecular markers of honey bee health. Of these, two seasonal molecular markers-domeless and spz genes-were significantly downregulated in Owb compared to Nb and Fb honey bees. One task-related marker gene, apid-1, was identified as being downregulated in Owb and Nb compared to Fb honey bees. Two recommended general health markers, SOD and defensin-2, were upregulated in honey bees. These markers require further testing across various honey bee subspecies in different climatic regions. They can diagnose bee health without colony intervention, especially during low-temperature months like winter. Beekeepers can use this information to make timely adjustments to nutrients or heating to prevent seasonal losses.

Highly efficient site-specific integration of DNA fragments into the honeybee genome using CRISPR/Cas9.

Functional genetic studies in honeybees have been limited to transposon mediated transformation and site directed mutagenesis tools. However, site- and sequence-specific manipulations that insert DNA fragments or replace sequences at specific target sites are lacking. Such tools would enable the tagging of proteins, the expression of reporters and site-specific amino acid changes, which are all gold standard manipulations for physiological, organismal, and genetic studies. However, such manipulations must be very efficient in honeybees since screening and crossing procedures are laborious due to their social organization. Here, we report an accurate and remarkably efficient site-specific integration of DNA-sequences into the honeybee genome using clustered regularly interspaced short palindromic repeat/clustered regularly interspaced short palindromic repeat-associated protein 9-mediated homology-directed repair. We employed early embryonic injections and selected a highly efficient sgRNA in order to insert 294 and 729 bp long DNA sequences into a specific locus at the dsx gene. These sequences were locus-specifically integrated in 57% and 59% of injected bees. Most importantly, 21% and 25% of the individuals lacked the wildtype sequence demonstrating that we generated homozygous mutants in which all cells are affected (no mosaicism). The highly efficient, locus-specific insertions of nucleotide sequences generating homozygous mutants demonstrate that systematic molecular studies for honeybees are in hand that allow somatic mutation approaches via workers or studies in the next generation using queens with their worker progeny. The employment of early embryonic injections and screenings of highly efficient sgRNAs may offer the prospect of highly successful sequence- and locus-specific mutations also in other organisms.

Assessment of genetic variation in Apis mellifera jemenitica (Hymenoptera: Apidae) based on mitochondrial Cytochrome Oxidase Subunit II and III.

Morphometric and genetic characterization of many Apis mellifera subspecies are well-documented. A. m. jemenetica occurs naturally in Africa and Asia. In this study, genetic variation of mitochondrial Cytochrome Oxidase II (COII) and III (COIII) were analysed in 133 specimens of the endemic honeybee colonies within Saudi Arabia. The COII gene sequence length was 684 bp comprising nine synonymous (1.3%) and two non-synonymous single nucleotide polymorphisms (SNPs) (0.87%). Five variants of COII were not previously documented, one variant (MT755968) showed an extra restriction site when subjected to type II restriction endonuclease from Arthrobacter protophormiae (Apol) or to Haemophilus influenzae Rf (Hinf1). Changes in COII sequence separated samples into three haplogroups. Whereas, COIII gene sequence length was 780 bp, including 18 synonymous and five non-synonymous SNPs. Furthermore, variation in COII sequence was more informative based on restriction profiles and on amino acid changes compared with COIII gene sequence. Variants of COIII showed identical restriction sites when subjected to type II restriction endonuclease from Deinococcus radiophilus (DraI), and revealed high similarity to African subspecies. Results of this study are very useful in understanding genetic diversity and characterization of A. mellifera subspecies.

Social Behavior, Ovary Size, and Population of Origin Influence Cuticular Hydrocarbons in the Orchid Bee Euglossa dilemma.

AbstractCuticular hydrocarbons (CHCs) are waxy compounds on the surface of insects that prevent desiccation and frequently serve as chemical signals mediating social and mating behaviors. Although their function in eusocial species has been heavily investigated, little is known about the evolution of CHC-based communication in species with simpler forms of social organization lacking specialized castes. Here we investigate factors shaping CHC variation in the orchid bee Euglossa dilemma, which forms casteless social groups of two to three individuals. We first assess geographic variation, examining CHC profiles of males and females from three populations. We also consider CHC variation in the sister species, Euglossa viridissima, which occurs sympatrically with one population of E. dilemma. Next, we consider variation associated with female behavioral phases, to test the hypothesis that CHCs reflect ovary size and social dominance. We uncover a striking CHC polymorphism in E. dilemma spanning populations. In addition, we identify a separate set of CHCs that correlate with ovary size, social dominance, and expression of genes associated with social behavior, suggesting that CHCs convey reproductive and social information in E. dilemma. Together, our results reveal complex patterns of variation in which a subset of CHCs reflect the social and reproductive status of nestmates.

A simulation study of a honeybee breeding scheme accounting for polyandry, direct and maternal effects on colony performance.

BACKGROUND: Efficient breeding programs are difficult to implement in honeybees due to their biological specificities (polyandry and haplo-diploidy) and complexity of the traits of interest, with performances being measured at the colony scale and resulting from the joint effects of tens of thousands of workers (called direct effects) and of the queen (called maternal effects). We implemented a Monte Carlo simulation program of a breeding plan designed specifically for Apis mellifera's populations to assess the impact of polyandry versus monoandry on colony performance, inbreeding level and genetic gain depending on the individual selection strategy considered, i.e. complete mass selection or within-family (maternal lines) selection. We simulated several scenarios with different parameter setups by varying initial genetic variances and correlations between direct and maternal effects, the selection strategy and the polyandry level. Selection was performed on colony phenotypes. RESULTS: All scenarios showed strong increases in direct breeding values of queens after 20 years of selection. Monoandry led to significantly higher direct than maternal genetic gains, especially when a negative correlation between direct and maternal effects was simulated. However, the relative increase in these genetic gains depended also on their initial genetic variability and on the selection strategy. When polyandry was simulated, the results were very similar with either 8 or 16 drones mated to each queen. Across scenarios, polyandrous mating resulted in equivalent or higher gains in performance than monoandrous mating, but with considerably lower inbreeding rates. Mass selection conferred a ~ 20% increase in performance compared to within-family selection, but was also accompanied by a strong increase in inbreeding levels (25 to 50% higher). CONCLUSIONS: Our study is the first to compare the long-term effects of polyandrous versus monoandrous mating in honeybee breeding. The latter is an emergent strategy to improve specific traits, such as resistance to varroa, which can be difficult or expensive to phenotype. However, if used during several generations in a closed population, monoandrous mating increases the inbreeding level of queens much more than polyandrous mating, which is a strong limitation of this strategy.

Transcriptome-level assessment of the impact of deformed wing virus on honey bee larvae.

Deformed wing virus (DWV) prevalence is high in honey bee (Apis mellifera) populations. The virus infects honey bees through vertical and horizontal transmission, leading to behavioural changes, wing deformity, and early mortality. To better understand the impacts of viral infection in the larval stage of honey bees, artificially reared honey bee larvae were infected with DWV (1.55 × 1010 copies/per larva). No significant mortality occurred in infected honey bee larvae, while the survival rates decreased significantly at the pupal stage. Examination of DWV replication revealed that viral replication began at 2 days post inoculation (d.p.i.), increased dramatically to 4 d.p.i., and then continuously increased in the pupal stage. To better understand the impact of DWV on the larval stage, DWV-infected and control groups were subjected to transcriptomic analysis at 4 d.p.i. Two hundred fifty-five differentially expressed genes (DEGs) (fold change ≥ 2 or ≤ -2) were identified. Of these DEGs, 168 genes were downregulated, and 87 genes were upregulated. Gene Ontology (GO) analysis showed that 141 DEGs (55.3%) were categorized into molecular functions, cellular components and biological processes. One hundred eleven genes (38 upregulated and 73 downregulated) were annotated by KO (KEGG Orthology) pathway mapping and involved metabolic pathways, biosynthesis of secondary metabolites and glycine, serine and threonine metabolism pathways. Validation of DEGs was performed, and the related gene expression levels showed a similar tendency to the DEG predictions at 4 d.p.i.; cell wall integrity and stress response component 1 (wsc1), cuticular protein and myo-inositol 2-dehydrogenase (iolG) were significantly upregulated, and small conductance calcium-activated potassium channel protein (SK) was significantly downregulated at 4 d.p.i. Related gene expression levels at different d.p.i. revealed that these DEGs were significantly regulated from the larval stage to the pupal stage, indicating the potential impacts of gene expression levels from the larval to the pupal stages. Taken together, DWV infection in the honey bee larval stage potentially influences the gene expression levels from larvae to pupae and reduces the survival rate of the pupal stage. This information emphasizes the consequences of DWV prevalence in honey bee larvae for apiculture.

Assessment of midgut enteroendocrine peptide complement in the honey bee, Apis mellifera.

Peptides modulate physiological/behavioral control systems in all animals. In arthropods, midgut epithelial endocrine cells are one of the largest sources of these signaling agents. At present, little is known about the identity of the peptides that form arthropod midgut enteroendocrine peptidomes. While many techniques can be used for peptide structural identification, in silico transcriptome mining is one that has been used extensively for arthropod neuropeptidome prediction; this strategy has yet to be used for large-scale arthropod enteroendocrine peptide discovery. Here, a tissue-specific transcriptome was used to assess putative enteroendocrine peptide complement in the honey bee, Apis mellifera, midgut. Searches for transcripts encoding members of 42 peptide families were conducted, with evidence of expression for 15 groups found in the assembly: adipokinetic hormone, allatostatin A, allatostatin C, bursicon, CCHamide, CNMamide, diuretic hormone 31, diuretic hormone 44, insulin-like peptide, myosuppressin, neuropeptide F, pigment dispersing hormone, pyrokinin, short neuropeptide F, and tachykinin-related peptide. The proteins deduced from the midgut transcripts are identical in sequence, or nearly so, to those of Apis pre/preprohormones deposited previously into NCBI, providing increased confidence in the accuracy of the reported data. Seventy-five peptides were predicted from the deduced precursor proteins, 26 being members of known peptide families. Comparisons to previously published mass spectrometric data support the existence of many of the predicted Apis peptides. This study is the first prediction of an arthropod midgut peptidome using transcriptomics, and provides a powerful new resource for investigating enteroendocrine peptide signaling within/from the Apis midgut, a species of significant ecological/economic importance.

Rate variation in the evolution of non-coding DNA associated with social evolution in bees.

The evolutionary origins of eusociality represent increases in complexity from individual to caste-based, group reproduction. These behavioural transitions have been hypothesized to go hand in hand with an increased ability to regulate when and where genes are expressed. Bees have convergently evolved eusociality up to five times, providing a framework to test this hypothesis. To examine potential links between putative gene regulatory elements and social evolution, we compare alignable, non-coding sequences in 11 diverse bee species, encompassing three independent origins of reproductive division of labour and two elaborations of eusocial complexity. We find that rates of evolution in a number of non-coding sequences correlate with key social transitions in bees. Interestingly, while we find little evidence for convergent rate changes associated with independent origins of social behaviour, a number of molecular pathways exhibit convergent rate changes in conjunction with subsequent elaborations of social organization. We also present evidence that many novel non-coding regions may have been recruited alongside the origin of sociality in corbiculate bees; these loci could represent gene regulatory elements associated with division of labour within this group. Thus, our findings are consistent with the hypothesis that gene regulatory innovations are associated with the evolution of eusociality and illustrate how a thorough examination of both coding and non-coding sequence can provide a more complete understanding of the molecular mechanisms underlying behavioural evolution. This article is part of the theme issue 'Convergent evolution in the genomics era: new insights and directions'.

Immune related genes as markers for monitoring health status of honey bee colonies.

BACKGROUND: Honey bee population decline threatens the beekeeping sector, agriculture and global biodiversity. Early detection of colony mortality may facilitate rapid interventions to contain and prevent mortality spread. Among others, deformed wing virus (DWV) is capable of inducing colony losses, especially when combined with Varroa destructor mite. Since the bee immune system plays a crucial role in ensuring that bees are able to face these pathogens, we explored whether expression of immune genes could serve as biomarkers of colony health. RESULTS: Herein, we describe a preliminary immunological marker composed of two immune genes (relish and defensin), which provide insight on honey bee antiviral defense mechanism. Of the tested genes, relish expression correlated with the presence of DWV-Varroa complex, while decreased defensin expression correlated with poor resistance to this complex. CONCLUSIONS: The monitoring of these genes may help us to better understand the complex physiology of honey bees's immune system and to develop new approaches for managing the health impacts of DWV infection and varroa infestation in the field.

High sample throughput genotyping for estimating C-lineage introgression in the dark honeybee: an accurate and cost-effective SNP-based tool.

The natural distribution of the honeybee (Apis mellifera L.) has been changed by humans in recent decades to such an extent that the formerly widest-spread European subspecies, Apis mellifera mellifera, is threatened by extinction through introgression from highly divergent commercial strains in large tracts of its range. Conservation efforts for A. m. mellifera are underway in multiple European countries requiring reliable and cost-efficient molecular tools to identify purebred colonies. Here, we developed four ancestry-informative SNP assays for high sample throughput genotyping using the iPLEX Mass Array system. Our customized assays were tested on DNA from individual and pooled, haploid and diploid honeybee samples extracted from different tissues using a diverse range of protocols. The assays had a high genotyping success rate and yielded accurate genotypes. Performance assessed against whole-genome data showed that individual assays behaved well, although the most accurate introgression estimates were obtained for the four assays combined (117 SNPs). The best compromise between accuracy and genotyping costs was achieved when combining two assays (62 SNPs). We provide a ready-to-use cost-effective tool for accurate molecular identification and estimation of introgression levels to more effectively monitor and manage A. m. mellifera conservatories.

The Evolutionary Dynamics of the Odorant Receptor Gene Family in Corbiculate Bees.

Insects rely on chemical information to locate food, choose mates, and detect potential predators. It has been hypothesized that adaptive changes in the olfactory system facilitated the diversification of numerous insect lineages. For instance, evolutionary changes of Odorant Receptor (OR) genes often occur in parallel with modifications in life history strategies. Corbiculate bees display a diverse array of behaviors that are controlled through olfaction, including varying degrees of social organization, and manifold associations with floral resources. Here we investigated the molecular mechanisms driving the evolution of the OR gene family in corbiculate bees in comparison to other chemosensory gene families. Our results indicate that the genomic organization of the OR gene family has remained highly conserved for ∼80 Myr, despite exhibiting major changes in repertoire size among bee lineages. Moreover, the evolution of OR genes appears to be driven mostly by lineage-specific gene duplications in few genomic regions that harbor large numbers of OR genes. A selection analysis revealed that OR genes evolve under positive selection, with the strongest signals detected in recently duplicated copies. Our results indicate that chromosomal translocations had a minimal impact on OR evolution, and instead local molecular mechanisms appear to be main drivers of OR repertoire size. Our results provide empirical support to the longstanding hypothesis that positive selection shaped the diversification of the OR gene family. Together, our results shed new light on the molecular mechanisms underlying the evolution of olfaction in insects.

A Bio-Economic Case Study of Canadian Honey Bee (Hymenoptera: Apidae) Colonies: Marker-Assisted Selection (MAS) in Queen Breeding Affects Beekeeper Profits.

Over the past decade in North America and Europe, winter losses of honey bee (Hymenoptera: Apidae) colonies have increased dramatically. Scientific consensus attributes these losses to multifactorial causes including altered parasite and pathogen profiles, lack of proper nutrition due to agricultural monocultures, exposure to pesticides, management, and weather. One method to reduce colony loss and increase productivity is through selective breeding of queens to produce disease-, pathogen-, and mite-resistant stock. Historically, the only method for identifying desirable traits in honey bees to improve breeding was through observation of bee behavior. A team of Canadian scientists have recently identified markers in bee antennae that correspond to behavioral traits in bees and can be tested for in a laboratory. These scientists have demonstrated that this marker-assisted selection (MAS) can be used to produce hygienic, pathogen-resistant honey bee colonies. Based on this research, we present a beekeeping case study where a beekeeper's profit function is used to evaluate the economic impact of adopting colonies selected for hygienic behavior using MAS into an apiary. Our results show a net profit gain from an MAS colony of between 2% and 5% when Varroa mites are effectively treated. In the case of ineffective treatment, MAS generates a net profit benefit of between 9% and 96% depending on the Varroa load. When a Varroa mite population has developed some treatment resistance, we show that MAS colonies generate a net profit gain of between 8% and 112% depending on the Varroa load and degree of treatment resistance.

Early life stress affects mortality rate more than social behavior, gene expression or oxidative damage in honey bee workers.

Early life stressors can affect aging and life expectancy in positive or negative ways. Individuals can adjust their behavior and molecular physiology based on early life experiences but relatively few studies have connected such mechanisms to demographic patterns in social organisms. Sociality buffers individuals from environmental influences and it is unclear how much early life stress affects later life history. Workers of the honey bee (Apis mellifera L.) were exposed to two stressors, Varroa parasitism and Paraquat exposure, early in life. Consequences were measured at the molecular, behavioral, and demographic level. While treatments did not significantly affect levels of oxidative damage, expression of select genes, and titers of the common deformed wing virus, most of these measures were affected by age. Some of the age effects, such as declining levels of deformed wing virus and oxidative damage, were opposite to our predictions but may be explained by demographic selection. Further analyses suggested some influences of worker behavior on mortality and indicated weak treatment effects on behavior. The latter effects were inconsistent among the two experiments. However, mortality rate was consistently reduced by Varroa mite stress during development. Thus, mortality was more responsive to early life stress than our other response variables. The lack of treatment effects on these measures may be due to the social organization of honey bees that buffers the individual from the impact of stressful developmental conditions.

Developing an in vivo toxicity assay for RNAi risk assessment in honey bees, Apis mellifera L.

Maize plants expressing dsRNA for the management of Diabrotica virgifera virgifera are likely to be commercially available by the end of this decade. Honey bees, Apis mellifera, can potentially be exposed to pollen from transformed maize expressing dsRNA. Consequently, evaluation of the biological impacts of RNAi in honey bees is a fundamental component for ecological risk assessment. The insecticidal activity of a known lethal dsRNA target for D. v. virgifera, the vATPase subunit A, was evaluated in larval and adult honey bees. Activity of both D. v. virgifera (Dvv)- and A. mellifera (Am)-specific dsRNA was tested by dietary exposure to dsRNA. Larval development, survival, adult eclosion, adult life span and relative gene expression were evaluated. The results of these tests indicated that Dvv vATPase-A dsRNA has limited effects on larval and adult honey bee survival. Importantly, no effects were observed upon exposure of Am vATPase-A dsRNA suggesting that the lack of response involves factors other than sequence specificity. The results from this study provide guidance for future RNAi risk analyses and for the development of a risk assessment framework that incorporates similar hazard assessments.

[New SNP markers of the honeybee vitellogenin gene (Vg) used for identification of subspecies Apis mellifera mellifera L].

Preservation of the gene pool of honeybee subspecies Apis mellifera mellifera is of vital importance for successful beekeeping development in the northern regions of Eurasia. An effective method of genotyping honeybee colonies used in modern science is the mapping of sites of single nucleotide polymorphism (SNP). The honeybee vitellogenin gene (Vg) encodes a protein that affects reproductive function, behavior, immunity, longevity, and social organization in the honeybee Apis mellifera and is therefore a topical research subject. The results of comparative analysis of honeybee Vg sequences show that there are 26 SNP sites that differentiate M and C evolutionary branches and can be used as markers in selective breeding, DNA-barcoding, and the creation of genetic passports for A. m. mellifera colonies.

The genomes of two key bumblebee species with primitive eusocial organization.

BACKGROUND: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. RESULTS: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. CONCLUSIONS: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation.

Preliminary characterization of mitochondrial genome of Melipona scutellaris, a Brazilian stingless bee.

Bees are manufacturers of relevant economical products and have a pollinator role fundamental to ecosystems. Traditionally, studies focused on the genus Melipona have been mostly based on behavioral, and social organization and ecological aspects. Only recently the evolutionary history of this genus has been assessed using molecular markers, including mitochondrial genes. Even though these studies have shed light on the evolutionary history of the Melipona genus, a more accurate picture may emerge when full nuclear and mitochondrial genomes of Melipona species become available. Here we present the assembly, annotation, and characterization of a draft mitochondrial genome of the Brazilian stingless bee Melipona scutellaris using Melipona bicolor as a reference organism. Using Illumina MiSeq data, we achieved the annotation of all protein coding genes, as well as the genes for the two ribosomal subunits (16S and 12S) and transfer RNA genes as well. Using the COI sequence as a DNA barcode, we found that M. cramptoni is the closest species to M. scutellaris.

Non-specific dsRNA-mediated antiviral response in the honey bee.

Honey bees are essential pollinators of numerous agricultural crops. Since 2006, honey bee populations have suffered considerable annual losses that are partially attributed to Colony Collapse Disorder (CCD). CCD is an unexplained phenomenon that correlates with elevated incidence of pathogens, including RNA viruses. Honey bees are eusocial insects that live in colonies of genetically related individuals that work in concert to gather and store nutrients. Their social organization provides numerous benefits, but also facilitates pathogen transmission between individuals. To investigate honey bee antiviral defense mechanisms, we developed an RNA virus infection model and discovered that administration of dsRNA, regardless of sequence, reduced virus infection. Our results suggest that dsRNA, a viral pathogen associated molecular pattern (PAMP), triggers an antiviral response that controls virus infection in honey bees.

Altruistic behavior by egg-laying worker honeybees.

If a honeybee (Apis mellifera) colony loses its queen, worker bees develop their ovaries and produce male offspring [1]. Kin selection theory predicts that the degree of altruism in queenless colonies should be reduced because the relatedness of workers to a hivemate's offspring is less in queenless colonies than it is to the daughters of the queen in queenright colonies [2-4]. To explore this hypothesis, we examined the behavior and physiology of queenless egg-laying workers. Queenless bees engaged in both personal reproduction and the social foraging and defense tasks that benefited their colony. Laying workers also had larger brood-food-producing and wax glands, showing metabolic investments in both colony maintenance and personal reproduction. Whereas in queenright colonies there is a very clear age-based pattern of division of labor between workers, in queenless colonies the degree of individual specialization was much reduced. Queenless colonies functioned as a collective of reproductive and behaviorally generalist bees that cooperatively maintained and defended their nest. This social structure is similar to that observed in a number of primitively social bee species [5]. Laying workers therefore show a mix of selfish personal reproduction and altruistic cooperative behavior, and the queenless state reveals previously unrecognized plasticity in honeybee social organization.