Chalkbrood disease in honey bees

Chalkbrood is a fungal disease of honey bee brood caused by Ascosphaera apis. This disease is now found throughout the world, and there are indications that chalkbrood incidence may be on the rise. In this review we consolidate both historic knowledge and recent scientific findings. We document the worldwide spread of the fungus, which is aided by increased global travel and the migratory nature of many beekeeping operations. We discuss the current taxonomic classification in light of the recent complete reworking of fungal systematics brought on by application of molecular methods. In addition, we discuss epidemiology and pathogenesis of the disease, as well as pathogen biology, morphology and reproduction. New attempts at disease control methods and management tactics are reviewed. We report on research tools developed for identification and monitoring, and also include recent findings on genomic and molecular studies not covered by previous reviews, including sequencing of the A. apis genome and identification of the mating type locus.     

Selection for barriers between honey bees and a devastating parasite

Rivaling pesticides and a dearth of flowers, the parasitic mite Varroa destructor presents a tremendous threat to western honey bees, Apis mellifera. A longstanding, but minor, pest for the Asian honey bee Apis cerana, these obligate bee parasites feast on developing and adult A. mellifera across several continents. Varroa reproduction is limited to a short window when developing bee pupae are concealed in wax cells. Mated females target developing bees just before pupation and then have about one day to initiate reproduction, eventually laying one male and up to several female offspring. Female mites often fail to reproduce at all, instead waiting in cells until their bee host finishes development and then hitching dangerous rides on a succession of adult bees for up to several weeks, before scouting for a new host pupa. In this issue of Molecular Ecology, Conlon et al. (2019) have explored mite reproductive success via a clever and thought‐provoking association study. In so doing, they have identified a protein whose actions could be integral to the dance between bees and their mite parasites.     

European foulbrood in honey bees

European foulbrood (EFB) is a severe bacterial brood disease caused by the Gram-positive bacterium Melissocccus plutonius. The disease has a worldwide distribution and is an increasing problem in some areas. Although the causative agent of EFB was described almost a century ago, many basic aspects of its pathogenesis are still unknown. This review presents both historical results and recent molecular data to synthesize present knowledge of this enigmatic honey bee disease.     

Taste perception in honey bees

Taste is crucial for honeybees for choosing profitable food sources, resins, water sources, and for nestmate recognition. Peripheral taste detection occurs within cuticular hairs, the chaetic and basiconic sensilla, which host gustatory receptor cells and, usually a mechanoreceptor cell. Gustatory sensilla are mostly located on the distal segment of the antennae, on the mouthparts, and on the tarsi of the forelegs. These sensilla respond with varying sensitivity to sugars, salts, and possibly amino acids, proteins, and water. So far, no responses of receptor cells to bitter substances were found although inhibitory effects of these substances on sucrose receptor cells could be recorded. When bees are free to express avoidance behaviors, they reject highly concentrated bitter and saline solutions. However, such avoidance disappears when bees are immobilized in the laboratory. In this case, they ingest these solutions, even if they suffer afterward a malaise-like state or even die from such ingestion. Central processing of taste occurs mainly in the subesophageal ganglion, but the nature of this processing remains unknown. We suggest that coding tastants in terms of their hedonic value, thus classifying them in terms of their palatability, is a basic strategy that a central processing of taste should achieve for survival.     

蜜蜂microRNA的研究进展

MicroRNA (miRNA)是一类长度为18~24 nt的内源性非编码小RNA分子,它能通过与靶标mRNA 分子互补结合抑制蛋白质翻译或导致 mRNA 降解,从而调控靶基因表达。蜜蜂是重要的社会性经济昆虫,一直是国际上热门的研究对象。迄今为止,通过各种生物技术在蜜蜂中发现已鉴定注册的miRNA共有218个,对蜜蜂miRNA的研究表明其在蜜蜂的胚胎发育、级型分化、劳动分工和免疫防御等方面可能具有重要的调控作用。本文就miRNA对蜜蜂蜂王和工蜂级型分化、哺育蜂和采集蜂劳动分工、舞蹈行为、脑部神经功能及免疫防御等方面调控作用的最新研究进展进行了综述,以期为进一步研究miRNA提供借鉴和参考。     

Juvenile hormone and aggression in honey bees

We determined whether defense by individual bees against non-nestmates in honey bees (Apis mellifera) is correlated with their juvenile hormone (JH) titers, which are known to vary developmentally and seasonally. We bioassayed winter and summer bees for aggressive and non-aggressive individuals. Bees in winter could not be distinguished by task group, but bees in summer were segregated into nurses and guards. JH titers were correlated with aggressive behavior at two levels. First, winter bees and summer nurses, known to have lower JH titers, both showed less aggression toward foreign bees than did summer guards. Second, aggressive individuals had significantly higher JH titers than did non-aggressive bees within each colony. Inter-colonial variation in aggressiveness was maintained during summer and winter, suggesting a genetic basis for these differences. An alarm pheromone test further substantiated the existence of inter-colonial differences. We found significant variation in JH titers among different colonies, but this variation was not significantly associated with colony-level aggressiveness. The correlation between JH and levels of aggressiveness within a colony suggests a regulatory role for JH, but variation among colonies involves factors other than JH.     

Virus infections in Brazilian honey bees

This work describes the first molecular-genetic evidence for viruses in Brazilian honey bee samples. Three different bee viruses, Acute bee paralysis virus (ABPV), Black queen cell virus (BQCV), and Deformed wing virus (DWV) were identified during a screening of RNAs from 1920 individual adult bees collected in a region of southeastern Brazil that has recently shown unusual bee declines. ABPV was detected in 27.1% of colony samples, while BQCV and DWV were found in 37% and 20.3%, respectively. These levels are substantially lower than the frequencies found for these viruses in surveys from other parts of the world. We also developed and validated a multiplex RT-PCR assay for the simultaneous detection of ABPV, BQCV, and DWV in Brazil.     

Efficacy of the APimicos-B to control and prevent chalkbrood disease in honey bees

Chalkbrood disease in Apis mellifera is a fungal disease affecting developing brood, infested larvae become mummified. As it is a factorial disease, studies on this pathology are obstructed by the need of some predisposing conditions which must occur for such disease to develop. Thus, many questions are yet to be answered about which treatments to apply. The aim of this work is to evaluate the efficacy of the Apimicos-B, a treatment against chalk brood. To induce the disease, some pieces of combs containing susceptible worker brood both from infected and treated colonies and from infected and untreated colonies were cooled. No significant differences were registered (53.12% and 59.58% of mummification respectively).     

Beneficial microorganisms for honey bees: problems and progresses

Nowadays, honey bees are stressed by a number of biotic and abiotic factors which may compromise to some extent the pollination service and the hive productivity. The EU ban of antibiotics as therapeutic agents against bee pathogens has stimulated the search for natural alternatives. The increasing knowledge on the composition and functions of the bee gut microbiota and the link between a balanced gut microbiota and health status have encouraged the research on the use of gut microorganisms to improve bee health. Somehow, we are assisting to the transfer of the “probiotic concept” into the bee science. In this review, we examine the role of the honey bee gut microbiota in bee health and critically describe the available applications of beneficial microorganisms as pest control agents and health support. Most of the strains, mainly belonging to the genera Lactobacillus, Bifidobacterium and Bacillus, are isolated from honey bee crop or gut, but some applications involve environmental strains or formulation for animal and human consumption. Overall, the obtained results show the favourable effect of applied microbial strains on bee health and productivity, in particular if strains of bee origin are used. However, it is actually not yet possible to conclude whether this strategy will ever work. In particular, many aspects regarding the overall setup of the experiments, the dose, the timing and the duration of the treatment need to be optimized, also considering the microbiological safety of the hive products (i.e. pollen and honey). In addition, a deep investigation about the effect on host immunity and physiology is envisaged. Lastly, the final users of the formulations, i.e. beekeepers, should be taken into account for the achievement of high-quality, cost-effective and easy-to-use products.     

蜜蜂级型分化机理

蜜蜂Apis spp.能有效地为多种植物及农作物授粉, 具有重要的经济和生态价值; 蜜蜂作为高度真社会性昆虫, 已成为社会生物学研究的模式生物。社会性昆虫的生殖劳动分工具有重要的进化意义, 而级型分化是形成生殖劳动分工的基础。近年来, 关于蜜蜂级型分化的研究已取得诸多重要成果, 其机理也得到了较为深入的阐释。营养差异引发蜜蜂幼虫的级型分化。蜂王浆中的主要蛋白组分之一--Royalactin是诱导蜂王发育的关键营养因子, 而脂肪体细胞的表皮生长因子受体介导了Royalactin的这种蜂王诱导作用。DNA甲基化是重要的表观遗传机制之一, 且与个体发育和疾病发生紧密相关, 近来的研究表明DNA甲基化在蜜蜂级型分化过程中发挥重要的调控作用。此外, 越来越多的研究进一步深化了人们对内分泌系统调节级型分化作用的认识。本文从关键营养因子调控、 表观遗传调控和内分泌调节3方面综述蜜蜂级型分化的机理, 并对未来的研究提出可能的方向。     

Memory and sun compensation by honey bees

Summary Experiments with two species of honey bees (Apis mellifera andA. cerana) have revealed that bees form a detailed memory of the spatial and temporal pattern of the sun's azimuthal movement, using local landmarks as a reference for the learning. These experiments were performed on overcast days, and consisted of removing a hive from one site in which bees had been trained to find food by flying along a prominent landmark, and displacing it to a similar site in which the landmark was aligned in a different compass direction. On overcast days, bees which flew along the landmark in the new site oriented their waggle dances in the hive as if they had actually flown in the training site. Thus, they confused the two sets of landmarks and set their dance angles according to a memory of the sun's position relative to the original landmarks. Furthermore, the dances changed in correspondence with the sun's azimuthal shift over several hours, even reflecting (approximately) the regular temporal variations in the rate of shift; such features of the sun's course must therefore be stored in memory. The primary mechanism underlying the learning of this pattern is probably similar to that proposed by New and New (1962): bees store in memory several time-linked solar azimuthal positions relative to features of the landscape, and refer to this stored array when they need to determine an unknown azimuth intermediate between two known positions.During the cloudy-day displacement experiments, celestial cues often appeared to bees in the new site, contradicting the stored information on which they had been basing their dances. Although most bees quickly adopted the dance angle reflecting their actual direction of flight relative to the sun, some later reverted to the original dance angle, indicating that the information on which it was based had remained in memory when the new information was being expressed; other bees performed bimodal dances which expressed both sets of information in alternate waggle runs. The separation in memory implied by these behaviors may reflect a neural strategy for updating a previously stored relationship between celestial and terrestrial references with new information presented by seasonal changes in the sun's course or by newly learned landmarks.     

A simple and distinctive microbiota associated with honey bees and bumble bees

Specialized relationships with bacteria often allow animals to exploit a new diet by providing a novel set of metabolic capabilities. Bees are a monophyletic group of Hymenoptera that transitioned to a completely herbivorous diet from the carnivorous diet of their wasp ancestors. Recent culture-independent studies suggest that a set of distinctive bacterial species inhabits the gut of the honey bee, Apis mellifera. Here we survey the gut microbiotae of diverse bee and wasp species to test whether acquisition of these bacteria was associated with the transition to herbivory in bees generally. We found that most bee species lack phylotypes that are the same or similar to those typical of A. mellifera, rejecting the hypothesis that this dietary transition was symbiont-dependent. The most common bacteria in solitary bee species are a widespread phylotype of Burkholderia and the pervasive insect associate, Wolbachia. In contrast, several social representatives of corbiculate bees do possess distinctive bacterial phylotypes. Samples of A. mellifera harboured the same microbiota as in previous surveys, and closely related bacterial phylotypes were identified in two Asian honey bees (Apis andreniformis and Apis dorsata) and several bumble bee (Bombus) species. Potentially, the sociality of Apis and Bombus species facilitates symbiont transmission and thus is key to the maintenance of a more consistent gut microbiota. Phylogenetic analyses provide a more refined taxonomic placement of the A. mellifera symbionts.     

Do competing honey bees matter? Dynamics and abundance of native bees before and after honey bee invasion

To provide replicate samples of local bee populations in a nature preserve, light traps operated continuously on Barro Colorado Island (BCI), Panama, collected bees for 17 years, including 10 years following invasion by African Apis mellifera. Honey bees appeared in light traps as the first swarms colonized the Panama Canal area. Their numbers followed seasonal trends shown in inde-pendent studies, thus indicating bee abundance and activity in a large area. No measurable population-level impact of competition between this invading honey bee and native bees, despite many demonstrations of resource competition at flower patch and colony levels, changed annual abundances of all 15 native bee species. Native bee abundance did not decrease, nor did native bees show substantial reciprocal yearly change with honey bee abundance. One strong negative correlation of bee catches with an extremely rainy year was found. However, multiple regression using rainfall and honey bee abundance as the independent variables showed that neither was responsible for bee population change over 17 years. Nearly half the native species declined during a year that displayed peak honey bee number. That competition from honey bees on an island the size of BCI was necessarily reduced below impact levels expected on the mainland is discussed using a model of resource and consumer density, foraging range, and island size.