The role of Dufour's gland secretions in bees

ABSTRACT. Dufour's gland of bees is often hypertrophied and an extremely rich source of diverse natural products. In the ground-dwelling bees the secretion is mostly used for lining the brood cell with a hydrophobic lining. Whereas in several species the secretion is smeared on the cell walls without any modification, in others the hydrophobic lining is formed only after a chemical transformation of the secretion. The diversity of the chemical means by which hydrophobicity of the brood cells is achieved suggests that it has evolved repeatedly in the bees. In addition to lining their brood cells, several species use Dufour's gland secretion to mark their nest entrance. Analyses of single glands from various species reveal that each bee possesses its own individual composition, expressed in specific relative amounts of each component. Interestingly in the social halictid Evylaeus malachurum , nestmates (considered as sisters) are more similar to each other than non-related bees. The possible functional evolution of the glandular exudate from structural functions to communication and its implications for our understanding of eusociality in bees, is discussed.     

Pattern learning by honey bees

Honey bees learn to recognize flowers on the basis of their odour, colour, and pattern. Previous work had suggested that a flower's pattern is remembered by virtue of several abstract parameters such as spatial frequency, rather than as pictures, but the evidence was not conclusive. New experiments strongly suggest that bees can remember patterns as low-resolution pictures; the resolution is roughly 10°. Control experiments further indicate that flower learning can also involve conditioned inhibition.     

Direct effect of acaricides on pathogen loads and gene expression levels in honey bees Apis mellifera

The effect of using acaricides to control varroa mites has long been a concern to the beekeeping industry due to unintended negative impacts on honey bee health. Irregular ontogenesis, suppression of immune defenses, and impairment of normal behavior have been linked to pesticide use. External stressors, including parasites and the pathogens they vector, can confound studies on the effects of pesticides on the metabolism of honey bees. This is the case of Varroa destructor, a mite that negatively affects honey bee health on many levels, from direct parasitism, which diminishes honey bee productivity, to vectoring and/or activating other pathogens, including many viruses. Here we present a gene expression profile comprising genes acting on diverse metabolic levels (detoxification, immunity, and development) in a honey bee population that lacks the influence of varroa mites. We present data for hives treated with five different acaricides; Apiguard (thymol), Apistan (tau-fluvalinate), Checkmite (coumaphos), Miteaway (formic acid) and ApiVar (amitraz). The results indicate that thymol, coumaphos and formic acid are able to alter some metabolic responses. These include detoxification gene expression pathways, components of the immune system responsible for cellular response and the c-Jun amino-terminal kinase (JNK) pathway, and developmental genes. These could potentially interfere with the health of individual honey bees and entire colonies.     

Processing of sun-azimuth information by honey bees

The dance language of honey bees (Apis mellifera) indicates with good accuracy the distance and direction of a food source. When the direction of a food source is moved, however, the dances of returning foragers indicate the former location rather than the new direction just visited. After subsequent trips the dancers slowly accommodate to the change, and full compensation is achieved only after about 40 min. These and other equally curious results suggest that a running-average processing system may be at work in honey bee navigation.     

Sterility in honey bees caused by dimethyl sulfoxide

Honey bee (Apis mellifera) semen was treated as follows: diluted in saline with 10 percent dimethyl sulfoxide (DMSO) and stored at -196 degrees C; same treatment but stored at 12 degrees C; diluted in saline and stored at 12 degrees C; and undiluted, unstored semen. Daughters (queens) produced from the treated spermatozoa were evaluated for total sterility. Only sterile eggs were produced from 3 percent of the queens in both groups that had DMSO (5/166 in group 1, and 6/234 in group 2). They were different (P less than 0.05) from groups 3 and 4 in which no queens were produced that laid only sterile eggs (0/151 and 0/137, respectively). These results demonstrate that, under the conditions used, a low level of sterility is induced by DMSO, and this F1 sterility raises questions about possible genetic damage by DMSO.     

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.     

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.     

Differential circular RNAs expression in ovary during oviposition in honey bees

Circular RNAs (circRNAs) are non-coding RNAs newly identified and play important roles in RNA regulation. The mechanism and function of circRNAs have been reported in some species. However, little is known regarding circRNAs in honey bees. In this study, we analyzed circRNAs through bioinformatics, and predicted 12,211 circRNAs in the ovary of honey bee queens. 1340, 175 and 100 circRNAs were differentially expressed in comparisons of egg-laying queens vs virgin queens, egg-laying inhibited queens vs egg-laying queens and egg-laying recovery queens vs egg-laying inhibited queens. Further, functional annotation of differentially expressed circRNAs revealed several pathways that are closely related to ovary activation and oviposition, including insulin secretion and calcium signaling pathways. Moreover, the potential interactions among circRNAs, miRNAs, lncRNAs and mRNAs were investigated. Ame_circ_0005197 and ame_circ_0016640 were observed to sponge several reproductive related miRNAs. These findings demonstrate that circRNAs have potential effects in ovary activation and oviposition of honey bees.     

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.     

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.