Changes in weight of the pharyngeal gland and haemolymph titres of juvenile hormone,protein and vitellogenin in worker honey bees

Four physiological parameters (haemolymph-juvenile hormone titre, protein concentration, vitellogenin concentration, and pharyngeal gland dry weight) were examined in the following categories of queenright adult worker bees: summer bees 1–40 days old, winter bees 80–130 days old, 12–100-day old bees at the beginning of winter, 100–195-day old bees at the end of winter, and 1–100-day old bees experimentally induced to live longer in summer.In contrast to the continuously increasing titre of juvenile hormone in ageing summer bees, winter bees kept a constant low level. In bees at the beginning of winter, the hormone titre never reached high values. However, at the end of winter it rose from a low to a high level, comparable with the high titre of 24–40-day old summer bees. In experimentally induced longlived bees in summer, the juvenile hormone titre did not increase as in normal summer bees but remained low as in bees at the beginning of winter. Among the known natural juvenile hormones, only juvenile hormone III was present in the haemolymph of winter bees.The results support the hypothesis of polyphenism being regulated by the titre of juvenile hormone in the haemolymph.     

Nesting aggregation as a predictor of brood parasitism in mason bees (Osmia spp.)

1. Parasitism can be an important source of mortality for insect populations; however, we know little about the factors influencing vulnerability of wild bees to parasites. Mason bees (genus Osmia; Hymenoptera: Megachilidae) are important pollinators of crops and wild plants and are vulnerable to attack by brood parasites. High nest densities may increase rates of brood parasitism by attracting disproportionate numbers of parasites. 2. Three years of field observations from multiple sites were analysed to assess whether mason bee brood parasitism increased with host density. Mason bees were allowed to nest in artificial nesting blocks and establish natural variation in nesting density. Nest cells constructed by bees were checked for the presence of parasite eggs. 3. Parasitism of nest cells strongly increased with the number of actively nesting bees at a nesting block. Mason bees showed no preference for nesting in blocks that were occupied or unoccupied by other mason bees. Parasitism also increased with the number of days a nest was provisioned and decreased over the course of the season. Nest cells constructed last in a nest were significantly more parasitised than inner cells, despite being sealed against invasions. 4. These findings show positively density‐dependent parasitism in mason bees. They also suggest that bees terminate parasitised nests, causing parasitised cells to become outermost nest cells – a behaviour that may represent a defence against parasites. Our results have implications for the management of mason bees as agricultural pollinators, as cultivating them at high densities could reduce offspring survival.     

Changes of RNA virus infection rates and gut microbiota in young worker Apis mellifera (Hymenoptera: Apidae) of a chalkbrood-infected colony after a pollination task in a greenhouse

Western honey bee (Apis mellifera Linnaeus) populations recently have been in decline worldwide owing not only to colony collapse disorder but also other infectious diseases. The problem is neither decreasing nor has it been resolved. Chalkbrood (Ascosphaera apis, Maassen ex Claussen) is a well-known fungal brood disease that is now found throughout the world, and there are indications that the incidence of chalkbrood may be on the rise. Here, we conducted comparative studies to analyze infection rates of pathogenic RNA viruses and gut microbiota of young worker honey bees in two colonies: a healthy control colony raised in an open field and a test colony showing the chalkbrood symptom after a 2-month pollination task in a strawberry greenhouse. We found that the number of young worker bees with deformed wing virus (DWV) RNA was significantly elevated in the chalkbrood-infected colony, and two kinds of gut γ-proteobacteria, Frischella perrara gen. nov. and Pasteurellaceae bacterium Trm1, were especially increased in DWV-infected animals. These results showed that the DWV infection rates of worker honey bees were enhanced when their brood was infected with chalkbrood disease and that the gut microbiota in worker bees was significantly affected by the virus infection.     

Worker life tables, survivorship, and longevity in colonies of Bombus (Fervidobombus) atratus (Hymenoptera: Apidae)

Survivorship curves and longevity of workers were studied in two queenright and two queenless colonies of Bombus (Fervidobombus) atratus. Survivorship curves for workers of all colonies were, in general, convex, indicating an increasing mortality rate with increasing age. The mean longevity for the workers from queenright colonies, 24.3 days and 17.6 days, was not significantly different from that in queenless colonies, 21.2 days and 20.2 days. In all colonies workers started foraging activities when aged 0-5 days, and the potential forager rates rose progressively with increasing age. Mortality rates within each age interval were significantly correlated with the foraging worker rates in all colonies. Only in two of the colonies (one queenright and one queenless) longevity was significantly correlated with worker size. The duration of brood development period seems to be one of the most important factors influencing adult worker longevity in bumble bee species.     

Ecdysteroid titer, ovary status, and dominance in adult worker and queen bumble bees (Bombus terrestris)

The role of ecdysteroids in the regulation of dominance and reproduction in social Hymenoptera is little explored. In the current study we compared ecdysteroid titers in hemolymph of individual queen and worker bumble bees (Bombus terrestris) that differ in their behavior, reproductive status and social environment. Egg-laying queens that head colonies and have ovaries exhibiting all stages of follicle development, had a higher ecdysteroid titer than virgin queens whose ovaries contained only follicles at initial stages. In workers, the relationship between ecdysteroid titers and follicle development appears to be more complex and to be influenced by the bee's social status and social environment. Shortly after emergence, young workers had only follicles at the initial stages of oogenesis and they exhibited a low ecdysteroid titer. No significant correlation was detected between ovary status and ecdysteroid titer in workers, with some workers showing activated ovaries but low ecdysteroid titers. However, at six days of age, a trend towards higher ecdysteroid titer was observed for workers in queenless groups, a condition characterized by rapid follicle development relative to queenright conditions. In these queenless groups, high social status was associated with high ecdysteroid titers. By contrast, in queenright workers ecdysteroid titers were low, even for bees with presumably high social status that had activated ovaries and were observed performing oviposition behavior. This study suggests that ecdysteroids are involved in regulation of reproduction in B. terrestris.     

Small local population sizes and high habitat patch fidelity in a specialised solitary bee

Andrena hattorfiana is a rare solitary bee which has declined during the last decades throughout western Europe. It is specialised to forage pollen from plants of the family Dipsacaceae. Knowledge of distribution, dispersal propensity, and local population sizes is essential for successful conservation of A. hattorfiana. The investigated local bee populations (n = 78) were dominated by small local populations and 60% were smaller than 10 female individuals and 80% were smaller than 50 female individuals. The area of the median occupied habitat patch was 1.25 hectare and harboured 7 female bees. Mark-release-recapture studies of female A. hattorfiana revealed a sedentary behaviour. Among pollen-foraging female bees the average registered distance moved was 46 m. The patch emigration rate was about 2%, with an observed maximum colonization distance of 900 m. Only 10% of the individuals crossed areas without the pollen plant within grassland patches, such as unpaved roads, stone walls and small tree-stands, even if these areas were less than 10 m wide. This study shows that solitary bees can occur in local populations of extremely small size and they have a sedentary behaviour. These are features that usually increase the risk of local population extinction.     

Identification of vitellogenin in the ant, Camponotus festinatus: changes in hemolymph proteins and fat body development in workers.

Vitellogenin has been identified in the ant Camponotus festinatus, both in queens and workers. In the workers, it is already present before adult eclosion in low concentrations (less than 1 microgram/microliter hemolymph). Vitellogenin and vitellin are immunologically identical and are composed of a single type of apoprotein with an apparent Mr = 185,000. The molecular weight of the native molecules was estimated as approximately 460,000 by pore limiting gradient electrophoresis. Vitellogenin was detected as a major protein in the hemolymph of young workers, both under queenright and queenless conditions. Thus, in spite of their sterility in the presence of the queen, C. festinatus workers are able to synthetize vitellogenin which is identical both in size and immunologically to the queen vitellogenin. About 6-7 weeks after adult eclosion, however, vitellogenin was usually undetectable in the hemolymph of queenright workers, particularly the minor workers, while it constituted about 30% of total protein in queenless workers. Protein concentration in the hemolymph of queenless insects increased up to 20-fold as compared to 1-day-old insects. Queenless workers also developed large amounts of perivisceral fat body, while queenright workers, particularly the minor workers, showed a dramatic fat body regression about 6 weeks after emergence.     

Effects of black mustard population size on the taxonomic composition of pollinators

In plant species that are pollinated by a variety of animal species, spatial and temporal variability in the taxonomic composition of those pollinators may cause spatial and temporal variability in selection on floral traits. While temporal variation in pollinator composition has been widely reported, spatial variability, particularly on a local scale, has been studied less frequently; nevertheless, available evidence suggests that local spatial variability may be a widespread feature of plant-pollinator interactions. In addition, the causes of this spatial variability are poorly known. This study was undertaken to quantify variability in the taxonomic composition of pollinators visiting local populations of black mustard, Brassica nigra, and to determine some of the causes of this variability. Simultaneous observations were conducted in seven pairs of black mustard populations. The members of each pair were in close spatial proximity but differed in number of plants. Larger plant populations were visited by significantly greater numbers of honey bees and significantly fewer small bees than small populations on a per-plant basis. There was also a trend toward greater syrphid fly visitation in small populations. The increased numbers of honey bees at large plant populations is probably due to their ability to recruit long distances to the most rewarding plant populations. The lower number of small bees at large plant populations may be due to competition from honey bees and/or spreading a constant number of small bees over the larger number of plants in large populations.This paper is dedicated to the memory of George Eickwort     

Interspecific and conspecific colony mergers in the dwarf honey bees Apis andreniformis and A. florea

The dwarf honey bees Apis florea and A. andreniformis are sympatric in southeast Asia. We translocated eight A. florea colonies and four A. andreniformis colonies to an orchard near Sai Yoke, Thailand. After 2 days, we dequeened half of the colonies. Microsatellite genotyping showed that a queenless A. florea colony merged with a queenright A. florea colony, and a queenless A. andreniformis colony merged with a queenright A. florea colony. The inter-specific merger in particular shows that colonies can combine without direct kin benefits, and that colony mergers probably arise through strong queen attraction.     

The multiplication and spread of sacbrood virus of bees

Sacbrood virus multiplied without causing symptoms in adult bees when it was injected into them or when it was fed to young individuals. More virus accumulated in heads of infected bees than elsewhere in their bodies, and much was in their hypopharyngeal glands. The extract of each infected head contained about 10²medial lethal doses (LD 50s) of sacbrood virus for larvae when given in their food. The infective dose of sacbrood virus by injection for adults was about 10^-4of the LD 50 in food for larvae. The infective dose by mouth for adults was about 10²LD 50s for larvae, but bees older than 4–8 days could not be infected this way. Infection did not spread between adults but is probably transmitted in nature from infected adults to larvae and back to young adults that ingest remains of larvae killed by sacbrood. The youngest adult bees infected with sacbrood ate little pollen and lived only about 3 weeks in the laboratory, as did bees receiving no pollen, whereas bees fed with ample pollen lived 9 weeks.     

Colony founding and initial nest design of honey bees, Apis mellifera L

Thirty-two colonies of bees with varying populations were established in 1·2-m³ boxes for 24 days. At the end of this time, the bees were killed, and the comb structure, design, and placement were examined to obtain information about the initiation of bee nests. The analysis of variance of three dimensions of the comb (height, width, and length) showed no statistical differences when all thirty-two colonies were considered as a group.Comb built by queenless bees differed from any described in the literature. We think it is comb characteristically built by queenless bees that is neither worker nor drone in size but intermediate.The occurrence of multiple clusters building comb with and without queen in the same box is recorded but unexplained at present.An explanation is offered for the curl appearing in the lower edges of straight combs.     

Functionality of Varroa-resistant honey bees (Hymenoptera: Apidae) when used in migratory beekeeping for crop pollination

Two types of honey bees, Apis mellifera L. (Hymenoptera: Apidae), bred for resistance to Varroa destructor Anderson & Trueman were evaluated for performance when used in migratory crop pollination. Colonies of Russian honey bees (RHB) and outcrossed bees with Varroa-sensitive hygiene (VSH) were managed without miticide treatments and compared with colonies of Italian honey bees that served as controls. Control colonies were managed as groups which either were treated twice each year against V. destructor (CT) or kept untreated (CU). Totals of 240 and 247 colonies were established initially for trials in 2008 and 2009, respectively. RHB and VSH colonies generally had adult and brood populations similar to those of the standard CT group regarding pollination requirements. For pollination of almonds [Prunus dulcis (Mill.) D.A.Webb] in February, percentages of colonies meeting the required six or more frames of adult bees were 57% (VSH), 56% (CT), 39% (RHB), and 34% (CU). RHB are known to have small colonies in early spring, but this can be overcome with appropriate feeding. For later pollination requirements in May to July, 94-100% of colonies in the four groups met pollination size requirements for apples (Malus domestica Borkh.), cranberries (Vaccinium macrocarpon Aiton), and lowbush blueberries (Vaccinium angustifolium Aiton). Infestations with V. destructor usually were lowest in CT colonies and tended to be lower in VSH colonies than in RHB and CU colonies. This study demonstrates that bees with the VSH trait and pure RHB offer alternatives for beekeepers to use for commercial crop pollination while reducing reliance on miticides. The high frequency of queen loss (only approximately one fourth of original queens survived each year) suggests that frequent requeening is necessary to maintain desired genetics.     

Effectiveness of honey bees in delivering the biocontrol agent Bacillus subtilis to blueberry flowers to suppress mummy berry disease

Honey bees are important pollinators of commercial blueberries in the southeastern United States, and blueberry producers often use supplemental bees to achieve adequate fruit set. However, honey bees also vector the plant pathogenic fungus Monilinia vaccinii-corymbosi which infects open blueberry flowers through the gynoecial pathway causing mummy berry disease. Here, we report the results of a 3-year field study to test the hypothesis that using bee hives equipped with dispensers containing the biocontrol product Serenade, a commercial formulation of the bacterium Bacillus subtilis which has shown activity against flower infection by M. vaccinii-corymbosi in laboratory experiments, can reduce mummy berry disease incidence when honey bees are used as pollinators in blueberries. Individual honey bees carried 5.1–6.4 × 10⁵ colony-forming units (CFU) of B. subtilis when exiting hive-mounted dispensers with Serenade. On caged rabbiteye blueberry bushes in the field, population densities of B. subtilis vectored by honey bees reached a carrying capacity of <10³ CFU per flower stigma within 2 days of exposure, and there was a highly significant non-linear relationship between B. subtilis populations per stigma and bee activity, expressed as number of legitimate flower visits per time interval per cage (R = 0.6928, P < 0.0001, n = 32). Honey bee density (1600 or 6400 individuals per 5.8-m³ cage) and Serenade treatment (presence or absence of the product in hive-mounted dispensers) significantly (P < 0.05) affected the incidence of fruit mummification on caged bushes, whereby increasing bee density increased disease incidence and application of Serenade reduced disease levels. Taken together, results of this study suggest that use of a hive-dispersed biocontrol product such as Serenade as a supplement during pollination can reduce the risk of mummy berry disease. This may be a prudent practice that optimizes the benefits to pollination of high bee densities while reducing the associated disease-vectoring risk.     

Seasonal changes in ovarian state in a eusocial halictine bee,Lasioglossum duplex,based on stages of the oldest oocytes in each ovariole (Hymenoptera: Halictidae)

Summary The changes in ovarian activity in the life cycle of the eusocial halictine beeLasioglossum (Evylaeus) duplex (Dalla Torre) was studied in both queens and workers by examining the stages of the terminal follicle in each of the six ovarioles. By this method, ovarian activities of both queens and workers were more quantitatively determined than by observation of gross ovarian features as usually conducted. Queen ovaries clearly exhibited two active periods, corresponding to the spring solitary phase and the summer eusocial phase, with distinctly greater activity in the latter. In ovaries of overwintering queens oosorption of young follicle was observed. Worker ovaries were found more active in orphan than in queenright colonies. The order of ovarian activity obtained from pooled data, summer queens>spring queens>orphan workers>queenright workers, was also recognized by comparison of individual females. Bionomics of the eusocial halictine beeLasioglossum duplex IX. Contribution No. 3107 from the Inst. Low Temp. Sci.     

What the honeybee sees: a review of the recognition system of Apis mellifera

Abstract. For many years, two opposing theories have dominated our ideas of what honeybees see. The earliest proposal based on training experiments was that bees detected only simple attributes or features, irrespective of the actual pattern. The features demonstrated experimentally before 1940 were the disruption of the pattern (related to spatial frequency), the area of black or colour, the length of edge, and the angle of orientation of a bar or grating. Cues discovered recently are the range, and radial and tangential edges, and symmetry, relative to the fixation point, which is usually the reward hole. This theory could not explain why recognition failed when the pattern was moved. In the second theory, proposed in 1969, the bee detected the retinotopic directions of black or coloured areas, and estimated the areas of overlap and nonoverlap on each test pattern with the corresponding positions in the training pattern. This proposal explained the progressive loss of recognition as a test pattern was moved or reduced in size, but required that the bees saw and remembered the layout of every learned pattern and calculated the mismatch with each test image. Even so, the same measure of the mismatch was given by many test patterns and could not detect a pattern uniquely. Moreover, this theory could not explain the abundant evidence of simple feature detectors. Recent work has shown that bees learn one or more of a limited number of simple cues. A newly discovered cue is the position, mainly in the vertical direction, of the common centre (centroid) of black areas combined together. Significantly, however, the trained bees look for the cues mentioned above only in the range of places where they had occurred during the training. These two observations made possible a synthesis of both theories. There is no experimental evidence that the bees detect or re-assemble the layout of patterns in space; instead, they look for a cue in the expected place. With an array of detectors of the known cues, together with their directions, this mechanism would enable bees to recognize each familiar place from the coincidences of cues in different directions around the head.     

Honey Bee Hemocyte Profiling by Flow Cytometry

Multiple stress factors in honey bees are causing loss of bee colonies worldwide. Several infectious agents of bees are believed to contribute to this problem. The mechanisms of honey bee immunity are not completely understood, in part due to limited information about the types and abundances of hemocytes that help bees resist disease. Our study utilized flow cytometry and microscopy to examine populations of hemolymph particulates in honey bees. We found bee hemolymph includes permeabilized cells, plasmatocytes, and acellular objects that resemble microparticles, listed in order of increasing abundance. The permeabilized cells and plasmatocytes showed unexpected differences with respect to properties of the plasma membrane and labeling with annexin V. Both permeabilized cells and plasmatocytes failed to show measurable mitochondrial membrane potential by flow cytometry using the JC-1 probe. Our results suggest hemolymph particulate populations are dynamic, revealing significant differences when comparing individual hive members, and when comparing colonies exposed to diverse conditions. Shifts in hemocyte populations in bees likely represent changing conditions or metabolic differences of colony members. A better understanding of hemocyte profiles may provide insight into physiological responses of honey bees to stress factors, some of which may be related to colony failure.     

The guard honey bee: ontogeny and behavioural variability of workers performing a specialized task

Guarding is a relatively unstudied aspect of honey bee, Apis mellifera L., worker behaviour. The aim of this study was to characterize quantitatively the ontogeny and individual variability of guarding behaviour, the allocation of workers to the guard population in a colony, and the intercolonial variability of guarding behaviour. Guarding is a discrete task performed by a distinct group of workers that are younger than foragers and older than house bees. Workers that guarded initiated the behaviour between the ages of 7 and 22 days. The mean age of the onset of guarding varied; the minimum mean age of guards for a colony was 13·6 days and the maximum was 16·0 days. Workers varied in the length of time they spent as a guard. Most bees guarded for less than 1 days; however, some guarded up to 6 consecutive days. The more time a bee spent guarding during a day the more likely that bee was to guard for more than 1 day. Bees that guarded for more than 1 day also had longer and more frequent individual guarding bouts. All colonies that were studied had guard populations, but not all workers guarded. A relatively small proportion of any age cohort was observed to guard. The percentage of an age cohort that guarded varied among colonies, as did the size of the guard population. Guarding is a specialized task in that few bees guard, but guarding does not appear to require experience because so few bees remained as guards for very long. There was intercolonial variation in all aspects of the ontogeny of guarding and in allocation of workers to guarding. This variation is discussed in the light of other studies of variation in worker behaviour.     

Nosema ceranae in age cohorts of the western honey bee (Apis mellifera)

Nosemaceranae intensity (mean spores per bee) and prevalence (proportion of bees infected in a sample) were analyzed in honey bees of known ages. Sealed brood combs from five colonies were removed, emerging bees were marked with paint, released back into their colonies of origin, and collected as recently emerged (0-3 days old), as house bees (8-11 days old), and as foragers (22-25 days old). Fifty bees from each of the five colonies were processed individually at each collection date for the intensity and prevalence of N. ceranae infection. Using PCR and specific primers to differentiate Nosema species, N. ceranae was found to be the only species present during the experiment. At each collection age (recent emergence, house, forager) an additional sample from the inner hive cover (background bees=BG) of each colony was collected to compare the N. ceranae results of this sampling method, commonly used for Nosema spore quantification, to the samples comprised of marked bees of known ages. No recently emerged bees exhibited infection with N. ceranae. One house bee out of the 250 individuals analyzed (prevalence=0.4%) tested positive for N. ceranae, at an infection level of 3.35×10(6) spores. Infection levels were not statistically different between the recently emerged (mean=0 spores/bee) and house bees (mean=1.34×10(4) spores/bee) (P=0.99). Foragers exhibited the highest prevalence (8.3%) and infection intensity (mean=2.38×10(6) spores/bee), with a range of 0-8.72×10(7) spores in individual bees. The average infection level across all foragers was significantly higher than that of recently emerged bees (P=0.01) and house bees (P=0.01). Finally, the prevalence of Nosema in infected bees was found to be positively correlated with the infection intensity in the sample.     

Primer effect of queen pheromone on juvenile hormone biosynthesis in adult worker honey bees

Juvenile hormone synthesis in adult worker honey bees was measured by an in vitro corpora allata bioassay. Adult queenless workers exhibit higher rates of juvenile hormone biosynthesis than queenright workers. Hormone synthesis is not correlated with the volume of the glands. Extract of queen mandibular glands, applied to a dummy, reduces juvenile hormone biosynthesis in caged queenless workers to the level of queenright workers. The same result was obtained with synthetic (E)-9-oxo-2-decenoic acid, the principal component of the queen mandibular gland secretion. This pheromonal primer effect may function as a key regulating element in maintaining eusocial colony homeostasis. The presence of brood does not affect the hormone production of the corpora allata.Abbreviations BSA bovine serum albumin - CA Corpora allata - JH juvenile hormone - 9-ODA (E)-9-oxo-2-decnoic acid