Management of Braula orientalis Örösi (Diptera: Braulidae) in honeybee colonies with tobacco smoke under semiarid conditions

In the present study, bee colonies were smoked with tobacco smoke in order to evaluate the monthly changes in the numbers of worker bees, the infestation rates of worker bees and queens with bee lice, and the annual average honey production per colony. In July of each year, 12 colonies were smoked with tobacco smoke; the remaining hives not smoked with tobacco smoke served as the control. The results indicated that the applications of tobacco smoke during July gave rise to an impressive reduction in the Braula infestation rate on workers (below 1.8%) and reduced the amount of bee lice on the queen to zero throughout the 2–3 months following smoke treatment. In the colonies not treated with smoke, the Braula infestation rates on worker bees started to increase in May and continued to increase constantly during the rest of year, reaching maximum infestation rates of 28.2% and 33.8% in December, with an average of 15 and 17 lice per queen in November in the first and second years, respectively. Worker bee populations peaked in April and July of each year in both treatments. The average honey production per colony was significantly higher in the colonies treated with smoke than those that were not for the first and second years. In conclusion, early summer months may be the crucial time to smoke the colonies with tobacco smoke in order to keep bee lice at low levels for the remaining seasons.     

Effects of Nosema bombi and its treatment fumagillin on bumble bee (Bombus occidentalis) colonies

We examined the effects of Nosema bombi (Microsporidia: Nosematidae) on colonies of bumble bees, Bombus occidentalis Greene (Hymenoptera: Apidae), used to pollinate tomatoes in commercial greenhouses. We assessed methods of detecting N. bombi and tested the effectiveness of fumagillin to control this parasite. N. bombi did not affect adult population size or amount of brood in B. occidentalis colonies. Fumagillin was not effective against N. bombi at the doses we tested, and frass samples did not provide accurate estimates of the intensity of N. bombi infections. The number of N. bombi spores per bee was highly variable among bumble bees within colonies, and accurate estimates could only be obtained by sampling a large proportion of bees in each colony. Therefore, whole bee and frass sampling is useful for determining if N. bombi is present or absent, but not for obtaining accurate estimates of the intensity of N. bombi infections.     

The influence of the vibration signal on worker interactions with the nest and nest mates in established and newly founded colonies of the honey bee, Apis mellifera

Honey bees adjust cooperative activities to colony needs, based in part on information acquired through interactions with the nest and nest mates. We examined the role of the vibration signal in these interactions by investigating the influence of the signal on the movement rates, cell inspection activity, and trophallaxis behavior of workers in established and newly founded colonies of the honey bee, Apis mellifera. Compared to non-vibrated control bees, vibrated recipients in both colony types exhibited increased movement through the nest and greater cell inspection activity, which potentially increased contact with stimuli that enhanced task performance. Also, compared to controls, recipients in both colony types showed increased rates of trophallactic interactions and spent more time engaged in trophallaxis, which potentially further increased the acquisition of information about colony needs. The vibration signal may therefore help to organize labor in honey bees in part by increasing the rate at which workers obtain information about their colony. Vibrated recipients in the established and newly founded colonies did not differ in any aspect of behavior examined, suggesting that colony developmental state did not influence the degree to which individual workers responded to the signal. However, previous work has demonstrated that newly founded colonies have increased levels of vibration signal behavior. Thus, the vibration signal may help to adjust worker activity to colony conditions partly by stimulating greater numbers of bees to acquire information about colony needs, rather than by altering the level at which individual recipients react to the signal. Received 23 October 2006; revised 15 January 2007; accepted 7 February 2007.     

Comparative reproduction of <Emphasis Type="Italic">Varroa destructor</Emphasis> in different types of Russian and Italian honey bee combs

Earlier studies showed that Russian honey bees support slow growth of varroa mite population. We studied whether or not comb type influenced varroa reproduction in both Russian and Italian honey bees, and whether Russian bees produced comb which inhibited varroa reproduction. The major differences found in this study concerned honey bee type. Overall, the Russian honey bees had lower (2.44 ± 0.18%) levels of varroa infestation than Italian honey bees (7.20 ± 0.60%). This decreased infestation resulted in part from a reduced number of viable female offspring per foundress in the Russian (0.85 ± 0.04 female) compared to the Italian (1.23 ± 0.04 females) honey bee colonies. In addition, there was an effect by the comb built by the Russian honey bee colonies that reduced varroa reproduction. When comparing combs having Russian or Italian colony origins, Russian honey bee colonies had more non-reproducing foundress mites and fewer viable female offspring in Russian honey bee comb. This difference did not occur in Italian colonies. The age of comb in this study had mixed effects. Older comb produced similar responses for six of the seven varroa infestation parameters measured. In colonies of Italian honey bees, the older comb (2001 dark) had fewer (1.13 ± 0.07 females) viable female offspring per foundress than were found in the 2002 new (1.21 ± 0.06 females) and 1980s new (1.36 ± 0.08 females) combs. This difference did not occur with Russian honey bee colonies where the number of viable female offspring was low in all three types of combs. This study suggests that honey bee type largely influences growth of varroa mite population in a colony.     

Winter survival of individual honey bees and honey bee colonies depends on level of Varroa destructor infestation

Background

Recent elevated winter loss of honey bee colonies is a major concern. The presence of the mite Varroa destructor in colonies places an important pressure on bee health. V. destructor shortens the lifespan of individual bees, while long lifespan during winter is a primary requirement to survive until the next spring. We investigated in two subsequent years the effects of different levels of V. destructor infestation during the transition from short-lived summer bees to long-lived winter bees on the lifespan of individual bees and the survival of bee colonies during winter. Colonies treated earlier in the season to reduce V. destructor infestation during the development of winter bees were expected to have longer bee lifespan and higher colony survival after winter.

Methodology/Principal Findings

Mite infestation was reduced using acaricide treatments during different months (July, August, September, or not treated). We found that the number of capped brood cells decreased drastically between August and November, while at the same time, the lifespan of the bees (marked cohorts) increased indicating the transition to winter bees. Low V. destructor infestation levels before and during the transition to winter bees resulted in an increase in lifespan of bees and higher colony survival compared to colonies that were not treated and that had higher infestation levels. A variety of stress-related factors could have contributed to the variation in longevity and winter survival that we found between years.

Conclusions/Significance

This study contributes to theory about the multiple causes for the recent elevated colony losses in honey bees. Our study shows the correlation between long lifespan of winter bees and colony loss in spring. Moreover, we show that colonies treated earlier in the season had reduced V. destructor infestation during the development of winter bees resulting in longer bee lifespan and higher colony survival after winter.     

Reproduction of Varroa destructor in worker brood of Africanized honey bees (Apis mellifera)

Reproduction and population growth of Varroa destructor was studied in ten naturally infested, Africanized honeybee (AHB) (Apis mellifera) colonies in Yucatan, Mexico. Between February 1997 and January 1998 monthly records of the amount of pollen, honey, sealed worker and drone brood were recorded. In addition, mite infestation levels of adult bees and worker brood and the fecundity of the mites reproducing in worker cells were determined. The mean number of sealed worker brood cells (10,070 ± 1,790) remained fairly constant over the experimental period in each colony. However, the presence and amount of sealed drone brood was very variable. One colony had drone brood for 10 months and another for only 1 month. Both the mean infestation level of worker brood (18.1 ± 8.4%) and adult bees (3.5 ± 1.3%) remained fairly constant over the study period and did not increase rapidly as is normally observed in European honey bees. In fact, the estimated mean number of mites fell from 3,500 in February 1997 to 2,380 in January 1998. In May 2000 the mean mite population in the study colonies was still only 1,821 mites. The fertility level of mites in this study was much higher (83–96%) than in AHB in Brazil(25–57%), and similar to that found in EHB (76–94%). Mite fertility remained high throughout the entire study and was not influenced by the amount of pollen, honey or worker brood in the colonies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution of <Emphasis Type="Italic">Paenibacillus larvae</Emphasis> Spores Among Adult Honey Bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>) and the Relationship with Clinical Symptoms of American Foulbrood

Knowledge of the distribution of Paenibacillus larvae spores, the causative agent of American foulbrood (AFB), among individual adult honey bees is crucial for determining the appropriate number of adult bees to include in apiary composite samples when screening for diseased colonies. To study spore distribution at the individual bee level, 500 honey bees were collected from different parts of eight clinically diseased colonies and individually analyzed for P. larvae. From the brood chamber and from the super, bees were randomly collected and individually put in Eppendorf vials. The samples were frozen as soon as possible after collection. Concurrently with sampling, each colony was visually inspected for clinical symptoms of AFB. The number of clinically diseased cells in the colony was visually estimated. All samples were cultured in the laboratory for P. larvae. The results demonstrate that the spores are not randomly distributed among the bees; some bees have much higher spore loads than others. It is also clear that as the proportion of contaminated bees increase, the number of spores from each positive bee also increases. The data also demonstrated a relationship between the number of clinically diseased cells and the proportion of positive bees in individual colonies. This relationship was used to develop a mathematical formula for estimating the minimum number of bees in a sample to detect clinical disease. The formula takes into account the size of the apiary and the degree of certainty with which one aims to discover clinical symptoms. Calculations using the formula suggest that adult bee samples at the colony level will detect light AFB infections with a high probability. However, the skewed spore distribution of the adult bees makes composite sampling at the apiary level more problematic, if the aim of the sampling is to locate lightly infected individual colonies within apiaries. The results suggest that false-negative culturing results from composite samples of adult bees from individual colonies with clinical symptoms of AFB are highly improbable. However, if single colonies have light infections in large apiaries, the dilution effect from uncontaminated bees from healthy colonies on the positive bees from diseased colonies may yield false-negative results at the apiary level.     

Varroa-tolerant Italian honey bees introduced from Brazil were not more efficient in defending themselves against the mite Varroa destructor than Carniolan bees in Germany

In Europe and North America honey bees cannot be kept without chemical treatments against Varroa destructor. Nevertheless, in Brazil an isolated population of Italian honey bees has been kept on an island since 1984 without treatment against this mite. The infestation rates in these colonies have decreased over the years. We looked for possible varroa-tolerance factors in six Italian honey bee colonies prepared with queens from this Brazilian island population, compared to six Carniolan colonies, both tested at the same site in Germany. One such factor was the percentage of damaged mites in the colony debris, which has been reported as an indicator of colony tolerance to varroa. A mean of 35.8% of the varroa mites collected from the bottoms of the Italian bee colonies were found damaged, among which 19.1% were still alive. A significantly greater proportion of damaged mites were found in the Carniolan bees (42.3%) and 22.5% were collected alive. The most frequent kind of damage found was damaged legs alone, affecting 47.4% of the mites collected from debris in Italian bees, which was similar to the amount found in Carniolan colonies (46%). The mean infestation rate by the varroa mite in the worker brood cells in the Italian bee colonies was 3.9% in June and 3.5% in July, and in drone brood cells it was 19.3% in June. In the Carniolan honey bee colonies the mean infestation rates in worker brood cells were 3.0 and 6.7%, respectively in the months of June and July and 19.7% in drone brood cells in June. In conclusion, the 'Varroa-tolerant' Italian honey bees introduced from Brazil produced lower percentages of damaged mites (Varroa destructor) in hive debris and had similar brood infestation rates when compared to 'susceptible' Carniolan bees in Germany. In spite of the apparent adaptation of this population of Italian bees in Brazil, we found no indication of superiority of these bees when we examined the proportions of damaged mites and the varroa-infestation rates, compared to Carniloan bees kept in the same apiary in Germany.     

Caste, Sex and Strain of Honey Bees (Apis mellifera) Affect Infestation with Tracheal Mites (Acarapis woodi)*

Worker honey bees from genetic strains selected for being resistant (R) or susceptible (S) to tracheal mites typically show large differences in infestation in field colonies and in bioassays that involve controlled exposure to infested bees. We used bioassays exposing newly emerged individuals to infested workers to compare the propensity for tracheal mites to infest queens, drones and workers from R and S colonies. In tests with queens, newly emerged R and S queens were either simultaneously confined in infested colonies (n = 95 and 87 respectively), or individually caged with groups of 5–20 infested workers (n = 119 and 115 respectively). Mite prevalence (percentage of individuals infested) and abundance (foundress mites per individual) after 4–6 days did not differ between R and S queens. In another test, five newly emerged drones and workers from both an R and an S colony, and a queen of one of the two strains, were caged in each of 38 cages with 20 g of workers infested at 60–96% prevalence. Infestations of the R queens (n = 17) and S queens (n = 19) did not differ significantly, but R workers had half the mite abundance of S workers, while R drones received about a third more migrating mites than S drones. In tests to evaluate possible mechanisms, removal of one mesothoracic leg from R and S workers resulted in 2- to 10-fold increase in mite abundance on the treated side, but excising legs did not affect infestation of the corresponding tracheae in drones. This suggests that differences in infestation between R and S workers, but not drones, are largely determined by their ability to remove mites through autogrooming. If autogrooming is the primary mechanism of colony resistance to tracheal mites, selection for resistance to tracheal mites using infestation of hemizygous drones may be inefficient. *The U.S. Government’s right ot retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

A sequential sampling scheme for detecting infestation levels of tracheal mites (Heterostigmata: Tarsonemidae) in honey bee (Hymenoptera: Apidae) colonies

The introduction of parasitic honey bee mites, the tracheal mite, Acarapis woodi (Rennie) in 1984 and the Varroa mite, Varroa jacobsoni, in 1987, has dramatically increased the winter mortality of honey bee, Apis mellifera L., colonies in many areas of the United States. Some beekeepers have minimized their losses by routinely treating their colonies with menthol, currently the only Environmental Protection Agency-approved and available chemical for tracheal mite control. Menthol is also expensive and can interfere with honey harvesting. Because of inadequate sampling techniques and a lack of information concerning treatment, this routine treatment strategy has increased the possibility that tracheal mites will develop resistance to menthol. It is important to establish economic thresholds and treat colonies with menthol only when treatment is warranted rather than treating all colonies regardless of infestation level. The use of sequential sampling may reduce the amount of time and effort expended in examining individual colonies and determining if treatment is necessary. Sequential sampling also allows statistically based estimates of the percentage of bees in standard Langstroth hives infested with mites while controlling for the possibility of incorrectly assessing the amount of infestation. On the average, sequential sampling plans require fewer observations (bees) to reach a decision for specified probabilities of type I and type II errors than are required for fixed sampling plans, especially when the proportion of infested bees is either very low or very high. We developed a sequential sampling decision plan to allow the user to choose specific economic injury levels and the probability of making type I and type II errors which can result inconsiderable savings in time, labor and expense.     

The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies

Africanized honey bees (Apis mellifera, Hymenoptera: Apidae) in Brazil are tolerant of infestations with the exotic ectoparasitic mite, Varroa destructor (Mesostigmata: Varroidae), while the European honey bees used in apiculture throughout most of the world are severely affected. Africanized honey bees are normally kept in hives with both naturally built small width brood cells and with brood cells made from European-sized foundation, yet we know that comb cell size has an effect on varroa reproductive behavior. Three types (sizes) of brood combs were placed in each of six Africanized honey bee colonies: new (self-built) Africanized comb, new Italian comb (that the bees made from Italian-sized commercial foundation), and new Carniolan comb (built naturally by Carniolan bees). About 100 cells of each type were analyzed in each colony. The Africanized comb cells were significantly smaller in (inner) width (4.84 mm) than the European-sized comb cells (5.16 and 5.27 mm for Italian and Carniolan cells, respectively). The brood cell infestation rates (percentage cells infested) were significantly higher in the Carniolan-sized comb cells (19.3%) than in the Italian and Africanized cells (13.9 and 10.3%, respectively). The Carniolan-sized cells also had a significantly larger number of invading adult female mites per 100 brood cells (24.4) than did the Italian-sized cells (17.7) and the natural-sized Africanized worker brood cells (15.6). European-sized worker brood cells were always more infested than the Africanized worker brood cells in the same colony. There was a highly significant correlation (P<0.01) between cell width and the rate of infestation with varroa in four of the six colonies. The small width comb cells produced by Africanized honey bees may have a role in the ability of these bees to tolerate infestations by Varroa destructor, furthermore it appears that natural-sized comb cells are superior to over-sized comb cells for disease resistance.     

Lower Virus Infections in Varroa destructor-Infested and Uninfested Brood and Adult Honey Bees (Apis mellifera) of a Low Mite Population Growth Colony Compared to a High Mite Population Growth Colony

A comparison was made of the prevalence and relative quantification of deformed wing virus (DWV), Israeli acute paralysis virus (IAPV), black queen cell virus (BQCV), Kashmir bee virus (KBV), acute bee paralysis virus (ABPV) and sac brood virus (SBV) in brood and adult honey bees (Apis mellifera) from colonies selected for high (HMP) and low (LMP) Varroa destructor mite population growth. Two viruses, ABPV and SBV, were never detected. For adults without mite infestation, DWV, IAPV, BQCV and KBV were detected in the HMP colony; however, only BQCV was detected in the LMP colony but at similar levels as in the HMP colony. With mite infestation, the four viruses were detected in adults of the HMP colony but all at higher amounts than in the LMP colony. For brood without mite infestation, DWV and IAPV were detected in the HMP colony, but no viruses were detected in the LMP colony. With mite infestation of brood, the four viruses were detected in the HMP colony, but only DWV and IAPV were detected and at lower amounts in the LMP colony. An epidemiological explanation for these results is that pre-experiment differences in virus presence and levels existed between the HMP and LMP colonies. It is also possible that low V. destructor population growth in the LMP colony resulted in the bees being less exposed to the mite and thus less likely to have virus infections. LMP and HMP bees may have also differed in susceptibility to virus infection.     

Development of early infestations by the miteVarroa jacobsoni in honey-bee (Apis mellifera) colonies in cold climates

The development of an infestation by five to eight introduced adult females ofVarroa jacobsoni Oud. in 35 honey-bee (Apis mellifera L.) colonies was monitored for 16 months with no outside source of infestation. Calculations on the size of the mite populations were based on collection of debris, samples of bees and brood, and estimates of number of bees and broodcells during the summer. In the winter, only dead bees and debris were collected. Samples were taken at 3-week intervals. Data indicated that the mite population probably could increase more than 100 times within one summer, and more than ten times between years, in a climate with a brood-rearing period of less than five months. A large variation in mite population increase existed between colonies. The winter mortality of mites that die with the host or drop from the winter cluster has a large influence on the population dynamics of the mite. Data also indicated that the simple method of counting mites in hive debris is a useful parameter for monitoring the population development ofVarroa in colonies with hatching brood.     

Ontogeny of worker body size distribution in bumble bee (Bombus impatiens) colonies

1. Bumble bees exhibit worker size polymorphisms; highly related workers within a colony may vary up to 10‐fold in body mass. As size variation is an important life history feature in bumble bees, the distribution of body sizes within the colony and how it fluctuates over the colony cycle were analysed. 2. Ten commercially purchased colonies of Bombus impatiens (Cresson) were reared in ad libitum conditions. The size of all workers present and newly emerging workers (callows) was recorded each week. 3. The average size of bumble bee workers did not change with colony age, but variation in body size tended to decrease over time. The average size of callows did not change with population size, but did tend to decrease with colony age. In all measures, there was considerable variation among colonies. 4. Colonies of B. impatiens usually produced workers with normally distributed body sizes throughout the colony life cycle. Unlike most polymorphic ants, there was no increase in worker body size with colony age or colony size. This provides the first, quantitative data on the ontogeny of bumble bee worker size distribution. The potential adaptive significance of this size variation is discussed.     

Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass‐flowering prairie crop

One of the most commonly seeded crops in Canada is canola, a cultivar of oilseed rape (Brassica napus). As a mass‐flowering crop grown intensively throughout the Canadian Prairies, canola has the potential to influence pollinator success across tens of thousands of square kilometers of cropland. Bumble bees (Bombus sp.) are efficient pollinators of many types of native and crop plants. We measured the influence of this mass‐flowering crop on the abundance and phenology of bumble bees, and on another species of social bee (a sweat bee; Halictus rubicundus), by continuously deploying traps at different levels of canola cultivation intensity, spanning the start and end of canola bloom. Queen bumble bees were more abundant in areas with more canola cover, indicating that this crop is attractive to queens. However, bumble bee workers were significantly fewer in these locations later in the season, suggesting reduced colony success. The median collection dates of workers of three bumble bee species were earlier near canola fields, suggesting a dynamic response of colonies to the increased floral resources. Different species experienced this shift to different extents. The sweat bee was not affected by canola cultivation intensity. Our findings suggest that mass‐flowering crops such as canola are attractive to bumble bee queens and therefore may lead to higher rates of colony establishment, but also that colonies established near this crop may be less successful. We propose that the effect on bumble bees can be mitigated by spacing the crop more evenly with respect to alternate floral resources.     

How Honey Bee Colonies Survive in the Wild: Testing the Importance of Small Nests and Frequent Swarming

The ectoparasitic mite, Varroa destructor, and the viruses that it transmits, kill the colonies of European honey bees (Apis mellifera) kept by beekeepers unless the bees are treated with miticides. Nevertheless, there exist populations of wild colonies of European honey bees that are persisting without being treated with miticides. We hypothesized that the persistence of these wild colonies is due in part to their habits of nesting in small cavities and swarming frequently. We tested this hypothesis by establishing two groups of colonies living either in small hives (42 L) without swarm-control treatments or in large hives (up to 168 L) with swarm-control treatments. We followed the colonies for two years and compared the two groups with respect to swarming frequency, Varroa infesttion rate, disease incidence, and colony survival. Colonies in small hives swarmed more often, had lower Varroa infestation rates, had less disease, and had higher survival compared to colonies in large hives. These results indicate that the smaller nest cavities and more frequent swarming of wild colonies contribute to their persistence without mite treatments.     

Daily number of bee louse (Braula coeca) in honey bee (Apis mellifera carnica and A. m. syriaca) colonies maintained under semi‐arid conditions

Experimental work was conducted at two apiaries located in Irbid district and in Shuna North, Jordan, during the years 2004–2006. The aims of these investigations were to estimate the seasonal changes in the infestation rates of the bee louse (Braula sp.) and to develop an easy and rapid method of estimating the infestation rate on workers with bee Braula. Two major honey bee subspecies are reared in Jordan; Apis mellifera carnica and Apis mellifera syriaca were used in this study. The results showed that the infestation rate began to increase rapidly in May, reaching the season's maximum rate of 16.2%, 15.8% and 17.4% for A. m. carnica and 22.6%, 23.9% and 22.9% for A. m. syriaca in December of 2004, 2005 and 2006, respectively. The maximum adult numbers of bees were found in April and June, whereas the minimum for the year was in January in both honey bee subspecies colonies during the study period. The actual population of the bee louse could be estimated by counting the daily dropped lice and multiplying by a factor of 158. This factor is valid for the experimental colonies of both subspecies kept for 3 years under semi‐arid Mediterranean conditions.     

Evidence for emerging parasites and pathogens influencing outbreaks of stress-related diseases like chalkbrood

In agriculture, honey bees play a critical role as commercial pollinators of crop monocultures which depend on insect pollination. Hence, the demise of honey bee colonies in Europe, USA, and Asia caused much concern and initiated many studies and research programmes aiming at elucidating the factors negatively affecting honey bee health and survival. Most of these studies look at individual factors related to colony losses. In contrast, we here present our data on the interaction of pathogens and parasites in honey bee colonies. We performed a longitudinal cohort study over 6 years by closely monitoring 220 honey bee colonies kept in 22 apiaries (ten randomly selected colonies per apiary). Observed winter colony losses varied between 4.8% and 22.4%; lost colonies were replaced to ensure a constant number of monitored colonies over the study period. Data on mite infestation levels, infection with viruses, Nosema apis and Nosema ceranae, and recorded outbreaks of chalkbrood were continuously collected. We now provide statistical evidence (i) that Varroa destructor infestation in summer is related to DWV infections in autumn, (ii) that V. destructor infestation in autumn is related to N. apis infection in the following spring, and most importantly (iii) that chalkbrood outbreaks in summer are related to N. ceranae infection in the preceding spring and to V. destructor infestation in the same season. These highly significant links between emerging parasites/pathogens and established pathogens need further experimental proof but they already illustrate the complexity of the host–pathogen-interactions in honey bee colonies.     

Bumblebee flight distances in relation to the forage landscape

1. Foraging range is a key aspect of the ecology of 'central place foragers'. Estimating how far bees fly under different circumstances is essential for predicting colony success, and for estimating bee-mediated gene flow between plant populations. It is likely to be strongly influenced by forage distribution, something that is hard to quantify in all but the simplest landscapes; and theories of foraging distance tend to assume a homogeneous forage distribution. 2. We quantified the distribution of bumblebee Bombus terrestris L. foragers away from experimentally positioned colonies, in an agricultural landscape, using two methods. We mass-marked foragers as they left the colony, and analysed pollen from foragers returning to the colonies. The data were set within the context of the 'forage landscape': a map of the spatial distribution of forage as determined from remote-sensed data. To our knowledge, this is the first time that empirical data on foraging distances and forage availability, at this resolution and scale, have been collected and combined for bumblebees. 3. The bees foraged at least 1.5 km from their colonies, and the proportion of foragers flying to one field declined, approximately linearly, with radial distance. In this landscape there was great variation in forage availability within 500 m of colonies but little variation beyond 1 km, regardless of colony location. 4. The scale of B. terrestris foraging was large enough to buffer against effects of forage patch and flowering crop heterogeneity, but bee species with shorter foraging ranges may experience highly variable colony success according to location.     

Movement of honey bee (Apis mellifera L.) queen mandibular gland pheromone in populous and unpopulous colonies

The mode of intranest transfer of the honey bee queen mandibular gland pheromone complex (QMP) was investigated in unpopulous and populous, slightly congested colonies, using synthetic QMP containing tritiated 9-keto-2(E)-decenoic acid, one of the QMP components. Radiolabel was rapidly transported from the center to the peripheral regions of the nest, and in a manner consistent with worker to worker transport. Population size and congestion had no effect on the relative rates of movement from the center to the periphery of the nest or on the mean amounts of radiolabel on individual bees. However, a significantly smaller proportion of the workers in the populous colonies received detectable amounts of radiolabel than in the uncongested colonies, and workers carrying especially large amounts of radiolabel were less numerous in the crowded colonies. It is suggested that, at the stage of colony development that the colonies were in, population size has more of an effect on intranest pheromone transmission than does crowding. Interference with pheromone transfer may occur only at higher levels of congestion than were created, and nearer to the reproductive phase of colony development. An alternative hypothesis is that colony crowding does not significantly affect QMP transport and that the onset of reproductive queen rearing may be associated more with changes in worker thresholds of response to QMP.