Publications by authors named "Keith S Delaplane"

19 Publications

  • Page 1 of 1

Persistent effects of management history on honeybee colony virus abundances.

J Invertebr Pathol 2021 Feb 28;179:107520. Epub 2020 Dec 28.

Centre for Ecology and Conservation, University of Exeter, TR10 9FE, UK; Institute of Evolutionary Ecology and Conservation Genomics, University of Ulm, Ulm D-89069, Germany.

Infectious diseases are a major threat to both managed and wild pollinators. One key question is how the movement or transplantation of honeybee colonies under different management regimes affects honeybee disease epidemiology. We opportunistically examined any persistent effect of colony management history following relocation by characterising the virus abundances of honeybee colonies from three management histories, representing different management histories: feral, low-intensity management, and high-intensity "industrial" management. The colonies had been maintained for one year under the same approximate 'common garden' condition. Colonies in this observational study differed in their virus abundances according to management history, with the feral population history showing qualitatively different viral abundance patterns compared to colonies from the two managed population management histories; for example, higher abundance of sacbrood virus but lower abundances of various paralysis viruses. Colonies from the high-intensity management history exhibited higher viral abundances for all viruses than colonies from the low-intensity management history. Our results provide evidence that management history has persistent impacts on honeybee disease epidemiology, suggesting that apicultural intensification could be majorly impacting on pollinator health, justifying much more substantial investigation.
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http://dx.doi.org/10.1016/j.jip.2020.107520DOI Listing
February 2021

Assessing virulence of mites from different honey bee management regimes.

Apidologie 2020 10;51(2):276-289. Epub 2019 Dec 10.

1Department of Environmental Sciences, Emory University, Atlanta, GA 30322 USA.

The mite is an important honey bee parasite that causes substantial losses of honey bee colonies worldwide. Evolutionary theory suggests that the high densities at which honey bees are managed in large-scale beekeeping settings will likely select for mites with greater growth and virulence, thereby potentially explaining the major damage done by these mites. We tested this hypothesis by collecting mites from feral bee colonies, "lightly" managed colonies (those from small-scale sedentary operations), and "heavily" managed colonies (those from large-scale operations that move thousands of colonies across the US on a yearly basis). We established 8 apiaries, each consisting of 11 colonies from a standardized lightly managed bee background that were cleared of mites, and artificially infested each apiary with controlled numbers of mites from feral, lightly managed, or heavily managed bees or left uninoculated as negative control. We monitored the colonies for more than 2 years for mite levels, colony strength (adult bee population, brood coverage, and honey storage), and survival. As predicted by evolutionary theory, we found that colonies inoculated with mites from managed backgrounds had increased mite levels relative to those with mites from feral colonies or negative controls. However, we did not see a difference between heavily and lightly managed colonies, and these higher mite burdens did not translate into greater virulence, as measured by reductions in colony strength and survival. Our results suggest that human management of honey bee colonies may favor the increased population growth rate of , but that a range of potential confounders (including viral infections and genotype-by-genotype interactions) likely contribute to the relationship between mite reproduction and virulence.
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http://dx.doi.org/10.1007/s13592-019-00716-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7175645PMC
December 2019

Industrial bees: The impact of apicultural intensification on local disease prevalence.

J Appl Ecol 2019 Sep 16;56(9):2195-2205. Epub 2019 Jul 16.

Centre for Ecology and Conservation University of Exeter Penryn UK.

It is generally thought that the intensification of farming will result in higher disease prevalences, although there is little specific modelling testing this idea. Focussing on honeybees, we build multi-colony models to inform how "apicultural intensification" is predicted to impact honeybee pathogen epidemiology at the apiary scale.We used both agent-based and analytical models to show that three linked aspects of apicultural intensification (increased population sizes, changes in population network structure and increased between-colony transmission) are unlikely to greatly increase disease prevalence in apiaries. Principally this is because even low-intensity apiculture exhibits high disease prevalence.The greatest impacts of apicultural intensification are found for diseases with relatively low R (basic reproduction number), however, such diseases cause little overall disease prevalence and, therefore, the impacts of intensification are minor. Furthermore, the smallest impacts of intensification are for diseases with high R values, which we argue are typical of important honeybee diseases. Our findings contradict the idea that apicultural intensification by crowding honeybee colonies in large, dense apiaries leads to notably higher disease prevalences for established honeybee pathogens. More broadly, our work demonstrates the need for informative models of all agricultural systems and management practices in order to understand the implications of management changes on diseases.
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http://dx.doi.org/10.1111/1365-2664.13461DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6771535PMC
September 2019

Reduced density and visually complex apiaries reduce parasite load and promote honey production and overwintering survival in honey bees.

PLoS One 2019 23;14(5):e0216286. Epub 2019 May 23.

Department of Biology; Emory University, Atlanta, GA, United States of America.

Managed honey bee (Apis mellifera) colonies are kept at much greater densities than naturally occurring feral or wild colonies, which may have detrimental effects on colony health and survival, disease spread, and drifting behavior (bee movement between natal and non-natal colonies). We assessed the effects of a straightforward apiary management intervention (altering the density and visual appearance of colonies) on colony health. Specifically, we established three "high density / high drift" ("HD") and three "low density / low drift" ("LD") apiary configurations, each consisting of eight bee colonies. Hives in the HD apiary configuration were of the same color and placed 1m apart in a single linear array, while hives in the LD apiary configuration were placed 10m apart at different heights, facing outwards in a circle, and made visually distinctive with colors and symbols to reduce accidental drift between colonies. We investigated disease transmission and dynamics between the apiary configurations by clearing all colonies of the parasitic mite Varroa destructor, and subsequently inoculating two randomly-chosen colonies per apiary with controlled mite doses. We monitored the colonies for two years and found that the LD apiary configuration had significantly greater honey production and reduced overwinter mortality. Inoculation and apiary management intervention interacted to affect brood mite levels, with the highest levels in the inoculated colonies in the HD configuration. Finally, foragers were more than three times more likely to drift in the HD apiary configurations. Our results suggest that a relatively straightforward management change-placing colonies in low-density visually complex circles rather than high-density visually similar linear arrays-can provide meaningful benefits to the health and productivity of managed honey bee colonies.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216286PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6532956PMC
January 2020

Textured Hive Interiors Increase Honey Bee (Hymenoptera: Apidae) Propolis-Hoarding Behavior.

J Econ Entomol 2019 03;112(2):986-990

Department of Environmental Sciences, Emory University, Atlanta, GA.

Numerous papers have shown that propolis contributes favorably to worker honey bee (Apis mellifera L.) immune response and colony social immunity. Moreover, resin-foraging specialists are more sensitive than pollen foragers to tactile information in the nest interior, and they respond to these stimuli by collecting more resin. In this study, we show that in-hive propolis deposition is increased, compared with nonmodified controls, with any one of the three methods for increasing textural complexity of hive wall interior surfaces: 1) plastic propolis trap material stapled to wall interior, 2) parallel saw kerfs cut into wall interior, or 3) roughening wall interior with a mechanized wire brush. Pairwise comparisons showed that propolis deposition was not significantly different among the three textural treatments; however, textural treatments interacted with time to show a more consistent benefit from plastic propolis trap material or roughened interior surface over saw kerfs. Although direct health benefits were not measured, this work shows that it is comparatively simple to increase propolis deposition above background levels by increasing textural stimuli in hive interiors.
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http://dx.doi.org/10.1093/jee/toy363DOI Listing
March 2019

Parasite dispersal risk tolerance is mediated by its reproductive value.

Anim Behav 2017 Oct 14;132:247-252. Epub 2017 Sep 14.

Department of Entomology, University of Georgia, Athens, GA, U.S.A.

Parasite dispersal theory draws heavily upon epidemiological SIR models in which host status (susceptible (S), infected (I), or recovered (R)) is used to study parasite dispersal evolution. In contrast to these extrinsically host-centric drivers, in this study we focus on an intrinsic driver, the parasite's reproductive value (predicted future offspring) as a regulator of the extent to which the individual will engage in risky dispersal behaviour. As a model system we use the honeybee and its ectoparasite, the mite . Mite reproduction happens exclusively inside cells of bee brood, and newly emerged fecund mites may parasitize either a homocolonial brood cell (low risk dispersal) or emigrate to a new bee colony via phoretic attachment to mature forager bees (high risk dispersal). In an empirical bioassay, prepartum mites (high reproductive value) and postpartum mites (low reproductive value) were offered a choice of newly emerged homocolonial worker bees (low risk), homocolonial pollen forager bees (high risk), or heterocolonial pollen foragers (high risk). A preference for newly emerged bees was earlier and more strongly sustained among prepartum mites. This suggests comparatively greater dispersal risk tolerance among postpartum mites with lower reproductive value. A dangerous bid for dispersal may be adaptive if the individual has already successfully reproduced and the rewards for successful dispersal are sufficiently large.
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http://dx.doi.org/10.1016/j.anbehav.2017.08.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5772990PMC
October 2017

Publisher Correction: Ecological and evolutionary approaches to managing honeybee disease.

Nat Ecol Evol 2018 01;2(1):196

Department of Biology, Emory University, Atlanta, GA, 30322, USA.

In the HTML version of this Review originally published, a technical error led to the images in Box 2 being swapped over. This was corrected on 28 August 2017.
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http://dx.doi.org/10.1038/s41559-017-0394-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7609289PMC
January 2018

Ecological and evolutionary approaches to managing honeybee disease.

Nat Ecol Evol 2017 Sep 22;1(9):1250-1262. Epub 2017 Aug 22.

Department of Biology, Emory University, Atlanta, GA, 30322, USA.

Honeybee declines are a serious threat to global agricultural security and productivity. Although multiple factors contribute to these declines, parasites are a key driver. Disease problems in honeybees have intensified in recent years, despite increasing attention to addressing them. Here we argue that we must focus on the principles of disease ecology and evolution to understand disease dynamics, assess the severity of disease threats, and control these threats via honeybee management. We cover the ecological context of honeybee disease, including both host and parasite factors driving current transmission dynamics, and then discuss evolutionary dynamics including how beekeeping management practices may drive selection for more virulent parasites. We then outline how ecological and evolutionary principles can guide disease mitigation in honeybees, including several practical management suggestions for addressing short- and long-term disease dynamics and consequences.
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http://dx.doi.org/10.1038/s41559-017-0246-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5749923PMC
September 2017

Fine scale population genetic structure of , an ectoparasitic mite of the honey bee ().

Apidologie 2016 13;2016:1-9. Epub 2016 Jun 13.

Population Biology, Ecology, and Evolution, Emory University, 400 Dowman Dr, Atlanta, GA 30322; Dept of Environmental Science, Emory University, 400 Dowman Dr, Atlanta, GA 30322.

is an obligate ectoparasitic mite and the most important biotic threat currently facing honey bees (). We used neutral microsatellites to analyze previously unreported fine scale population structure of , a species characterized by extreme lack of genetic diversity owing to multiple bottleneck events, haplodiploidy, and primarily brother-sister matings. Our results surprisingly indicate that detectable hierarchical genetic variation exists between apiaries, between colonies within an apiary, and even within colonies. This finding of within-colony parasite diversity provides empirical evidence that the spread of is not accomplished solely by vertical transmission but that horizontal transmission (natural or human-mediated) must occur regularly.
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http://dx.doi.org/10.1007/s13592-016-0453-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5089174PMC
June 2016

Distance Between Honey Bee Colonies Regulates Populations of at a Landscape Scale.

Apidologie 2016 2;2016:1-9. Epub 2016 May 2.

Department of Entomology, University of Georgia, 413 Biological Sciences Building, Athens, GA 30602 USA.

Inter-colony distance of significantly affects colony numbers of the parasitic mite . We set up 15 apiaries, each consisting of two colonies. Each apiary pair was assigned an inter-colony distance of 0, 10, or 100 m. Colonies were rendered nearly mite-free, then one colony in each pair was seeded with 300 female mites (mite-donor colony), while the other remained uninoculated (mite-recipient colony). After four months of monitoring, a whole model analysis showed that apiaries in which colonies were spaced 100 m apart contained lower average mite numbers than 0 m or 10 m apiaries. There were interactions among colony type, distance, and sampling date; however, when there were significant differences mite numbers were always lower in 100 m apiaries than 10 m apiaries. These findings pose the possibility that Varroa populations are resource regulated at a landscape scale: near-neighbor colonies constitute reproductive resource for mites in the form of additional bee brood.
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http://dx.doi.org/10.1007/s13592-016-0443-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5089168PMC
May 2016

Honey Bee Colonies Headed by Hyperpolyandrous Queens Have Improved Brood Rearing Efficiency and Lower Infestation Rates of Parasitic Varroa Mites.

PLoS One 2015 21;10(12):e0142985. Epub 2015 Dec 21.

Food and Environment Research Agency, Sand Hutton, York, YO41 1LZ, United Kingdom.

A honey bee queen mates on wing with an average of 12 males and stores their sperm to produce progeny of mixed paternity. The degree of a queen's polyandry is positively associated with measures of her colony's fitness, and observed distributions of mating number are evolutionary optima balancing risks of mating flights against benefits to the colony. Effective mating numbers as high as 40 have been documented, begging the question of the upper bounds of this behavior that can be expected to confer colony benefit. In this study we used instrumental insemination to create three classes of queens with exaggerated range of polyandry--15, 30, or 60 drones. Colonies headed by queens inseminated with 30 or 60 drones produced more brood per bee and had a lower proportion of samples positive for Varroa destructor mites than colonies whose queens were inseminated with 15 drones, suggesting benefits of polyandry at rates higher than those normally obtaining in nature. Our results are consistent with two hypotheses that posit conditions that reward such high expressions of polyandry: (1) a queen may mate with many males in order to promote beneficial non-additive genetic interactions among subfamilies, and (2) a queen may mate with many males in order to capture a large number of rare alleles that regulate resistance to pathogens and parasites in a breeding population. Our results are unique for identifying the highest levels of polyandry yet detected that confer colony-level benefit and for showing a benefit of polyandry in particular toward the parasitic mite V. destructor.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0142985PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4686211PMC
June 2016

An Economic Valuation of Biotic Pollination Services in Georgia.

J Econ Entomol 2015 Apr 25;108(2):388-98. Epub 2015 Jan 25.

Department of Entomology, College of Agricultural and Environmental Sciences, University of Georgia, 120 Cedar St., Athens, GA 30602.

As agriculture faces documented decline in bees and other insect pollinators, empirical assessments of potential economic losses are critical for contextualizing the impacts of this decline and for prioritizing research needs. For the state of Georgia, we show that the annual economic value of biotic pollinators is substantial--US$367 million, equivalent to 13 percent of the total production value of crops studied and 3 percent of the total production value of Georgia's agricultural sector. Our unique Geographic Information Systems analysis reveals an irregular pattern of vulnerability. While the Georgia counties displaying the highest economic values of pollination are clustered in southern Georgia, those with the highest dependency on pollinators in terms of their contribution to crop production value are more dispersed throughout the state.
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http://dx.doi.org/10.1093/jee/tou045DOI Listing
April 2015

Pathogens as Predictors of Honey Bee Colony Strength in England and Wales.

PLoS One 2015 17;10(7):e0133228. Epub 2015 Jul 17.

Department of Entomology, University of Georgia, Athens, GA, 30602, United States of America.

Inspectors with the UK National Bee Unit were asked for 2007-2008 to target problem apiaries in England and Wales for pathogen screening and colony strength measures. Healthy colonies were included in the sampling to provide a continuum of health conditions. A total of 406 adult bee samples was screened and yielded 7 viral, 1 bacterial, and 2 microsporidial pathogens and 1 ectoparasite (Acarapis woodi). In addition, 108 samples of brood were screened and yielded 4 honey bee viruses. Virus prevalence varied from common (deformed wing virus, black queen cell virus) to complete absence (Israeli acute paralysis virus). When colonies were forced into one of two classes, strong or weak, the weak colonies contained more pathogens in adult bees. Among observed pathogens, only deformed wing virus was able to predict colony strength. The effect was negative such that colonies testing positive for deformed wing virus were likely to have fewer combs of bees or brood. This study constitutes the first record for Nosema ceranae in Great Britain. These results contribute to the growing body of evidence linking pathogens to poor honey bee health.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0133228PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4506140PMC
May 2016

Nectar minerals as regulators of flower visitation in stingless bees and nectar hoarding wasps.

J Chem Ecol 2014 May 3;40(5):476-83. Epub 2014 Jun 3.

Department of Entomology, University of Georgia, Athens, GA, 30602, USA,

Various nectar components have a repellent effect on flower visitors, and their adaptive advantages for the plant are not well understood. Persea americana (avocado) is an example of a plant that secretes nectar with repellent components. It was demonstrated that the mineral constituents of this nectar, mainly potassium and phosphate, are concentrated enough to repel honey bees, Apis mellifera, a pollinator often used for commercial avocado pollination. Honey bees, however, are not the natural pollinator of P. americana, a plant native to Central America. In order to understand the role of nectar minerals in plant-pollinator relationships, it is important to focus on the plant's interactions with its natural pollinators. Two species of stingless bees and one species of social wasp, all native to the Yucatan Peninsula, Mexico, part of the natural range of P. americana, were tested for their sensitivity to sugar solutions enriched with potassium and phosphate, and compared with the sensitivity of honey bees. In choice tests between control and mineral-enriched solutions, all three native species were indifferent for mineral concentrations lower than those naturally occurring in P. americana nectar. Repellence was expressed at concentrations near or exceeding natural concentrations. The threshold point at which native pollinators showed repellence to increasing levels of minerals was higher than that detected for honey bees. The results do not support the hypothesis that high mineral content is attractive for native Hymenopteran pollinators; nevertheless, nectar mineral composition may still have a role in regulating flower visitors through different levels of repellency.
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http://dx.doi.org/10.1007/s10886-014-0455-8DOI Listing
May 2014

Field-level sublethal effects of approved bee hive chemicals on Honey Bees (Apis mellifera L).

PLoS One 2013 18;8(10):e76536. Epub 2013 Oct 18.

Department of Entomology, University of Georgia, Athens, Georgia, United States of America.

In a study replicated across two states and two years, we tested the sublethal effects on honey bees of the miticides Apistan (tau fluvalinate) and Check Mite+ (coumaphos) and the wood preservative copper naphthenate applied at label rates in field conditions. A continuous covariate, a colony Varroa mite index, helped us disambiguate the effects of the chemicals on bees while adjusting for a presumed benefit of controlling mites. Mite levels in colonies treated with Apistan or Check Mite+ were not different from levels in non-treated controls. Experimental chemicals significantly decreased 3-day brood survivorship and increased construction of queen supercedure cells compared to non-treated controls. Bees exposed to Check Mite+ as immatures had higher legacy mortality as adults relative to non-treated controls, whereas bees exposed to Apistan had improved legacy mortality relative to non-treated controls. Relative to non-treated controls, Check Mite+ increased adult emergence weight. Although there was a treatment effect on a test of associative learning, it was not possible to statistically separate the treatment means, but bees treated with Apistan performed comparatively well. And finally, there were no detected effects of bee hive chemical on colony bee population, amount of brood, amount of honey, foraging rate, time required for marked released bees to return to their nest, percentage of released bees that return to the nest, and colony Nosema spore loads. To our knowledge, this is the first study to examine sublethal effects of bee hive chemicals applied at label rates under field conditions while disambiguating the results from mite control benefits realized from the chemicals. Given the poor performance of the miticides at reducing mites and their inconsistent effects on the host, these results defend the use of bee health management practices that minimize use of exotic hive chemicals.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0076536PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3799823PMC
August 2014

Inorganic nitrogen derived from foraging honey bees could have adaptive benefits for the plants they visit.

PLoS One 2013 29;8(7):e70591. Epub 2013 Jul 29.

Department of Crop & Soil Sciences, the University of Georgia, Athens, Georgia, United States of America.

In most terrestrial ecosystems, nitrogen (N) is the most limiting nutrient for plant growth. Honey bees may help alleviate this limitation because their feces (frass) have high concentration of organic nitrogen that may decompose in soil and provide inorganic N to plants. However, information on soil N processes associated with bee frass is not available. The objectives of this work were to 1) estimate the amount of bee frass produced by a honey bee colony and 2) evaluate nitrogen mineralization and ammonia volatilization from bee frass when surface applied or incorporated into soil. Two cage studies were conducted to estimate the amount of frass produced by a 5000-bee colony, and three laboratory studies were carried out in which bee frass, surface-applied or incorporated into soil, was incubated at 25(o)C for 15 to 45 days. The average rate of bee frass production by a 5,000-bee colony was estimated at 2.27 to 2.69 g N month(-1). Nitrogen mineralization from bee frass during 30 days released 20% of the organic N when bee frass was surface applied and 34% when frass was incorporated into the soil. Volatilized NH3 corresponded to 1% or less of total N. The potential amount of inorganic N released to the soil by a typical colony of 20,000 bees foraging in an area similar to that of the experimental cages (3.24 m(2)) was estimated at 0.62 to 0.74 g N m(-2) month(-1) which may be significant at a community scale in terms of soil microbial activity and plant growth. Thus, the deposition of available N by foraging bees could have adaptive benefits for the plants they visit, a collateral benefit deriving from the primary activity of pollination.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0070591PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3726636PMC
August 2014

Colony Collapse Disorder in context.

Bioessays 2010 Oct 20;32(10):845-6. Epub 2010 Aug 20.

Department of Biology, Dalhousie University, Halifax, NS, Canada; Department of Biology, Acadia University, Wolfville, NS, Canada.

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http://dx.doi.org/10.1002/bies.201000075DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3034041PMC
October 2010

Efficacy of modified hive entrances and a bottom screen device for controlling Aethina tumida (Coleoptera: Nitidulidae) infestations in Apis mellifera (Hymenoptera: Apidae) colonies.

J Econ Entomol 2003 Dec;96(6):1647-52

Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa 6140.

This study was designed to test whether hive entrances reduced with polyvinyl chloride pipe reduce the ingress of Aethina tumida Murray into Apis mellifera L. colonies and whether screen-mesh bottom boards alleviate side effects associated with restricted entrances. Forty-eight colonies distributed equally between two locations each received one of six experimental treatments: 1) conventional solid bottom board and open entrance, 2) ventilated bottom board and open entrance, 3) conventional bottom and 1.9-cm-i.d. pipe entrance, 4) conventional bottom and 3.8-cm pipe entrance, 5) screen bottom and 1.9-cm pipe entrance, and 6) screen bottom and 3.8-cm pipe entrance. Results were inconsistent between apiaries. In apiary 1, colonies with 3.8-cm pipe entrances had fewer A. tuzmida than colonies with open entrances, but this benefit was not apparent in apiary 2. Pipe entrances tended to reduce colony and brood production in both apiaries, and these losses were only partly mitigated with the addition of screened bottom boards. Pipe entrances had no measurable liability concerning colony thermoregulation. There were significantly fewer frames of adult A. mellifera in colonies with 3.8- or 1.9-cm pipe entrances compared with open entrances but more in colonies with screens. There were more frames of pollen in colonies with open or 3.8-cm pipe entrances than 1.9-cm entrances. We conclude that the efficacy of reduced hive entrances in reducing ingress of A. tumida remains uncertain due to observed differences between apiaries. Furthermore, there were side effects associated with restricted entrances that could be only partly mitigated with screened bottom boards.
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http://dx.doi.org/10.1603/0022-0493-96.6.1647DOI Listing
December 2003

Honey bee (Hymenoptera: Apidae) pollination of rabbiteye blueberry Vaccinium ashei var. 'Climax' is pollinator density-dependent.

J Econ Entomol 2003 Aug;96(4):1215-20

Department of Entomology, 463 Biological Sciences Building, University of Georgia, Athens, GA 30602, USA.

In a 2-yr field study, mature orchard plants of rabbiteye blueberry (Vaccinium ashei Reade variety 'Climax'), plus potted pollenizers ('Premier') were caged with varying densities of honey bees (0, 400, 800, 1,600, 3,200, 6,400, or 12,800 bees plus open plot) during the bloom interval. The rate of legitimate flower visits tended to increase as bee density increased within a range of 400-6,400 bees; there were more legitimate visits in cages with 6,400 bees than in those with < or = 1,600 bees. Similarly, within a range of 400-6,400 bees there was a trend for a corresponding increase in fruit-set with means ranging from 25.0 to 79%. Fruit-set was higher in cages with 6,400 or 3,200 bees than in those with < or = 800 bees. Regression analyses showed that fruit-set increased linearly with the rate of legitimate bee visits. Mean weight of berries was unaffected by bee density but varied significantly between years. Within a range of 0-3,200 bees/cage the average seeds per berry tended to increase with increasing bee density; there were more seeds in open plots than in cages with 12,800 honey bees or < or = 1,600 bees. Sucrose content ranged from 12.1 to 16.7% and fruits tended to have more sugar in cages with lower bee densities. Speed of ripening tended to be higher in cages with higher bee densities. Earlier work has shown that the effectiveness of Apis mellifera L. as a pollinator of rabbiteye blueberry is variety-dependent. Our data indicate that the effectiveness of A. mellifera is also bee density-dependent.
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http://dx.doi.org/10.1603/0022-0493-96.4.1215DOI Listing
August 2003
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