Habitat Changes Result in Detrimental Stress Responses in Honey Bees

Morimoto, T., Kojima, Y., Toki, T., Komeda, Y., Yoshiyama, M., Kimura, K., Nirasawa, K. & Kadowaki, T.  2011.  The habitat disruption induces immune-suppression and oxidative stress in honey bees.  Ecology and Evolution 1(2):  201-217.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3287300/

                In their 2011 study, Morimoto et al. demonstrated the effects of long term pollination for agricultural purposes on honey bee hive health.  These domesticated honey bees are kept within a synthetic ecosystem of a greenhouse containing various flowering crop plants including strawberries, watermelons, and eggplants.  The status of worker bees within the hive is a prime indicator of the health of the entire colony.  Honey bee hives are susceptible to various viruses, bacteria, pesticides, and other pathogens.  Under conditions of limited spatial availability like greenhouses, worker bees often die earlier than in a natural setting which could be correlating to higher instances of infection by various pathogens.  Not only are bees more prone to infection, but Morimoto et al. 2011 hypothesize distinct genetic changes will occur that can be demonstrated via microarray.  If the worker bees cannot remain vital, the colony will also suffer and eventually collapse.  Although these honey bees exist in a limited space in Japan, the 2011 study by Morimoto et al. is applicable to domesticated honey bee use for any agricultural pollination.

                Morimoto et al. 2011 set up four different test hives in various locations within greenhouses that contained either strawberries or eggplants.  These test hives were allowed to persist for more than five months while extensive testing on environmental condition and individual honey bees was performed.  Samples were collected every two weeks, and worker bees were harvested in order to perform DNA microarray and quantitative RT-PCR analyses (defined below).  The colonies were weighed and assessed for health at each of the two week intervals.  In order to test for consistency, four additional hives were tested the following year following the same methodology.

                Over the course of the experiments, several significant effects were observed within the colonies.  Among all four colonies, weight loss (entire colony weight) was measured to be from 30-40% or more.  The age and make-up of the fifty, randomly selected worker bees complicated the genetic analyses in the study, but significant results were still obtained.  Using a principle component analysis (PCA), Morimoto et al. 2011 were able to analyze the more than 200,000 data points.  Compared to bees in eggplant greenhouses, bees in strawberry greenhouses exhibited significantly higher differential gene expression.  These expression levels also increased in variability at later collection dates as the colonies persisted and aged.  However, the later data points tended to become synonymous regardless of greenhouse type.  This data inferred that agricultural use of honey bees causes the same differential expression of genes on a long term scale.  These differential gene expression patterns are also correlated with shorter longevity in worker bee lifespan and, therefore, shorter lifespan of the entire colony.  Although Japan uses primarily greenhouses for agriculture, these results are applicable to farms that use honey bees for pollination all over the globe.  Alternative methods and treatments for sustaining healthy honey bee colonies must be attained before honey bees can continue to thrive as agricultural pollinators.

Definitions

DNA microarray- A DNA microarray is a dot matrix which allows easy identification of the expression of various genes.

Quantitative RT-PCR-  Real time polymerase chain reactions are intended to ‘work up’ genetic sequences via the steps of denaturing, annealing, and extension.  Scientists can take a bee’s DNA and create more of it via the use of a primer template.

Honey Bee Pollination Enhances Bean Crop Productivity

Rizzardo, R. A. G., Milfont, M. O., Da Silva, E. M. S., & Freitas, B. M.  2012.  Apis mellifera pollination improves agronomic productivity of anemophilous castor bean (Ricinus communis).  Anais da Academia Brasileira de Ciências 84(4):  1137-1145.

http://www.ncbi.nlm.nih.gov/pubmed/22990600

                In their 2012 study, Rizzardo et al. observed pollination pathways of castor beans and recorded various degrees of productivity outcomes.  Castor beans are a major agricultural product harvested for their high oil content for the synthesis of biodiesel.  The primary method of pollination for castor beans, Ricinus communis, is self-pollination, but it can also be supplemented by wind pollination to neighboring plants and biotic pollination with insect species; primarily the honey bee, Apis mellifera.  Rizzardo et al. 2012 focused their study on the effects of A. mellifera pollination.  These methods include a primary function:  direct pollen transfer from male stamens to female pistils on alternate plants, and a secondary function:  the indirect pollen aggravation upon honey bee visits allowing stamens to more adequately release pollen for self-pollination or wind pollination.  The study team hypothesized that beans pollinated with biotic pollinators would be more productive compared to beans pollinated without the presence of honey bees.  The Rizzardo et al. 2012 study was conducted in Piaui, Brazil, but, although these were South American plants, the castor bean is also a major agricultural product of North America.  Therefore, the results of the study are applicable to agricultural methods intercontinentally.

In Piaui, Brazil, Rizzardo et al. 2012 observed a 3150 hectare castor bean plantation during the months May to June 2006.  Eighteen plots were organized into equal rectangular areas and lettered alternately A through V without the letters N, Q, and R.  The plots were surrounded with unplanted lands, and the entire plantation was encompassed by dense primary forest.  Each plot was subdivided into halves with the treatments of introduction or absence of honey bee populations.  The plots were subsequently observed for productivity of bean count and pollination effectiveness.  The investigators took daily recordings of flower counts (male and female) of each plant, presence of honey bees and other biotic pollinators, and behavioral actions of individual honey bees around the plants.  Plants were also individually treated and measured for production.  Individual plant treatments included methods of ‘bagging’ the plants, hand pollination, biotic pollination, and wind pollination (control).

After their study, Rizzardo et al. 2012 were able to make specific conclusions based on their results.  The primary method of pollination throughout plot areas was self-pollination via gravity or wind facilitation.  The second most common method was biotic pollination by honey bees or other insect species.  The least used method by castor beans for pollination was deemed to be wind pollination amongst neighboring plants.  Although it was not the primary mode, the most productive plants were those that were pollinated by honey bees.  Based on these results, honey bees near crop fields may be an adequate and natural method of augmenting production of agricultural products such as castor beans.  Concessions need to be made to accommodate honey bees.  The use of commercial products such as fertilizers, herbicides, and insecticides would be highly detrimental to honey bee populations.  The installation of honey bee colonies alongside farms could be a safe alternative to decrease the amount of harmful products introduced into ecosystems encompassing commercial farms.

Abnormal Pathogen Levels Characterize Colony Collapse Disorder

VanEngelsdorp, D., Evans, J. D., Saegerman, C., Mullin, C., Haubruge, E., Nguyen, B. K., Frazier, M., Frazier, J., Cox-Foster, D., Chen, Y., Underwood, R., Tarpy, D. R., Pettis, J. S.  2009.  Colony Collapse Disorder: A Descriptive Study.  Public Library of Science ONE 4(8):  1-17.

http://www.ncbi.nlm.nih.gov/pubmed/?term=colony+collapse+disorder%3A++a+descriptive+study

                Colony Collapse Disorder (CCD) is a recently discovered phenomenon associated with three major qualities.  Colonies will have a sharp decline in the numbers of adult honey bee workers.  Contrary to expectations, there will be a lack of dead worker bees in and around the hive.  Also, there is a sharp influx of pest invasion by wax worms as well as kleptoparasitism from healthier hives.  CCD is a communicative disease that typically affects hives during the winter months. In order to gain a more complete understanding of the disease, extensive studies on colonies and their susceptibility are necessitated.

VanEngelsdorp et al. performed studies on CCD colonies in order to characterize the disease, assess risk factors, and gain further insight into the extent and severity.  They monitored commercial hives (healthy, weak, and CCD hives) in 13 apiaries in Florida and California for sixty days in January and February 2007.  91 colonies were observed over the course of the study, and quantitative data were collected regarding the status of each colony.  In a standard commercial colony, honeycomb is expected to cover 90% or more of the hive containment.  Based on this statistic, VanEngelsdorp et al. assumed that 60% coverage characterized a week colony susceptible to CCD infection.  The three identifiable symptoms of CCD discussed previously were used to officially diagnose a colony.  VanEngelsdorp et al. hypothesized that bee colonies deemed to have ongoing CCD will share common risk factors such as pathogen exposure or stress factors.  Risk factors that were measured include several macro-parasites, seven viruses, bacteria, and pesticide susceptibility.  These factors were quantified over the course of the study on CCD hives and tested for correlation to CCD infection.

VanEngelsdorp et al. were able to confirm their hypotheses and ascertain that CCD infection is contagious among hives based on exposure to certain risk factors.  The study was not able to pinpoint an exact causation for CCD.  CCD, however correlated with several factors: pesticide resistance, European Foul Brood (EFB), Kashmir Bee Virus (KBV), and multiple other factors.  With this information, bee farmers can be more aware of the risk factors associated with a disease capable of decimating honey bee populations.  Because bees provide both financial benefits for farmers directly as well as essential pollinator roles for flowering plant species within their ecosystem, it is essential that diseases such as CCD are understood and controlled.  Farmers may utilize additives to bee hives to protect their colonies; the threat of CCD could be eradicated or minimally more properly managed.

Life Spans of Honey Bee Workers Dependent on Colony Size

Rueppell, O., Kaftanouglu, O., & Page Jr., R.E.  2009.  Honey bee (Apis mellifera) workers live longer in small than in large colonies.  National Institutes of Health 44(6-7): 447–452.

http://www.ncbi.nlm.nih.gov/pubmed/19389467

In their 2009 study of European honey bees (Apis mellifera), Rueppell et al. perform a comparative experiment among four colonies determining the longevity of each colony’s worker bees.  The two colonies designated as large colonies are expected to exhibit shorter longevity than the small colonies.  Honey bees are eusocial insects, which causes an interdependency of individuals within the colony.  Because of this high degree of integration, a colony can be viewed as single organism.  However, Rueppell et al. focus on the individual worker bees and their roles within their respective colonies.  They hypothesize that with higher numbers, worker bees from larger colonies are more apt to perform more dangerous tasks to collect food and are therefore more prone to earlier deaths.  The loss of an individual worker bee in a large colony is much less significant compared to a smaller colony based solely on population ratios.  For these reasons, the expectation of higher longevity for worker bees in smaller compared to larger colonies is a valid premise.

                In order to test their hypothesis, Rueppell et al. created four hives of European honey bees that varied significantly in population size.  The experiments were conducted in Tempe, Arizona for three months from May to July 2007.  Two colonies had approximately 4500 individuals, while the larger colonies had approximately 9000 individuals.  These colonies were allowed to persist in hives with glass walls in order to facilitate observation.  For a control to the experiment, 400 and 800 worker bees were introduced to the small and large hives respectively along with 796 tagged worker bees in each hive.  After introduction of the new worker bees, observations of hive building, foraging, and longevity were recorded.  Hive building was measured in square centimeters of newly formed honey comb.  Pollen foraging was determined by the number of marked worker bees which had pollen attached to their corbiculae (pollen baskets).  Longevity was measured from the time of worker bee introduction on the first day to each day thereafter.  If a worker bee did not return to the hive, they were presumed to have died.

                Utilizing chi squared tests and analysis of variance, Rueppell et al. were able to indicate that there was a significant difference between the lifespans of worker bees in small colonies compared to larger colonies.  These results were also graphically represented in survival (number of individuals) over time (days of survival).  [graph included below]  Small colony worker bees were also able to collect more pollen, more efficiently than the larger colony worker bees.  Rueppell et al. were able to confirm their hypothesis regarding comparative longevity in worker honey bees.  These results can be used to gain further understanding of eusocial organisms and their roles with respect to population size.

Graph:  Longevity in honey bee workers cumulative survival over age.