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.