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.