A Common Gut Pathogen Persists in Honey Bees Weakened by Crop Pesticides

Pettis, J. S., Lichtenberg, E. M., Andree, M., Stitzinger, J., Rose, R., & VanEngelsdorp, D.  2013.  Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae.  PLOS ONE 8(7):  1-9.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0070182

                The honey bee plays an integral role in pollination networks of naturally growing angiosperms as well as agricultural crops.  However, bee populations have seen a marked decrease in numbers which can be attributed to a variety of factors.  Most of these factors include contact with non-natural pathogens applied to agricultural crops in recent decades.  Exposure to detrimental compounds can cause immediate death, but can also cause non-lethal problems that affect the hives.  Pesticides and herbicidal chemicals can have deleterious effects on the honey bee immune system, respiratory system, exoskeleton, and digestive system.  Pettis et al. 2013 focus on the effects of pesticides on honey bees causing a vulnerability to the common gut pathogen, Nosema ceranae.  Despite its ordinary nature, Nosema ceranae is not typically widespread among colonies.  However, Pettis et al. 2013 hypothesize that exposure to agricultural pesticides can cause a greater susceptibility among bees to the pathogen.  This hypothesis has a valid premise as pesticides have been proven in other studies to lead to subpar immune function.

                The experiment was conducted at Brushy Mountain Bee Farm in Moravian Falls, North Carolina.  Pettis et al. selected 7 different agricultural plots on the farm containing different flowering crops including:  almond, apple, blueberry, cranberry, cucumber, pumpkin, and watermelon.  Three hives were chosen per plot based on a preliminary data collection recording individual hive flight activity.  The bees tested were owned by the farmers solely for pollination purposes.  Pollen was collected within each of three hives per crop, colligated into one sample per 10 days, sorted based on color and weight, and tested for insecticide, herbicide, and fungicide levels.  Bees exposed to chemicals were then fed Nosema spores and tested for infection.  The data was tested using Kruskal-Wallace, t-tests, and p value tests in order to determine which data were significant.

                47 different types of chemicals including herbicides, fungicides, and insecticides were found in pollen samples.  These chemicals existed at varying levels from trace to multiple lethal doses.  Through their statistical analyses, Pettis et al. were able to determine that both fungicide and herbicide level correlated directly with the onset of infection with Nosema ceranae.  Pesticide load remained consistent regardless of which type of pollen was collected although variety of pesticides varied greatly among plant species.  After being fed Nosema spores, 147 of 630 bees became infected.  8 pesticides were positively correlated with Nosema infection while the remaining 14 had a negative correlation.  These data are integral to modern farming techniques, and more safe pesticides should be applied to crops whenever possible.  Use of better agricultural methods could allow a recovery in honey bee populations.