Trait Mediated Interactions Affect Honey Bee Foraging

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0075841

Tan, K., Hu, Z., Chen, W., Wang, Z., Wang, Y., & Nieh, J. C.  2013.  Fearful Foragers: Honey Bees Tune Colony and Individual Foraging to Multi-Predator Presence and Food Quality.  Public Library of Science One 8(9): 1-9. 

Trait mediated interactions are indirect predator and prey relationships supplementary to traditional predation.  The fear response of the prey to predators can often cause more widespread effects within an ecosystem.  Tan et al. 2013 explore the role of the presence of predators and food quality on foraging habits of honey bee workers.  Because of the pivotal role of honey bees as pollinators in an ecosystem, predators can cause a cascade effect by decreasing primary producer output indirectly.  Tan et al. 2013 hypothesize that honey bees are deterred from visiting predator occupied flowers and the plants have a decrease in pollination leading to a decrease in seed production.  In order to fully understand the trophic dynamics of ecosystem relationships, trait mediated interactions, not only direct predation, must be measured.

In their 2013 study, Tan et al. studied the proliferation of honey bee pollination during peak hornet season in July to December 2012.  Hornets are known to predate honey bees under natural circumstances, so their indirect effects on honey bees are a viable focal subject for a trophic ecosystem study.  The two hornet species which actively hunt honey bees during this season are V. velutina and V. tropica.  Tan et al. 2013 observed three bee colonies and measured multiple variables in order to determine how the hornets affected pollination habits.  The honey bee workers were collected at the hive entrance and were trained by being taken to an unscented sucrose solution bee feeder.  Honey bees would return to the hive and recruit more workers to collect the solution.  The researchers placed three feeders 30 centimeters apart and treated each feeder with a different treatment:  control, tethered butterfly, and tethered hornet.  Honey bee workers were subsequently observed by their preference of feeder.  In addition to the choice experiments, Tan et al. 2013 also measured the heat-balling predator response for both species of hornets.  Heat-balling is an aggressive defensive response by honey bees to kill predators near the hive by congregating around the offender.

In the heat-balling experiments, honey bees attacked both hornet species, but allocated significantly more mass to killing the larger V. tropica species.  However, in the predation experiments, V. velutina committed significantly more aggressive acts towards pollinating honey bee.  In the colony allocation experiments, significantly more workers were allocated to safe locations (butterfly and control) compared to predator locations (hornet).  Additionally, as predicted, individual bees chose safer foraging sites significantly more than dangerous sites regardless of the richness of fructose.  Lastly, the worker bees spent the most time at safe foraging sites compared to time spent at dangerous sites.  This study conclusively demonstrated the fear response of bees caused a significant effect on foraging strategies.  Despite the predatory hornet being restrained, honey bees were not willing to approach more dangerous feeders.  Predators can exhibit a top down effect on an ecosystem solely by intimidating their prey and triggering avoidance behaviors.

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.