En-Cheng Yang, Ph.D., is head of the Insect Neurobiology Laboratory at the National Taiwan University in Taipei. His research on honey bees has revealed subtle but worrisome effects of pesticides on bees’ brains. (Photo credit: En-Cheng Yang)

By Constance Lin

Varroa mites, pathogens, or climate change? What exactly causes the honey bee Colony Collapse Disorder (CCD)? Honey bees (Apis mellifera) offer us critical pollination services. In the United Kingdom, for instance, data from the British Beekeepers Association estimates that approximately one-third of the nation’s food supply is dependent on pollination, and more than 70 types of crops are bee-pollinated. Despite whatever changes that may occur in politics, science, or technology, agriculture still remains the most crucial component in sustaining civilization.

Constance Lin

According to a research done in Germany in 2005, every year, a potential agricultural crop loss of nearly 50 percent is caused by pests globally. To maintain fields upon fields of food crops, farmlands become the most prolific users of pesticides. But, pesticides often kill indiscriminately, inadvertently hurting beneficial insects like honey bees.

The research of Professor En-Cheng Yang, Ph.D., from the National Taiwan University may shed some light on how the pesticide imidacloprid contributes to CCD. With training in entomology as well as neuroscience, Yang investigates the neural mechanisms behind insect biology and behavior.

To pinpoint where in relation to the hive CCD is occurring, Yang explains two novel techniques he and his colleagues developed to track honey bees.

“[One of them] is based on a counting system with infrared beams [that we call] the bee counter,” Yang says. “The bee counter [enables us to] monitor the in-and-out activities of foragers in a whole colony without marking the bees themselves. [The other one] is based on an infrared imaging system with a computer program, [in which] we ‘tattoo’ individual bees with tags or barcodes in order to tell them apart. The imaging system can be also used for tracking the bees inside their hives. We can analyze the interaction—for example, trophallaxis—between different bee individuals before and after experimental treatment.”

Without much manual labor, Yang and his team were able to study whether or not forager bees are returning to the hive and monitor the interactions within. The results led them to speculate that imidacloprid may have sublethal effects that propagate homing failure.

The next step after tracking the forager bees was to determine what causes this phenomenon, and it all starts with the honey bee larvae.

Yang and his team fed honey bee larvae different sublethal dosages of imidacloprid and allowed all treatment groups to develop into adults. The adult bee brains were then removed and scanned using a confocal microscopy technique for imaging and further analysis.

Brain imaging revealed that the density of synaptic units in the regions of the calyces was lower among bees treated with imidacloprid compared to an untreated control group. Calyces in a bee’s brain are responsible for the olfactory system and visual functions, which are both essential when foraging. The changes in the bee’s brain suggest that the pesticide damages a young bee’s nervous system and neural connectivity. With an impaired brain, a bee will have reduced olfactory learning abilities. Even though the larvae survives to adulthood, a low dosage of imidacloprid could jeopardize the health of an entire colony.

Yang hopes to continue his interdisciplinary approach on the sublethal effects of pesticides.

“With the aid of my colleagues with engineering backgrounds, I am trying to construct a system to assess the condition of honey bee colonies. I hope our system [will be able to] predict the future of honey bees before they die out.”

Yang encourages the public to learn more about pesticides. He realizes that we cannot completely abstain from using them, but we must know how to use them responsibly.

“Honey bees are suffering.” Says Professor Yang when asked about the current status of honey bees. “Know bees, know lives; no bees, no lives!”

Read more:

• “Impaired olfactory associative behavior of honeybee workers due to contamination of imidacloprid in the larval stage” PLoS One
• “Sublethal Dosage of Imidacloprid Reduces the Microglomerular Density of Honey Bee Mushroom Bodies” Scientific Reports

Constance Lin is a Ph.D. candidate at the Texas A&M University Department of Entomology. She recently graduated from the University of Washington with a B.S. in Environmental Science and Resource Management and is currently a research affiliate at UC San Diego. Email: constance.714@gmail.com