They have found that the infection creates an “energetic stress,” where “the bees are more hungry,” he says. “They try to find food, and beg more for food, making many more contacts with each other than they normally would do. We also find that once they get food, they do not seem to share it with others.”
To track the movement of food, the researchers set up a feeder with sugar syrup containing a marker, sometimes a colored particle or a radioactive tracer. “They eat the food and take it back to the colony, and start passing it to each other,” Naug says. “You can track and see how the food is moving through the colony. This is the way you can model the spread of the disease.”
They also tag the bees with numbers, and video them. “From that, we start to see who interacts with whom,” he says. “We try to build a contact structure inside the colony to see whether we can predict the transmission pattern from that contact structure. And based on our results from the odor experiments, we try to determine why A interacts with B and not with C. What are the underlying mechanisms by which this contract structure is built?”
In another series of experiments, the researchers also found that energetic stress affects cognitive ability and sensitivity to risk. One group of bees made to “learn” an association between two stimuli died four and one-half hours earlier than a control group, suggesting that “when you are energetically low, you do not learn as well, and you are also more risk-prone, trying to meet the energetic demand on you,” Naug says.
“Learning involves spending energy, and it appears that the energetic spending you do can kill you faster, especially when you don’t have a lot of energy to begin with due to an infection,” he adds.
While Naug does not study Colony Collapse Disorder directly, he wonders whether the behavior associated with energetic stress is related.
“Energetic stress could also affect navigational learning,” he says. “When you have a disease, you will be energetically stressed, and the impaired learning might make it more difficult to find your way back home.”