Study shows pesticide exposure can have a huge impact on bees' social behavior

For bees, being social is everything.

Whether it's looking for food, caring for young people, using their bodies to generate heat or to cool the nest, or to build and repair nests, a colony of Bees does pretty much everything in one unit.

Although recent studies suggest that pesticide exposure may affect foraging behavior, a new study, led by James Crall, has shown that these effects may be just the top of the story. 'iceberg.

Postdoctoral researcher working in Benjamin Bivort's laboratory, associate professor of biology of organisms and evolution Thomas D. Cabot, Crall is the principal author of a study showing exposure to Neonicotinoid pesticides, the most used class of pesticides in agriculture – has profound effects on a host of social behaviors.

Using an innovative robotic platform to observe bee behavior, Crall and his co-authors, including Bivort and Naomi Pierce, professor of biology at Sidney A. and John H. Hessel Universities, have shown that, following Pesticide exposure, bees spent less time in nursing. larvae and were less social than other bees. Additional tests showed that the exposure reduced the ability of bees to warm the nest and build insulating wax capsules around the colony. The study is described in a 9 November article in Science.

In addition to Crall, Bivort and Pierce, the study was co-authored by Callin Switzer, Ph.D. 18, Stacey Combes of UC Davis, former research assistants in organismic and evolutionary biology, Robert L. Oppenheimer and Mackay Eyster and Harvard undergraduate student, Andrea Brown, 19th.

"These pesticides were used for the first time in the mid-1990s and are now the class of most used insecticides in the world," said Crall. "Generally, they work through seed treatment – high concentrations are dosed on the seeds, and one of the reasons that farmers and pesticide manufacturers like these compounds is that they are so absorbed." systemic by plants … so the idea is that they offer resistance to the whole plant.But the problem is that they also appear in pollen and that bees feed on nectar. "

According to Dr. Crall, over the past decade, several studies have linked pesticide exposure to foraging disturbances, "but there was reason to believe that this is not the case. was not everything. "

"Foraging is only one part of what bumblebees do," Crall said. "These studies showed the important effects of these compounds on what was happening outside the nest, but there is a whole world of very important behaviors inside … and it's a black box that we wanted to open a little. "

To do this, Crall and his colleagues have developed a unique system, which allows them to track the activity of bees in a dozen colonies at a time.

"What we do is put a black and white label with a simplified QR code on the back of each bee," he said. "And there is a camera that can move over the settlements and track the behavior of each bee automatically with the help of computer vision … so we can look inward of the nest. "

With the help of the system, Crall and his colleagues were able to dose the pesticide to certain bees and observe the behavior changes of these – less interaction with nest mates and longer time at the periphery colony – but these experiments are limited in many cases. important means.

"One is physiological," Crall said. "Even if we give bees realistic doses of pesticide, drinking your daily coffee in five minutes will be different from spreading it during the day, so giving a large dose may not be realistic. Another important element is that a colony of bees is a functional unit.This does not make sense to treat individuals because what you lose by doing it is the structure natural social life of the colony. "

With the robotic system, however, researchers can treat an entire colony as one unit.

According to Crall, each of the 12 units of the system houses a single colony where bees have access to two chambers: one to mimic the nest and the other to serve as a feeding place.

"This allows us to do multiple exposure at the colony level and to do ongoing surveillance," said Crall. "We think this is much closer to the way their natural behavior works, and it also allows us to automate behavioral tracking across multiple colonies at the same time."

Just as in previous studies, exposed bees show changes in activity and socialization levels and spend more time at the nest margin, but tests also showed that results were strong overnight.

"The bees actually have a very strong circadian rhythm," Crall explained. "So we found that during the day there was no effect statistically observable, but at night we could see that they were collapsing." We do not yet know if (pesticides ) disrupt the regulation of circadian genes or if it's just a little, maybe a physiological return … but that suggests that, from a practical point of view, if we want to understand or study these compounds, it is very important to 'examine the effects overnight.'

Additional experiments, in which temperature probes were placed in outer hives, suggested that pesticides have profound effects on the ability of bees to regulate temperatures within the nest.

"When temperatures drop, bees sink their wings and shiver to generate heat," Crall said. "But what we found was that in the control colonies, even though the temperature fluctuated considerably, they were able to maintain the temperature in the colony to within a few degrees, but the exposed bees lost their capacity considerably. temperature control. "

In addition to disrupting the ability of bees to directly heat or cool the nest, the experiment also revealed that pesticide exposure affected the ability of bees to build an insulating wax cap on the colony.

"Almost all of our control colonies have built this cap," said Crall. "And it seems to be totally wiped out in colonies exposed to pesticides, so that they're losing their ability to perform this functional restructuring of the nest."

Crall added that the study he hoped to address raises additional questions.

"This work, particularly on thermoregulation, raises new questions not only about the direct effects of pesticides, but also about how these pesticides prevent colonies from coping with other stressors," he said. declared. "This work suggests that in particularly extreme environments we might expect perverse effects from pesticides, so it changes the way we carry out practical trials of agricultural chemicals in general, but it raises specific questions about to know if we could see stronger decline in some environments. "

Overall, Crall thinks that the results underscore the need for tighter regulation of neonicotinoids and other pesticides that may impact bees.

"I think we are at a point where we should be very, very concerned about how we are changing the environment, which is undermining and decimating insect populations that are important not just for the functioning of each and every one of us. ecosystem … but are very important for food production, "he said. "Our food system is increasingly dependent on pollinators, and today about one-third of food crops are pollinator-dependent, and that's only going up." Natural and abundant pollinator donation work for us, and now we are starting to realize that this is not a given, so I think we should be very worried about it. "

Explore further:
Neonicotinoid pesticides affect foraging and social interactions in bumblebees

More information:
J.D. Crall el al., "Exposure to neonicotinoids disrupts drone nest behavior, social networks and thermoregulation" Science (2018). science.sciencemag.org/cgi/doi… 1126 / science.aat1598

"Pesticides affect the social behavior of bees" Science (2018). science.sciencemag.org/cgi/doi… 1126 / science.aav5273