The study shows that exposure to pesticides can dramatically affect the social behavior of bees

Bumblebee (Bombus impatiens) working in the country, equipped with a unique tracking tag (BEEtag). Credit: James Crall

For bees, it's all social.

Whether it's food, caring for young people, using their bodies to produce heat or for nesting fans or for building and repairing nests, the bee colony makes almost everything as a single unit.

While recent studies suggest that exposure to pesticides could have an impact on dietary behavior, a new study led by James Crall has shown that these effects can only be the tip of the iceberg.

Postdoctoral worker working in Benjamin de Bivort, Professor of Organism and Evolutionary Biology, Thomas D. Cabot, is the lead author of a study showing exposure to neonicotinoid pesticides – the most widely used pesticide group in agriculture – having a profound effect on a number of social behaviors.

Using an innovative robotic bee tracking platform, Crall and co-authors, including de Bivort and Naomi Pierce, biology professor Sidney A. and John H. Hessel, showed that after exposure to pesticides, bees spent less time curing larvae and were less social than other bees. Other tests have shown that the bee's ability to endanger the nest and expose the insulating wax closures around the colony has impaired bee exposure. The study is described in the document of 9 Science.

In addition to the studies of Crall, de Bivort and Pierce, the study was co-authored by Callin Switzer, Ph.D. "18, Stacey Combes of UC Davis, former researchers for the research of the organism and evolutionary biology Robert L. Oppenheimer and Mackay Eyster and Harvard Undergraduate Andrea Brown, 19.

"These pesticides first appeared in the mid-1990s and are now the most commonly used class of insecticides worldwide," Crall said. "They usually work through seed treatment – high concentration is divided into seeds, and one of the reasons why farmers and pesticide companies like these compounds are that they are systematically captured by plants … so it is thought to provide the whole plant resistance. the problem is that they also appear in pollen and nectar bees feed on. "

Over the past decade, Crall has launched a number of studies that linked exposure to pesticides with food cuts, "but there were reasons to suspect it was not the whole picture."

"Forcing is only part of what bumblebees do," Crall said. "These studies have picked out the important implications of these compounds for what's going on outside the nest, but there's a whole world of really important behaviors that's going on inside … and that's the black box we wanted to open a little."

Automated tracking of nesting staff in the bumblebee colony (Bombus impatiens). Credit: James Crall

To make this possible, Crall and his colleagues developed a unique permanent system that allowed them to track the activity of up to ten colonies at one time.

"What we do is put the black and white mark with the simplified QR code on the back of each bee," he said. "And there's a camera that can move around the colony and track the behavior of each bee automatically by computer vision … so it allows us to look into the nest."

In using the system, Crall and colleagues were able to dispense specific individual bees with pesticides and observe changes in behavior-free interactions with nests and spend more time on the periphery of the colony, but these experiments are limited in several important ways.

"One is physiological," Crall said. "Although we give bees realistic pesticide doses, they will drink daily coffee in five minutes than if they were during the day, so giving one big dose may not be absolutely realistic, but another important thing is that the bee colony is a functional unit. individual, because what you lose when you do it is the natural social structure of the colony. "

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

Each of the 12 units of the system, says Crall, contains one colony where bees have access to two chambers – one to mimic the nest and the other to act as nesting space.

"This allows us to perform multiple colony-level exposures and perform continuous monitoring," Crall said. "We think it's much closer to how their natural behavior works, while allowing us to automate tracking behavior across multiple colonies at a time."

As in previous studies, Crall said, exposed bees showed changes in levels of activity and socialization and spent more time at the edge of the nest, but tests also showed that the results were strongest overnight.

"Bees have a very strong circadian rhythm," Crall said. "So what we found was that there was no statistically noticeable effect during the day, but we saw it collapse during the night. We do not yet know whether (pesticides) interfere with the regulation of the circadian gene or whether it is just some, perhaps physiological feedback … but it suggests that, from the practical point of view, if we want to understand or study these compounds, it depends on the effects overnight. "

Manual administration of bumblebee worker (Bombus impatiens) during acute exposure studies. Credit: James Crall

Additional experiments, in which temperature probes were placed inside outdoor bees, suggest that pesticides have a significant effect on bee's ability to regulate temperatures within the nest.

"When the temperatures fall, the bees occupy the wings and tremble in their muscles to create heat," Crall said. "But what we found was that in the control colonies, even though the temperature changed widely, they managed to keep the temperature in the colony stable to several degrees, but exposed bees dramatically lose the ability to regulate the temperature."

In addition to dispersing bees' ability to directly heat or cool the nest, the experiment also showed that exposure to pesticides affected bee's ability to produce an isolation wax seal over a colony.

"Almost all of our control colonies have built this cap," Crall said. "And they seem to be completely destroyed in a colony exposed to pesticides, so they lose that ability to perform this functional restructuring of the nest."

If you go ahead, Crall said, there are other questions the study has raised that he hopes.

"This work – particularly in the field of thermoregulation – opens up a new set of questions not only about the direct effects of pesticides but how these pesticides exacerbate colony's ability to cope with other stressors," he said. "This work suggests that under extremely extreme conditions we could expect that the effects of pesticides will be worse, so it will change how practically we test agrochemicals in general, but points out the specific questions of whether we might see stronger in certain environments."

Overall, Crall believes that the findings point to the need for stricter regulation of neonicotinoids and other pesticides that may affect bees.

"I think we are in a place where we should be very, very concerned about how the ways in which we change the environment are undermining and decimating insect populations that are important not only for the function of each ecosystem … but which are for food production very important, "he said. "Our food system is becoming more and more dependent on pollination over time – today, about a third of crops are dependent on fodder plants and it's just rising. Until now, we had this abundant, natural gift of pollinators working for us, and now we start to realize that it's not given , so I think we should be very afraid of that. "

Explore the following:
The neonicotinoid pesticide affects cultivation and social interaction in bumblebees

More information:
J. D. Crall et al., & Quot; Neonicotinoid exposure disrupts the behavior of nesting bumblebee, social network and thermoregulation & quot; Science (2018). … 1126 / science.aat1598

"Pesticides affect the social behavior of bees," Science (2018). … 1126 / science.aav5273

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