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


Bumblebee worker (Bombus impatiens), located in the open, equipped with unique tracking marks (BEEtag). Credit: James Crall

For bees, it's all social.

Whether it is for food for food, for the care of young people, using their bodies to generate heat or to empty the nest, or build and repair the nest, the bee colony makes everything around itself as a unique unit.

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

Post-doctoral associate who works in the laboratory Benjamin de Bivort, Thomas D. Cabot is an associate professor of organizational and evolutionary biology, Crall is the lead author of a study that shows exposure to neonicotinoid pesticides – the most commonly used pesticide class in agriculture – has profound effects on a multitude of social behaviors.

Using an innovative robotic platform to observe bee behavior, Crall and co-authors, including de Bivort and Naomi Pierce, biology professor Sidney A. and John H. Hessel showed that after pesticides, bees spend less time to care for larvae and were less social than other bees. Additional tests have shown that the beehive release capability is able to warm the nest and build insulating wax caps around the colony. The study was described in a document dated November 9 in Science.

In addition to Crall, de Bivort and Pierce, the study was co-authored by Dr. Callin Svitzer, Ph.D. & # 39; Stacey Combes, UC Davis, former associates for organism and evolutionary biology Robert L. Oppenheimer and Mackai Eister and Harvard Undergraduate Andrea Braun, 19.

"These pesticides were first put into use in the mid-1990s and are now the most commonly used species of insecticides around the world," said Crall. "Usually they work through seed treatment – high concentrations are applied to seed, and one reason why farmers and pesticide companies, such as these compounds, are systematically taken into operation … so the idea gives total resistance but the problem is that they appear on the pollen and nectar bees are fed. "

Over the past decade, Crall said, numerous studies have linked exposure to pesticides with food disorders, "but there are reasons to doubt that this is not the whole picture."

"Foraging is just a part of those bumblebees who work," Crall said. "These studies have picked up the important effects these compounds had on what is happening outside the nest, but there is a whole world of really important behaviors inside … and that's the black box we wanted to open a little."

Automatic monitoring of nursery workers in the bumblebee colony (Bombus impatiens). Credit: James Crall

To do this, Crall and colleagues developed a unique benchtop system that enabled them to make bee activities in as many as a dozen colonies.

"What we do is put a black and white label with a simplified KR code on the back of each bee," he said. "And there is a camera that can move across colonies and automatically monitor the behavior of each bee using computer vision … so it allows us to look inside the nest."

Using the system, Crall and colleagues managed to breed specific, single bees with pesticide and observed changes in their behavior of minor interaction with disappearance and spend more time on the periphery of the colony – but these experiments were limited in several important ways.

"One is physiologically," Crall said. "Although we have given real bee pesticide bees, drinking a cup of coffee in five minutes will be different from the spread over the day, so giving a single dose may not be completely realistic, and the other important thing is that a colony of bees is a functional unit. What you lose when you do it is the natural social structure of the colony. "

With the robotic system, however, researchers can treat the whole colony as a single unit.

Each of the 12 units of the system, Crall said, has a unique colony in which bees have access to two chambers – one to imitate the nest, and the other to act as a place for food.

"This allows us to do multiple colonial exposure and to conduct continuous monitoring," said Crall. "We think this is much closer to the way in which their natural behavior works, and it also allows us to automate tracking behavior across multiple colonies at the same time."

As was the case in earlier studies, Crall said, the exposed bees showed changes in activity levels and socialization, and spent more time on the edges of the nest, but the tests also showed that the results were the strongest overnight.

"The bees really have a strong circadian rhythm," explained Crall. "What we found was that during the day there was no statistically significant effect, but at night we could see that it was breaking down. We still do not know if (pesticides) disturb the circadian regulation of the gene, or if this is just some, perhaps physiological feedback. but it suggests that, from a practical perspective, if we want to understand or study these compounds, looking at effects overnight, it is very important. "

Manual feeding of bumblebee workers (Bombus impatiens) during acute exposure examinations. Credit: James Crall

Additional experiments in which temperature probes are placed inside open hives, the proposed pesticides have profound effects on the ability of bees to regulate temperatures inside the nest.

"When the temperature drops, the bees have wrenched their wings and shaken their muscles to produce heat," said Crall. "But what we found was that, in control colonies, even when the fluctuations in temperature fluctuated widely, they could keep the temperature in the colony stable at several degrees. But exposed bees, they dramatically lose the temperature regulating capacity."

In addition to the disturbance of the bees' ability to directly warm or cool the nest, the experiment also showed that exposure to pesticides affected the beehive's ability to build an insulating wax cap over the colony.

"Almost all our control colonies built that cap," said Crall. "It seems to have been completely destroyed in colonies exposed to pesticides, so they lose this capacity to perform this functional restructuring of the nest".

Progressing, Crall said, there are still some additional questions from the study that he hopes will address.

"This work – especially on thermoregulation – opens up a new set of questions, not just about the direct effects of pesticides, but how these pesticides make it difficult for colonies to deal with other stressors," he said. "This paper suggests that in particularly extreme environments, we can expect that the effects of pesticides are worse, so it changes how we practically test agrochemicals in general, but points to specific questions about whether we can see stronger declines in certain environments."

Taken together, Crall believes that the finding points to the need for more rigorous regulation of neonicotinoids and other pesticides that can affect bees.

"I think that we are at that point where we should be very, very concerned about the way in which we change our environment, raising and destroying insect populations that are important not only for the function of each ecosystem … but which are very important for food production, "he said. "Our food system is becoming more and more pollinators, depending on the time – today about a third of food crops depend on pollinators, and this only increases. So far, we have had this rich, natural gift of pollinators who do this all we do for us, and now we're starting to realize that it's not given, so I think we should take care of it. "

Explore further:
Neonicotinoid pesticide affects food and social interaction in bumblebee

More information:
J.D. Crall el al., "Exposing neonicotinoids impedes the behavior of bumblebee nests, social networks and thermoregulation", Science (2018). / cgi / doi … 1126 / science.aat1598

"Pesticide affects the social behavior of bees" Science (2018). / cgi / doi … 1126 / science.aav5273

Reference of the journal:

Harvard University

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