Researchers boost insect aggression by altering brain metabolism

Scientists report they can crank up insect aggression simply by interfering with a basic metabolic pathway in the insect brain. Their study, of fruit flies and honey bees, shows a direct, causal link between brain metabolism (how the brain generates the energy it needs to function) and aggression.

The team reports its findings in the Proceedings of the National Academy of Sciences.

The new research follows up on previous work from the laboratory of University of Illinois entomology professor and Institute for Genomic Biology director Gene Robinson, who also led the new analysis. When he and his colleagues looked at brain gene activity in honey bees after they had faced down an intruder, the team found that some metabolic genes were suppressed. These genes play a key role in the most efficient type of energy generation in cells, a process called oxidative phosphorylation.

“It was a counterintuitive finding because these genes were down-regulated,” Robinson said. “You tend to think of aggression as requiring more energy, not less.”

In the new study, postdoctoral researcher Clare Rittschof used drugs to suppress key steps in oxidative phosphorylation in the bee brains. She saw that aggression increased in the drugged bees in a dose-responsive manner, Robinson said. But the drugs had no effect on chronically stressed bees – they were not able to increase their aggression in response to an intruder.

“Something about chronic stress changed their response to the drug, which is a fascinating finding in and of itself,” Robinson said. “We want to know just how this experience gets under their skin to affect their brain.”

In separate experiments, postdoctoral researcher Hongmei Li-Byarlay and undergraduate student Jonathan Massey found that reduced oxidative phosphorylation in fruit flies also increased aggression. Using advanced fly genetics, the team found this effect only when oxidative phosphorylation was reduced in neurons, but not in neighboring cells known as glia. This finding, too, was surprising, since “glia are metabolically very active, and are the energy storehouses of the brain,” Robinson said.

The findings offer insight into the immediate and longer-term changes that occur in response to threats, Robinson said.

“When an animal faces a threat, it has an immediate aggressive response, within seconds,” Robinson said. But changes in brain metabolism take much longer and cannot account for this immediate response, he said. Such changes likely make individuals more vigilant to subsequent threats.

“This makes good sense in an ecological sense,” Robinson said, “because threats often come in bunches.”

The fact that the researchers observed these effects in two species that diverged 300 million years ago makes the findings even more compelling, Robinson said.

“Because fruit flies and honey bees are separated by 300 million years of evolution, this is a very robust and well-conserved mechanism.”

Pesticide combination affects bees’ ability to learn

Two new studies have highlighted a negative impact on bees’ ability to learn following exposure to a combination of pesticides commonly used in agriculture. The researchers found that the pesticides, used in the research at levels shown to occur in the wild, could interfere with the learning circuits in the bee’s brain. They also found that bees exposed to combined pesticides were slower to learn or completely forgot important associations between floral scent and food rewards.

In the study published today (27 March 2013) in Nature Communications, the University of Dundee’s Dr Christopher Connolly and his team investigated the impact on bees’ brains of two common pesticides: pesticides used on crops called neonicotinoid pesticides, and another type of pesticide, coumaphos, that is used in honeybee hives to kill the Varroa mite, a parasitic mite that attacks the honey bee.

The intact bees’ brains were exposed to pesticides in the lab at levels predicted to occur following exposure in the wild and brain activity was recorded. They found that both types of pesticide target the same area of the bee brain involved in learning, causing a loss of function. If both pesticides were used in combination, the effect was greater.

The study is the first to show that these pesticides have a direct impact on pollinator brain physiology. It was prompted by the work of collaborators Dr Geraldine Wright and Dr Sally Williamson at Newcastle University who found that combinations of these same pesticides affected learning and memory in bees. Their studies established that when bees had been exposed to combinations of these pesticides for 4 days, as many as 30% of honeybees failed to learn or performed poorly in memory tests. Again, the experiments mimicked levels that could be seen in the wild, this time by feeding a sugar solution mixed with appropriate levels of pesticides.

Dr Geraldine Wright said: “Pollinators perform sophisticated behaviours while foraging that require them to learn and remember floral traits associated with food. Disruption in this important function has profound implications for honeybee colony survival, because bees that cannot learn will not be able to find food.”

Together the researchers expressed concerns about the use of pesticides that target the same area of the brain of insects and the potential risk of toxicity to non-target insects. Moreover, they said that exposure to different combinations of pesticides that act at this site may increase this risk.

Dr Christopher Connolly said: “Much discussion of the risks posed by the neonicotinoid insecticides has raised important questions of their suitability for use in our environment. However, little consideration has been given to the miticidal pesticides introduced directly into honeybee hives to protect the bees from the Varroa mite. We find that both have negative impact on honeybee brain function.

"Together, these studies highlight potential dangers to pollinators of continued exposure to pesticides that target the insect nervous system and the importance of identifying combinations of pesticides that could profoundly impact pollinator survival."

Honey bees trained to stick out their tongues for science

Biologists at Bielefeld University have trained honey bees to stick out their tongues when their antennae touch an object.

The tactile conditioning study was conducted by a team from the lab of Volker Dürr, professor for biological cybernetics at Bielefeld, and will allow researchers to investigate how the honey bees use touch in pattern recognition and sense memory.

"We work with honey bees because they are an important model system for behavioural biology and neurobiology," explained Dürr. "They can be trained. If you can train an insect to respond to a certain stimulus, then you can ask the bees questions in the form of ‘Is A like B? If so, stick your tongue out’."

The process by which a bee sticks out its tongue when faced with a stimulus is known as the proboscis extension response. It can be conditioned in the bees as a response to a particular textured surface using sugar water. Each time a harnessed honey bee’s antennae touched the surface, the bee was given sugar water. Eventually the bee extends its tongue whenever it touches the right surface.

Currently the biologists are hoping to use the response to find out more about how bees use antennae movements to gather information about their surroundings.

"It is clear that if a bee touches something with an antenna, a finely textured structure, the bee has to move it to get the information it wants," adds Dürr. "We don’t fully understand the relevance of this movement."