In the contaminated area around Fukushima, Japan, scientists are studying the impact of radioactivity on the cognitive abilities of pollinating insects such as honeybees and giant hornets.
Bees and hornets are known to have a wide range of cognitive skills, including the ability to recognise colours and navigate in space. However, pollution by substances released into the environment by humans, such as pesticides, can impair their performance.
Olivier Armant, from the radionuclide ecology and ecotoxicology laboratory at the French ASNR nuclear safety and radiation protection authority, and Mathieu Lihoreau, an ethologist from the Research Centre on Animal Cognition at the Centre for Integrative Biology wondered what effect ionising radiation might have on these pollinators. Armant works on the ecological impact of such radiation, carrying out long-term studies on the fauna and flora around Chernobyl (currently inaccessible, due to the war in Ukraine) and Fukushima, Japan, while Lihoreau focuses on bee intelligence and the factors that may interfere with it.
Assessing cognitive performance
"A few years ago, a researcher in my lab came up with the idea of deploying various types of sensor to monitor, preferably automatically, the biological activity of certain species in the aftermath of the Fukushima disaster," Armant explains. "We had three projects in mind: connected nest boxes, a system that measured the biotic parameters of water and – the one we chose – the method developed by Mathieu Lihoreau." For several years, the ethologist has been working on an automated system to assess the cognitive performance of these social insects. The device they use was designed in partnership with the Toulouse-based start-up BeeGuard, which manufactures connected beehives that enable real-time monitoring.
"I study the learning and memory abilities of bees," Lihoreau explains. "Although this is primarily a fundamental research topic, it also has very concrete applications in ecotoxicology: if bees exhibit learning deficits in certain locations, it means there's a problem. For example, although many pesticides are used in doses that are low enough not to kill these insects, they end up as residues in the nectar they feed on and can have a neurotoxic effect. This results in cognitive disturbances that are difficult to observe, such as the inability to associate a reward with a specific colour or smell. Our system can measure these effects, which, although not lethal, are nonetheless serious, because they have a knock-on effect on the survival of colonies and, more generally, on pollination services."
When disturbed in this way, bees begin to forage on flowers of different species, instead of focusing on just one. As a result, they no longer bring the right pollen to the right plants, which affects the entire ecosystem. The device developed by Lihoreau's team (made up of biologists, engineers, modellers and ecologists) had until now only been tested near Toulouse (southwestern France), rather than in the extreme conditions of an area like Fukushima, which the scientists were able to enter with the help of their Japanese colleagues.
"We started collaborating with Japan just after the Fukushima disaster, in 2011," Armant explains. "We work in particular with Fukushima University's Institute of Environmental Radioactivity (IER), which help us to access the contaminated area. Our Japanese colleagues have extensive knowledge of the site and its forests, and they were able to direct us to the most interesting locations. This enabled us to carry out two field investigations in 2023 and 2024."
How do you go about testing bees?
The sites where the beehives were set up were selected on the basis of the soil contamination gradient for caesium-137. Local hornets, already present on the sites, were also included in the cognition study. Although it isn't clear whether these species are pollinators, they are worth studying, as they are descended from many generations of insects exposed to radiation.
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