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Researchers log critical breakthrough in the fight against spruce bark beetles

For the first time, an international research team led by Lund University in Sweden has mapped out exactly what happens when spruce bark beetles use their sense of smell to find distressed spruce trees and partners to reproduce with. The hope is that the results will lead to better pest control and protection of European forests in the future.

For the first time, an international research team led by Lund University in Sweden has mapped out exactly what happens when spruce bark beetles use their sense of smell to find distressed spruce trees and partners to reproduce with. The hope is that the results will lead to better pest control and protection of European forests in the future (photo courtesy Erling Jirle).

The Eurasian spruce bark beetle (Ips typographus) is an economically significant forest pest in Europe. Spruce bark beetle outbreaks are common in Norway spruce (Picea abies) forests following storm damage.

The spruce bark beetle population can increase rapidly after a storm event, as newly downed and stressed trees provide suitable breeding conditions. In high population densities scenarios, it can overcome the defense system of healthy spruce trees causing widespread beetle kill.

Furthermore, outbreaks may become a more severe problem in the future, as a warmer climate will increase the likelihood of an additional generation in the annual cycle.

Have matched receptors with pheromones

The spruce bark beetle uses its sense of smell to locate distressed trees and partners. The odours are captured via odorant receptors (proteins) in their antennae. Researchers have long understood the connection, but so far they have not known exactly which receptors bind to what pheromones.

This is key knowledge for the long-term development of more effective and environmentally friendly pesticides and bark beetle traps used to protect the forest from succumbing to widespread infestation.

A spruce forest harvest site in southcentral Sweden. According to the Swedish Forest Agency, in 2019 spruce bark beetles had damaged almost 7 million m3 of wood in the south and central Sweden increasing the cost of harvesting.

The research team was able to characterize the response of odorant receptors in bark beetles for the first time. They identified 73 different receptors in the antennae of the Eurasian spruce bark beetle and succeeded in characterizing the odour response in two of the receptors. One responds to the pheromone ipsenol, the other to ipsdienol.

A large number of different bark beetle species use these pheromones when communicating with scents, so the fact that we have been able to characterize them is a breakthrough, said Martin N. Andersson who led the research group consisting of researchers in Sweden, Germany, and the Czech Republic.

The two receptors are thus the first ever to be characterized in bark beetles. To put the result into context, Andersson says that within the entire insect order Coleoptera beetles, with more than 300 000 species on Earth, only three odour receptors had been characterized previously.

Our results indicate that the pheromone receptors of different beetle species are evolutionarily unrelated, at least in the few species that have been studied. We also show that the odour response in these receptors is very specific, and we are the first in the world to be able to show exactly where in the receptors the pheromones are likely to bind, explained Martin N. Andersson.

The findings have been published in a paper titled “Putative ligand binding sites of two functionally characterized bark beetle odorant receptors” in the journal BMC Biology.

Opens for multi-approach pest control research

The results could make it possible to develop better and more environmentally friendly pest control methods. One approach is to try to find other odours that bind even better to the two receptors than ipsenol and ipsdienol.

If such odours can be found, they can hopefully be used to disrupt the pheromone communication of spruce bark beetles – either by a stronger activation of the receptor compared with the natural pheromone or by blocking the receptor.

Another way could be to use the two characterized receptors in a biosensor that is under development. This would quickly locate spruce bark beetles and thus be able to identify infested trees before the bark beetles spread.

According to Martin N. Andersson, the practical applications are a few years away.

Screening for better substances can begin in 2021. If we find something, the results must be confirmed in the lab and then evaluated in the field, and that would take two or three years. Using it in biosensors for monitoring and detection will probably take longer than that. However, our discovery means that the process can now begin, ended Martin N. Andersson.

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