It is not only the Thuringian Forest that is once again being ravaged by a major bark beetle infestation this year, causing many spruce trees to die and ultimately likely altering the entire forest ecosystem in the future. This is primarily due to drought—a consequence of global warming—and the lack of diversity in most of our native forests. However, we also repeatedly find that there are still quite a few unanswered scientific questions regarding the fundamentals and core issues of bark beetle infestations—such as exactly which trees are infested and why.
In our department, we are striving to find answers to precisely these questions. For example, we are investigating the exact mechanisms from the tree’s perspective. We are interested in why, despite mass reproduction of the bark beetle (European spruce bark beetle, Ips typographus), some spruce trees (Picea abies) in the forest are preferentially infested while others are not infested at all. To do this, we create genetically modified trees and alter the composition of the tree resin—which is the spruce’s primary defense mechanism—as well as the scent that plays a crucial role in helping the bark beetle locate attractive trees. We then test in the laboratory how the beetles react to these changes.
At the same time, however, we are also trying to gain new insights into the bark beetle. This is because the beetle does not live alone but in symbiosis with a multitude of microorganisms. For example, its body surface hosts a variety of fungi that likely play an important role in the digestion of its food. In addition, the beetle’s gut contains a complex mix of specialized bacteria that primarily break down the tree’s toxic defense compounds, thereby making the food more digestible for the beetle. To confirm these hypotheses and ultimately gain a better understanding of this complex system, we are attempting to identify the chemical substances involved and are also conducting tests in our laboratories on the behavior of European spruce bark beetles in the presence of both fungi and bacteria. To gain further insights into this symbiotic beetle-fungus-bacteria system, we are also using the slightly larger and easier-to-keep spruce weevil (Hylobius abietis). Although this beetle feeds only on the bark of young trees, it is likely to harbor a comparable community of fungi and bacteria, since it is confronted with the same constituents and defense compounds in the tree as the European spruce bark beetle.
At our booth, we will present the latest research findings, the organisms under study—such as transgenic spruce trees, European spruce bark beetles, and spruce weevils, as well as their associated fungi and bacteria—and some of the experimental setups used for laboratory testing.
