Research   Theses  CV  Publications  Presentations  Awards  help    to staff list 

"As soon as we study animals - not in laboratories and museums only, but in the forest and the prairie, in the steppe and the mountains - we at once perceive that though there is an immense amount of warfare and extermination..., there is, at the same time, as much, or perhaps even more, of mutual support, mutual aid, and mutual defence..." Kropotkin 1902

A major focus of our research is on multitrophic interactions between insects, fungi, and bacteria. Our main model systems are the fungus-farming ambrosia beetles (Curcullionidae: Scolytinae and Platypodinae). These beetles live in a close symbiosis with fungi, which they actively cultivate within their nests in the hardwood of trees. While the beetles depend on their fungal crops for feeding, the fungi depend on the beetles for dispersal to new habitats. Third players in this interaction are microbes. As recent studies indicate, the beetles apply these microbes to their fungus gardens. The microbes produce antibiotics, thereby likely helping the beetles to fight weeds in their gardens. The detailed mechanisms of fungus farming in ambrosia beetles, however, still await discovery. We study these mechanisms using a broad array of methods from micro- and molecular biology.
The evolution of fungus-farming is closely associated with the evolution of sociality. Fungus-farming insects usually live in family groups and divide labor within their nests. In ambrosia beetles, the tasks range from weeding the fungus gardens to enlarging the nest and protecting it against intruders. Even the larvae take over specific tasks, a behavior that is not known for any other holometabolous insects. Unlike it is the case in other social insects, ambrosia beetle workers are not sterile, but keep their ability to reproduce. Nevertheless, they decide to stay within their natal nest and help with fungus-farming, at least for a certain period. Ambrosia beetles are therefore excellent model systems to study the evolutionary mechanisms that select for a social lifestyle. This is another focus of our research.

Specific projects

(1) Farming in beetles: Microbial symbionts and their functions in fungus-culturing beetles
Ambrosia beetles live within self-dwelled systems in wood. On the walls of the tunnels and chambers, they grow their fungal gardens. In this project, we aim at gaining insights into the mechanisms of beetle fungiculture.
The gardens are dominated by one food-fungus, but other microbes grow there as well. Some mold fungi seem to be parasitic, and they negatively affect offspring numbers of the beetles. In a first step we identify the community of microbes associated with two native ambrosia beetle species, Xyleborinus saxesenii and Xylosandrus germanus. We also investigate the succession in which different microbes occur within the nests. Subsequently, we test how these microbes interact with each other. To this end, we apply state-of-the-art molecular and visualizing techniques (i.e., next-generation sequencing, SEM, FISH).
Previous studies have indicated that X. saxesenii beetles are able to influence the fungi growing in their nests in two ways: First, they are able to suppress the spread of molds. Second, they can enhance the growth and fruiting of their food-fungus. The underlying mechanisms of these effects are also studied in this project.
Elucidating the methods that the beetles apply might also awaken us for novel approaches in human agriculture. After all, insect farmers have evolved evolutionary stable mechanisms of sustainable fungiculture. These mechanisms have obviously allowed them to defend their crops against pathogens over millions of years, and, most importantly, to avoid the evolution of resistances in their crop pests.
Preliminary results indicate that the beetles make use of antibiotic-producing bacteria, which hence represent a third mutualistic player in this system.

People involved in this project
Pamela Baumann (Bachelor thesis)

Dan Vanderpool, Microbial genomics and symbiosis, Univ. of Montana, US
Dr. Miroslav Kolarik, Institute of Microbiology, Czech Academy of Science, Prague, CZ

Further reading
Popular science article:

(2) Bacterial and fungal symbionts of parasitic Dendroctonus bark beetles
Bark beetles (Curculionidae: Scolytinae) of the genus Dendroctonus are widely used as model insects to study symbiosis, due to their diverse ecologies and economic impacts. Little research has been done on parasitic Dendroctonus species which develop on living, trees, which are continuously defending themselves. Dendronoctus species are therefore hypothesized to associate with peculiar bacterial and fungal microorganisms. In this study, using complimentary culture-dependent and culture-independent methods, we provide the first comprehensive overview of the bacterial and fungal symbionts of the parasitic beetles D. micans, D. punctatus, and D. valens, and we compare their microbial communities with those of other tree-inhabiting insects. Many bacteria and yeasts are shared throughout the three species and their developmental stages, especially nitrogen-fixing and detoxifying microorganisms. Our study casts new light on the symbionts of bark beetles, and will contribute to understand how symbioses affect insects with various ecologies.

People involved in this project
PhD project of Loic Dohet, Université Libre de Bruxelles, Brussels, Biological Control and Spatial Ecology Lab (LUBIES), BE

(3) Social immunity in ambrosia beetles & chemical recognition of fungal symbionts
In complex insect societies, the different individuals live in close spatial association and are highly related to each other. This should favor the evolution of social behaviors to fight threats imposed by parasitic microbes, besides the chemical defense mechanisms.
We study these mechanisms in the ambrosia beetle Xyleborinus saxesenii. First results show that the beetles actively up-regulate hygienic behaviours like allo-grooming, self-grooming and cannibalism, when they are experimentally exposed to pathogenic micro-organisms. Such social immune responses were not known in beetles before.
We found an attraction of the beetles to the volatiles of their main mutualistic fungus and to ethanol which indicates that the beetles select new breeding grounds by the based on the presence of con-specifics that already founded a fungus garden successfully survival probability of their associated ambrosia fungus and the status of the host tree. But we did not find a repellent effect of volatiles produced by pathogenic fungi on the beetles during dispersal.

People involved in this project
MSc and PhD project of Jon Andrea Nuotclà, Behavioural Ecology Group, University of Bern, CH

Dr. Gerrit Holighaus, Dep. Forest Zoology, University of Göttingen, DE
Dineshkumar Kandasamy, Dep. Biochemistry, MPI-CE, DE

...more projects coming soon!
last updated on 2016-04-09