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Tick-free forest playground

Rampaging around on a forest playground, sweating on a keep-fit track, grilling sausages in a BBQ area – these innocent activities always have an element of danger involved – namely the fear of ticks. To try and free us from this danger, researchers at the University of Hohenheim are developing biological methods to eradicate ticks.

Tick bites can have dangerous consequences as ticks carry a broad range of different pathogens. According to information from the German Borreliosis and TBE Association, in Germany every year 240,000 people contract Lyme disease and 300 TBE (tick-borne encephalitis). Now there is hope for parents, sportspeople and BBQ lovers to come closer to a tick-free recreation area. It is hoped that the release of specific tick predators will help eradicate ticks from certain areas. Biologists at the University of Hohenheim have spent three years searching for, and testing, the best tick eaters. The results are part of the “Borreliosis Prevention” research project that was commissioned by the Landesstiftung Baden-Württemberg foundation.
Experimental fungus attacking a tick – scanning electron microscope image (Photo: University of Hohenheim)
The tick’s extremities are stunted, the carapace overgrown with a cotton-wool like fleece and transparent threads are protruding from the joints. Prof. Dr. Ute Mackenstedt likes such pictures: “These fungi form aesthetically beautiful growths.”

The microscope image shows a dead tick. The fleece on its carapace is the result of the action of one of the most promising experimental fungi. Within one month, the fungus spreads within the tick. In the “Borreliosis Prevention” project, the Hohenheim researchers have identified some very efficient fungi that led to a mortality rate of up to 85% (depending on the developmental stage) among ticks within about a month of exposure of the ticks to the fungi.

Fighting ticks with fungi and similar organisms has a decisive advantage. All these organisms are natural tick enemies that are endemic to Germany. They are cultured in the laboratory and released in recreation areas and are able to eradicate ticks more efficiently than the use of chemicals.

Increasing resistance to chemicals

Prof. Dr. Ute Mackenstedt coordinates the Borreliosis Prevention project at the University of Hohenheim. (Photo: University of Hohenheim)
“African cattle breeders have extensive experience in combating ticks with chemicals,” said Prof. Dr. Mackenstedt explaining that the cattle in Africa are regularly driven through toxin troughs. However, this is no appropriate method for getting rid of ticks on forest playgrounds. Moreover, the parasites are becoming increasingly resistant to the chemicals used.

The Hohenheim researchers resorted to a broad range of natural tick enemies, but excluded exotic organisms right from the beginning: “The effects on the domestic ecosystem would have been incalculable.”

In order to make sure that the candidate organism inhabited the same area as the ticks, the researchers combed through Stuttgart bushes and meadows looking for sick ticks. They isolated fungi and roundworms from sick tick bodies and provided them with ideal culture conditions in the laboratory incubators. Whilst concentrating on fungi and other parasites, the researchers in the neighbouring building under Prof. Dr. Johannes Steidle tried to do the same thing with tiny ichneumon flies.

The practical test was undertaken in small steps: “At the beginning we brought the predators and the ticks together in sterile glass dishes, later on they were exposed to each other under more natural conditions in a terrarium,” said Prof. Dr. Mackenstedt.

Fungi against young ticks, roundworms against adult bloodsuckers

The fungi turned out to be particularly promising tick predators. “In practice, we can also combine the fungi with other tick enemies,” explained the parasitologist in a reference to the ticks’ complex biology with multi-year developmental stages. “Our fungi and mini-wasps are very effective against nymph-stage ticks. Roundworms are best for killing adult ticks.”

With their research into biological tick control, the researchers are covering new ground, not only because of the complex biology of the tick but also because of the complex relationships between the various organisims involved. “The combination of two organisms in their natural environment such that one of the two destroys the other is a highly complex process,” said Prof. Dr. Mackenstedt. “We also have to take great care not to damage other species.”

Following promising laboratory investigations, the biologists now have plans to investigate fungi, worms and other organisms in the field. “The first phase of this investigation was made possible through the Landesstiftung Baden-Württemberg foundation. We now hope to find further funding that will enable us to take the concept to application.”

Website address: https://www.biooekonomie-bw.de/en/articles/pm/tick-free-forest-playground