Combating ticks with natural enemies
University of Hohenheim researchers are hoping to receive help from nature in their fight against ticks. Worms, fungi and wasps that feed on ticks will now be used to reduce the number of these dangerous disease carriers.
Ticks like butyric acid which they sense with chemoreceptors located in the insects’ Haller’s organ. People give away their presence by butyric acid, a constituent of human sweat. The bloodsuckers will then grasp the chance to clasp to the wanderer’s limbs or clothing when swept off bushes or blades of grass. The ticks are not dangerous because they suck blood, but because they transfer dangerous pathogens while sucking. Bacterial borreliosis (lyme disease) and viral tick-borne meningoencephalitis (TBE) can also lead to the death of the infected person if left untreated.
TBE vaccines are available to protect humans against meningoencephalitis, but no vaccine is currently available for the treatment of lyme disease. That is why high priority must be given to eradicating ticks. In Germany, efforts to eradicate the insects are focused on the tick Ixodes ricinus which accounts for approximately 95 per cent of the entire German tick population. In a project funded by the Landesstiftung Baden-Württemberg Foundation, scientists led by Prof. Dr. Ute Mackenstedt of the University of Hohenheim are investigating natural ways of combating this tick species. The team includes scientists from the State Health Authorities (LGA) and the departments of parasitology and animal ecology at the University of Hohenheim.
The university and LGA are working closely together
”In Baden-Württemberg, the LGA is the central contact with regard to tick-borne disease,” said Mackenstedt. She is very happy with the excellent cooperation that her team has with the LGA in the tick project that has grown significantly over the years. This has been, to a large extent, due to Dr. Rainer Oehme, who studied at the University of Hohenheim and then did his doctoral thesis on ticks at the LGA. Nowadays, Oehme works in the Department of General Hygiene and Infection Protection in the LGA. ”For few years we worked together on an informal basis, then we finally signed a cooperation agreement and are now working together even more efficiently,” said Oehme.
Steinernema carpocapsae, threadworms which specifically attack well-nourished tick females. (Photos: Department of Parasitology, Institute of Zoology, University of Hohenheim)
The close cooperation of the two researchers led to a grant from the Landesstiftung Baden-Württemberg Foundation to support the project. The three-year project on the eradication of ticks started in March 2005. ”We are bringing fungi and nematodes together with ticks under controlled conditions and observing what happens,” said Mackenstedt explaining that the researchers are specifically focused on the insects’ pathogenicity, demands of the insects on the environment and ecological consequences the release of fungi and nematodes might have. ”It is very important to investigate the potential effects on the ecosystem. Such examinations are also important for receiving authorisation to release the natural tick predators,” said Oehme. ”We are conducting complex laboratory examinations in order to find out whether other arthropods, such as useful soil mites, are also attacked by the tick predators,” added Mackenstedt.
Specificity is essential
“There are many species of fungi which are all different in their virulence against ticks,” said Mackenstedt. She and her colleagues have tested numerous fungal isolates which they came across while studying the current scientific literature. They have excluded non-endemic species from their examinations. ”There are numerous fungi that are used in the tropics for the control of pests.”
Ticks are brought together with their predators in microcosms under controlled conditions. The heated filaments around the battery prevent the ticks from climbing over the rims.
We are strictly against using such exotic insects in our studies because we want to prevent potential negative effects of releasing exotic species into our ecosystem,” said Mackenstedt who, together with her team, has frequently been out to collect new isolates from the environment. They have also collected ticks in the Stuttgart area and cultivated insects that were affected by fungi.
”We have come across a fungi, a metarhizium species, that is particularly aggressive towards ticks,” said Mackenstedt explaining that the effect always also depends on the life stage of the ticks. In general, fungi are most effective against tick larvae and, though slightly less, against nymph-stage ticks. Nematodes (threadworms) are mainly effective against adult ticks, and in particular females that have just enjoyed a blood meal. Mackenstedt’s team is also investigating the worm Steinernema carpocapsae, which is already successfully used for the control of pests in tomato and other monocultures.
Since Steinernema is already established, it might be relatively easy to get approval from the authorities. This would certainly make the worm a good candidate for the researchers’ tick eradication project. It is however assumed that it is not the worm itself that kills the ticks. ”Nematodes contain Xenorhabdus bacteria. We assume that it is these bacteria that affect the ticks,” said Mackenstedt whose team has established a bacterial culture in order to examine whether the bacteria are able to kill the ticks in the absence of the nematodes.
The threads of the fungi Metarhizium anisopliae cover the body of a tick.
Maximal fighting power in combination
Mackenstedt is currently working to combine fungi and threadworms in order to achieve the best efficiency possible. ”We are hoping to combine the antagonists in an environment that suits both of them. Fortunately, both of them require a relatively high degree of humidity.” The first tests have been carried out in Petri dishes and are now being tested in microcosmic conditions, i.e. larger plastic dishes with clearly defined substrates and climate, in which the ticks are brought together with their predators. To do so, they are sprayed with a solution containing fungal spores or nematodes.
Despite the promising approaches, it will still take several years before it is possible to effectively combat the ticks with their natural enemies. ”This type of research takes a very long time and we have to be patient because we are combining several organisms and must take care not to harm or even kill useful organisms,” said Mackenstedt highlighting that third-party funds are required to continue the project. The three-year funding provided by the Landesstiftung Baden-Württemberg Foundation helped the scientists to achieve the first results, but in order to continue their work with the same effectiveness, the scientists hope that new funds will be granted.
Mackenstedt assumes that they will require another two to five years before the project is ready for application. Then it should be possible to reduce the number of ticks in particularly hazardous areas such as around forest kindergartens, playgrounds and paths. ”We do not believe that we will be able to kill all the ticks in Baden-Württemberg, but I am sure we will be able to reduce the number of ticks in some areas. Ticks on their own do not migrate over long distances, although they do cover long distances when attached to their rodent hosts,” said Mackenstedt.
Wasps as a potential third remedy
Independently from the project funded by the Landesstiftung, researchers at the University of Hohenheim are focusing on another tick adversary. Professor Dr. Johannes Steidle at the Institute of Zoology at the University of Hohenheim works together with Mackenstedt on the use of wasps for the eradication of ticks. ”Ixodiphagus is a wasp species that is a parasite on ticks. It used to be found only in the area around Bratislava in Slovakia and the Lueneburg Heath in Northern Germany, but has now also been discovered in the Stuttgart area,” said Mackenstedt. The two researchers will continue to look at the tick-killing potential of the wasps despite not receiving Landesstiftung funds. ”The use of wasps have the advantage that no undesired side effects would be expected,” said Oehme highlighting the benefits of this wasp species.
leh - 08.10.2007
© BIOPRO Baden-Württemberg GmbH
University of Hohenheim
Institute for Zoology, Dept. of Parasitology
Prof. Dr. Ute Mackenstedt
Tel.: +49 (0)711 459-22275
Fax: +49 (0)711 459-22276