Studies of this sort have previously been implemented in some European countries, and in the US a commercial strain of one such pathogen has been approved as the basis for biologics used to control tick numbers in rangelands. These foreign studies however targeted other tick species, while this effort is the first one for the taiga tick.
Lyubov Bespyatova on a ‘flagging’ survey. All in all, scientists collected a thousand ticks
Nine strains of three species of entomopathogenic fungi capable of developing under the low temperatures typical of late May and early June – when the activity of adult taiga ticks in Karelia is at its peak – were selected for the experiment. This project phase was implemented by Boris Borisov, a well-known mycologist, Leading Researcher of the Laboratory of Microbiological Means of Plant Protection at AgroBioTechnology company, Moscow. He prepared isolates (cultures of microorganisms derived from a specific source) of fungi collected in the Arkhangelsk, Magadan, Irkutsk, Moscow Regions, Krasnodar Krai, and Abkhazia, whose spores have been retrieved from infected insects, including ticks.
Karelian scientists – researchers from the Laboratory of Animal and Plant Parasitology of the Institute of Biology KarRC RAS Lyubov Bespyatova and Sergey Bugmyrin, were in charge of the field-lab experiment carried out at a research station in the Kondopoga District of the republic.
– The laboratory part of this study was made possible by the basic research that started back in the mid-20th century. The research theme “Predators and parasites of blood-sucking arthropods” was initiated by the founder of our laboratory, Dr. Aino Lutta. After completing the doctoral course in Leningrad, she was sent to Karelia to investigate the agents transmitting dangerous human and animal infections, first of all human tick-borne encephalitis and babesiosis of cattle, – recollects Lyubov Bespyatova, trained mycologist, Senior Researcher of the Institute of Biology KarRC RAS, whose doctoral thesis dealt with diseases affecting horse flies infected with entomopathogenic fungi.
Ticks were sampled in May in the woods by flagging, i.e. onto a special piece of cloth. The sample was divided into the control and the experimental groups, which were placed in test tubes with identical temperature and humidity corresponding to those in the natural environment. The experimental groups were first infected with strains of different species of entomopathogenic fungi.
The experiment continued for three weeks. During this time, tick mortalities were constantly monitored. In the control (uninfected group), the first ticks started dying after a week and average mortality in the group by the end of the experiment rose to 15.6%. In most of the experimental groups, the mortality rate was higher than in the control already on the seventh day, indicating the pathogen was actually affecting the ticks.
Authors of the study (left to right): Boris Borisov, Sergey Bugmyrin, and Lyubov Bespyatova
The seventh day was also when isolate-specific differences in mortality began showing. Ultimately, the highest effect, significantly ahead of the rest in inducing mortalities, was demonstrated by an isolate of the fungus Beauveria bassiana, collected from a weevil on Bolshoy Solovetsky Island in the Arkhangelsk Region. After a week into the experiment, average mortality among ticks in this treatment exceeded 45%, rising to 79% after nine days and 95% after eleven days. An isolate of Beauveria bassiana from the Magadan Region “caught up” only by the seventeenth day. The rest of the isolates also caused the death of the arthropods, but less efficiently.
Interestingly, tick males and females differed in susceptibility to fungal infections: mortalities among males occurred sooner. In some treatments, the difference after nine days was over 20%. By the end of the experiment however, it was nearly smoothed out.
The results of the study were published in the international journal Entomological Review and presented at multiple conferences of different levels. The experiment serves as a first step in the assessment of the efficacy of entomopathogenic fungi in addressing the ixodid tick issue.
Experimental groups of ticks in Petri dishes
The articles states that the acaricidal activity of the different isolates of entomopathogenic fungi in this study was assessed in the laboratory at constant 100% humidity ideal for the development of mycoses. Further real-life experiments in the field are needed to objectively evaluate the practical feasibility of implementing the biological control of ixodid ticks.
– We must be very cautious when trying to control the numbers of certain species, being mindful of the future consequences. It feels right and wise to use the region’s own biological objects, i.e. entomopathogenic fungi, for the population control, – noted Lyubov Bespyatova.
On the other hand, the scientist is convinced that the key to combating dangerous tick-borne infections today is non-specific prevention and individual precautions. In addition to getting timely vaccination, it’s important to keep up the immunity and use the available knowledge on the biology and ecology of ixodid ticks in the region.
