Biological control of the tick Ixodes ricinus with entomopathogenic fungi and nematodes: Preliminary results from laboratory experiments

In Central Europe, Lyme disease and tick-borne encephalitis (TBE) are transmitted by the tick Ixodes ricinus. In the last years, the prevalence of TBE virus in I. ricinus and also the number of human TBE infections have increased considerably in south-western Germany. A similar development is presumed for Borrelia burgdorferi s.l. For biocontrol of the vector I. ricinus, several options are presently evaluated. Among potential biocontrol agents, entomopathogenic fungi, nematodes, and parasitic wasps are the most promising candidates. In first laboratory experiments, different strains of the fungi Metarhizium anisopliae (five strains), Beauveria bassiana (three strains), and Paecilomyces fumosoroseus (two strains) were tested by placing I. ricinus larvae (fed and unfed) and nymphs (fed and unfed) in Petri dishes with filter paper soaked with conidial or blastospore suspensions (2.4×103 to 9.6×106percm2). Ticks were exposed to the different fungi for at least 35 days in the dark at temperatures of 21–24°C. The best LT50 values for unfed larvae (14 days) and unfed nymphs (21 days) were obtained with blastospores of M. anisopliae 97 at 1.4×106percm2. In order to evaluate the potential of entomopathogenic nematodes, the efficacies of three different species, Steinernema carpocapsae, S. feltiae, and Heterorhabditis bacteriophora, were investigated in the laboratory. I. ricinus nymphs (fed and unfed) and unfed females were placed in Petri dishes containing a wet filter paper with 300 and 600 infective nematode larvae per cm2. Ticks were exposed to the nematodes for at least 15 days in the dark at an average temperature of 25°C. The highest mortality was observed in unfed female ticks treated with S. carpocapsae. Results show that among the fungi tested the most promising control efficacy was obtained with two isolates of M. anisopliae, whereas S. carpocapsae was most successful among the nematodes tested against I. ricinus.