Bioassay of Virulence of Some Entomopathogenic Ascomycetous Anamorphic Fungi to Adult Ixodes persulcatus Ticks under Cool Conditions

Entomopathogenic fungi (EPF) play an important role in the density control of many arthropods in nature. The lethal effects of EPF on ixodid ticks (Ixodidae) have been mainly described for the warm-loving southern species that are mostly absent in Europe. We have performed a laboratory assessment of the virulence of 9 psychrotolerant EPF isolates of Beauveria bassiana s. l. (6), Akanthomyces cf. muscarius (2), and Metarhizium anisopliae s. l. (1) at a moderate mean daily temperature of +14°C against the overwintered adult taiga ticks Ixodes persulcatus, collected at the end of May in Kondopoga Province of the Republic of Karelia. All the tested isolates caused mortality in ticks at this temperature after infection with a concentration of 3 × 10⁷ infectious spores per 1 mL. The most virulent and rapidly acting isolate was B. bassiana s. l. CCi-Ar (SI)14 from Arkhangelsk Province, Bolshoy Solovetsky Island (65°N, 35°E), killing 70% of the ticks in 9 days and 95% in 11 days. Male ticks had a slightly higher death rate from fungal infections. The potential suitability of some EPF isolates for biological control of I. persulcatus at low temperatures, demonstrated in our study, requires confirmation in further tests under real conditions of recreational areas actively visited by humans.