Naturally-occurring entomopathogenic fungi on three bark beetle species (Coleoptera: Curculionidae) in Bulgaria

Abstract

Bark beetles (Coleoptera: Curculionidae: Scolytinae) belong to one of the most damaging groups of forest insects and the activity of their natural enemies - pathogens, parasitoids, parasites or predators suppressing their population density, is of great importance. Biodiversity of entomopathogenic fungi on bark beetles in Bulgaria has been investigated sporadically. The aim of this preliminary study was to find, identify and study morphological characteristics of fungal entomopathogens naturally-occurring in populations of three curculionid species - Ips sexdentatus Boern, Ips typographus (L.) and Dryocoetes autographus (Ratz.). Dead pest adults were found under the bark of Pinus sylvestris and Picea abies trees collected from forests in the Maleshevska and Vitosha Mountains. Fungal pathogens were isolated into pure cultures on SDAY (Sabouraud dextrose agar with yeast extract) and were identified based on morphological characteristics both on the host and in a culture. Morphological characteristics of the isolates were studied by phenotypic methods. The fungal isolates obtained from dead adults of Ips sexdentatus, Ips typographus and D. autographus were found to belong to the species Beauveria bassiana (Bals. - Criv.) Vuillemin, Beauveria brongniartii (Saccardo) Petch and Isaria farinosa (Holmsk.) Fries (anamorph Ascomycota, Sordariomycetes: Hypocreales, Cordycipitaceae). Morphological traits of the isolates are described.