Pathogens and nematodes associated to three bark beetle species of the genus Orthotomicus (Coleoptera Curculionidae) in central-south Europe

The aim of the research was to determine the occurrence of insect’s pathogens and nematodes in Orthotomicus laricis (F.), Orthotomicus erosus (Wollaston), and Orthotomicus nobilis (Wollaston) in central-south Europe. We found three insect’s pathogens Chytridiopsis sp., Gregarina sp., Mattesia sp. and nonspecific gut nematodes and nematodes in the haemolymph, where adult nematodes were identified as Contortylenchus laricis (Fuchs). A total of 1,183 beetles from galleries in pine bark were dissected and examined; these included 912 O. laricis beetles from seven localities, 164 O. erosus beetles from three localities, and 107 O. nobilis beetles from one locality. At one locality, microsporidium Chytridiopsis sp. was detected in almost 15% of the O. laricis beetles. Protozoan pathogen Gregarina sp. was found in O. laricis beetles at three localities, but its incidence did not exceed 5%. Chytridiopsis sp., Gregarina sp., and neogregarine Mattesia sp. were detected in O. erosus beetles at one of three localities. No pathogen was found in O. nobilis. The genus Mattesia was reported in an Orthotomicus species for the first time. The incidence of pathogens and nematodes in the three Orthotomicus species seemed unrelated to the beetle species: the deposition of eggs singly or in clusters, the ability to outbreak, or the beetle distribution range. A literature review and the current results indicated that the number of pathogens detected in a particular species of pine bark beetle is related mainly to the number of specimens examined.