Extremely low infection levels of pathogens and nematodes in Trypodendron spp. (Coleoptera: Curculionidae)

The striped ambrosia beetles Trypodendron lineatum and T. domesticum are timber forest pests in the Palearctic region and North America. Because only a few pathogens are known for Trypodendron species, the aim of this work was to determine the spectrum of pathogen species of T. lineatum, T. laeve, and T. domesticum. Trypodendron species were collected in pheromone traps at nine localities in the Czech Republic, five localities in Poland, and one locality in Austria. In total, 2,439 T. lineatum, 171 T. domesticum, and 17 T. laeve beetles were dissected and examined. Infection was found in only two of the 17 specimens of T. laeve and in only two of the 171 specimens of T. domesticum; in all four cases, the parasites were nematodes. Parasitisation of T. lineatum by nematodes was found in T. lineatum at eight localities with a mean (± SE) parasitisation level of 8.1 ± 4.7%. A Chytridiopsis sp. was detected in cells of the midgut epithelium of one T. lineatum specimen, and Gregarina sp. was detected in the midgut lumen of two T. lineatum specimens; no other pathogens were found in T. lineatum. The low infection rates and the tendency for infection by nematodes can be explained by the monogamy of Trypodendron spp. and their feeding on fungi in short galleries that are not connected to the galleries of conspecifics.