Phoretic mite communities associated with Ips typographus and Ips duplicatus (Coleoptera: Scolytinae) in a Norway Spruce stand.

European spruce bark beetle Ips typographus (Linnaeus 1758) (Scolytinae) is considered the most destructive and aggressive pest of Norway spruce in Europe. Recently, Ips duplicatus (Sahlberg 1836) (Scolytinae), another species of bark beetle, that also affects Picea trees, has expanded its range westwards in Europe. In spruce stands, bark beetle populations are closely associated with various organisms such as fungi, nematodes, and mites. While phoretic mites and their relationship with I. typographus have been extensively studied in Europe, only single study has focused on the populations of phoretic mites associated with I. duplicatus. The aim of this study is to analyze and document the communities of phoretic mites and their complex relationships with these two bark beetles species. The research was conducted in a stand located at the lower limit of spruce, where the two pest species have developed outbreaks together. Over 50,000 beetles were collected using wing-type pheromone traps, of which 4,348 were analyzed for the determination of phoretic mites (2,413 I. typographus; 1,935 I. duplicatus). In total, nine species of phoretic mites were identified, of which only six were found on Ips duplicatus. Among the nine species, Dendrolaelaps disetus Hirschmann, 1960 (Digamasellidae), Elattoma sp. (Pygmephoridae), and Paraleius leontonychus Berlese, 1910 (Oribatulidae) are reported for the first time in Romania. The results showed that although Ips typographus beetles carried significantly more phoretic mites than Ips duplicatus throughout the entire flight period, both species exhibited similar peaks in phoresy rate. ONE-WAY PERMANOVA test revealed significant differences between the two phoretic mite communities, differences also highlighted by diversity indices. These differences are most likely due to the presence of certain mite species only on I. typographus beetles, as well as differences between the populations of common species. The phoretic attachment location on host beetles varied across mite and host beetle species.