Fungal and mite associates of the fir bark beetle Pityokteines spinidens

Pityokteines spinidens commonly occur in Europe where they infest Silver fir and occasionally other conifers. Together with two additional Pityokteines species (P. curvidens and P. vorontzowi) they have been reported as an important factor in Silver fir decline in some parts of Europe. Some ophiostomatoid fungi associated with bark beetles display high levels of virulence to their host trees and they are thus suspected to aid their bark beetle vectors in overcoming the defense mechanisms of living hosts. Increased local populations of P. curvidens, P. spinidens and P. vorontzowi have been recently noted in conifer forests in various parts of Croatia, resulting in high damage levels on Silver fir. This increase in importance of Pityokteines species as forest pests of Silver fir in Croatia, prompted research on the biology of these bark beetles species and on their mite and fungal associates. Six ophiostomatoid fungi were isolated from the galleries of P. spinidens. These included Ceratocystiopsis minuta, Ceratocystiopsis cf. alba, Graphium cf. fimbriisporum, Ophiostoma cf. cucullatum, Ophiostoma piceae sensu lato and a Pesotum species. A total of 8 mite species were documented as associates of P. spinidens: Dendrolaelaps quadrisetus, Uroobovella ipidis, Tarsonemus minimax, Histiostoma piceae, Paraleius leontonychus, Proctolaelaps hystricoides, Trichouropoda lamellosa and Ereynetes scutulis. Mites phoretic on bark beetles can be involved in complex symbiotic interactions with bark beetles and fungi, therefore this research may form the basis for further studies on multilevel interactions between these organisms.