Scolytus spp. associated with elms with symptoms of Dutch elm disease in Poland and the reproductive potential of Scolytus multistriatus (Marsham, 1802) (Coleoptera, Curculionidae, Scolytinae)

Dutch elm disease is caused by a species of Ophiostomatales (Ascomycota), namely Ophiostoma ulmi, O. novo-ulmi and O. himal-ulmi. These pathogens are transmitted by elm bark beetles (Coleoptera, Scolytinae: Scolytus spp., Pteleobius spp., and Hylurgopinus rufipes). This disease has devastated the native population of elms in Europe, North America, and New Zealand. Dutch elm disease was first reported in Poland in 1927 and since, it has been the most frequent cause of tree dieback. The process of tree colonization by species from the genus Scolytus was observed in selected experimental sites in Northern, Central and Western Poland. A total of four tree colonizing species were found including: Scolytus scolytus, S. multistriatus, S. pygmaeus, and S. ensifer. Among them, S. scolytus and S. multistriatus were reported in the greatest numbers and highest frequency. The reproductive potential was determined for S. multistriatus. A very high mortality of the young generation was recorded (86% and 89%), which did not limit the spread of the disease. Preferences for tree colonization and location of feeding grounds were investigated in the case of S. multistriatus. No correlation was found between the stem diameter and the number of maternal galleries, whereas a correlation was observed between the stem diameter and the obtained reproduction index [Ri]. It was highest for sections of trees with diameters of 10-17 cm.