Vectors of Dutch Elm Disease in Northern Europe

Potential Dutch elm disease vector beetle species were caught with pheromone bottle traps and handpicked in 2019: in total, seven species and 261 specimens were collected. The most common was Scolytus triarmatus, but by percent, the incidence of Ophiostoma novo-ulmi was highest in Scolytus scolytus, followed by Xyleborinus saxesenii and S. triarmatus. We analysed the beetles’ DNA using PacBio sequencing to determine vector beetles of Ophiostoma novo-ulmi. Ophiostoma novo-ulmi was found on six out of seven analysed beetle species: Scolytus scolytus, S. triarmatus, S. multistriatus, S. laevis, Xyleborinus saxesenii and Xyleborus dispar. The last two beetles were detected as vectors for Ophiostoma novo-ulmi for the first time. Previous knowledge on the spread of beetles is discussed.

Bursaphelenchus michalskii sp. n. (Nematoda: Aphelenchoididae), a nematode associate of the large elm bark beetle, Scolytus scolytus Fabr. (Coleoptera: Curculionidae), in Dutch elm disease-affected elm, Ulmus laevis Pall.

Summary Bursaphelenchus michalskii sp. n. is described from the bark of the European white elm, Ulmus laevis. All propagative stages of the nematode were found in larval galleries of the large elm bark beetle, Scolytus scolytus, and in overlapping gallery systems of this species and the small European elm bark beetle, S. multistriatus. Dauer juveniles of the new nematode are transmitted to new breeding trees under elytra of adult S. scolytus. Bursaphelenchus michalskii sp. n. is characterised by the female body length of 953 (838-1108) μm and male body length of 893 (811-971) μm, very slender body (a = 53.9 (46.1-58.5) and 60.9 (52.2-72.0) in female and male, respectively), lateral fields with three incisures (two bands), excretory pore usually located anterior to the median bulb, lack of vulval flap, long post-uterine sac, relatively small spicules 12.3 (10.8-13.3) μm long with no cucullus and with distinct, somewhat thorn-like, dorsally bent or reflexed condylus and a conical or digitate rostrum, and the arrangement of the seven male caudal papillae (i.e., a single precloacal ventromedian papilla (P1), one pair of adcloacal ventrosublateral papillae (P2) at or just anterior to cloacal slit, one ventrosublateral, postcloacal pair (P3) located at ca 60% of the tail length, posterior to cloacal slit, and one pair (P4) of ventrosublateral papillae located near the base of the bursa). The newly described species shares most of the key morphological characters with members of the eremus-group (sensu Braasch et al., 2009). However, B. michalskii sp. n. is unique amongst Bursaphelenchus species by a combination of female tail and spicule shape, excretory pore position, and other morphometric characters. These findings were confirmed by DNA sequencing and phylogenetic analysis of the 18S and 28S rDNA regions and by the unique molecular profile of the ITS region (ITS-RFLP).

Dendrometric, phytopathological and entomological characteristics of a wych elm tree on mt. Goc

Valuable broadleaves, including also wych elms, belong to the category of rare tree species in the growing stock of Serbia. The conservation of Serbian forest diversity and the genetic potential of these tree species require a multidisciplinary study. In this respect, we undertook a dendrometric and health analysis of a wych elm tree on Goc, as it is a rarity by its dimensions, not only from the local, but also from the regional aspects. The tree is 266 years old, its diameter at breast height is 2.09 m, height 42.1 m, and volume (d>3 cm) 56.35 m3. Current height increment culminated early, at the age of 20-30 years, attaining 0.5 m, and current diameter increment at the age of 40-50 years when its value was 14.4 mm. The above data point to a high productivity of this elm tree and to favourable site and stand conditions of its development. On the other hand, its current diameter increment and height over the last period (1.7 mm, and 0.03 m respectively) indicate that the tree was in the phase of physiological dying. 10 species of fungi were identified on the tree (facultative parasites or saprophytes), the most significant being Armillaria mellea and Aurantioporus fissilis, which caused central heartwood decay. Other fungi developed saprophytically in the dead part of the stem or in dead branches. Eight insect species (secondary and tertiary pests) were identified, including the two most dangerous elm beetles (Scolytus scolytus and S. multistriatus). Together with the species Saperda punctata and Cerambyx scopolii, they accelerated the dying process of twigs and branches, as well as of the whole tree. Ambrosia beetle Xyleborus monographus infested the stem and the large dead branches and caused minor technical damage in wood. The species Dorcus paralelopipedus, Oryctes nasicornis and Valgus hemipterus supported the faster progress of wood-rotting fungi and thus contributed to physiological weakening and shortened the life cycle of the study elm tree.

Distribution and spread of bark beetles (Coleoptera: Scolytidae) around the Gulf of Finland: a comparative study with notes on rare species of Estonia, Finland and North-Western Russia

Along-term faunistic study of bark beetles (Coleoptera: Scolytidae), conducted in Estonia, as well as in Karelia, Leningrad (St. Petersburg) and Murmansk provinces of Russia, enables a comparison of the species composition of bark beetles in the regions bordering Finland. Altogether the distribution patterns of 83 species of scolytids are examined. The northern borders of the distribution range for Scolytus scolytus, S. multistriatus, S. laevis, Hylastes ater, H. opacus, Orthotomicus longicollis, Pityogenes trepanatus, Ips amitinus and Cryphalus abietis in Northern Europe are redefined. The list of bark beetles for Estonia and North- Western Russia (Karelia, Leningrad and Murmansk provinces) with their occurrence in some biogeographical provinces of Fennoscandia (Ik, Kl, Kon, Ks, Kk, Lim) is given. Recent records of bark beetles, endangered or rare in Finland, and their current distribution in the neighbouring regions are discussed.