A new species,Bursaphelenchus ulmophilussp. n., from thehofmannigroup is described morphologically and molecularly. This nematode species was found associated with Dutch elm disease ofUlmusglabrain parks of St Petersburg, Russia, and is vectored by adults and larvae of the bark beetlesScolytusmultistriatusandS. scolytus.Bursaphelenchus ulmophilussp. n. is characterised by the following features: body length 600-850 μm, stylet 12-14 μm long with base slightly and smoothly expanded, but lacking knobs, median bulb almost spherical in female and slightly ovoid in male, pharyngeal gland lobe dorsal, 4-5 body diam. long. This species has an oval spermatheca filled with spherical nucleic sperm 4-5 μm diam. Female post-uterine sacca0.5 of the vulva-anus distance andca3 vulval body diam. long, female tail reflexed, strongly hooked ventrally with a digitate or conically rounded tip. The male has seven caudal papillae arranged as 1 + 2 + 2 + 2, P1 is unpaired, anterior to cloacal opening, paired P2 at cloacal aperture, paired P3 and paired pore-like ‘gland papilla’ P4 at the lateral edges of the bursa which has the posterior border rounded to truncate. Phylogenetic analyses of the D2-D3 of 28S rRNA, partial 18S rRNA and ITS rRNA gene sequences revealed thatB. ulmophilussp. n. formed a clade with species of thehofmannigroup and shared close relationships withB. hofmanniandB. pinasteri.

In this study juvenile stages of Bursaphelenchus crenati (Sexdentati group) were distinguished based mainly on the genital primordium structure. Dauer stage juveniles were sampled under elytra of Hylesinus crenatus in galleries in bark of the wilted Fraxinus excelsior in the Voronezh region of Russia and were multiplied in laboratory cultures on the fungus Botrytis cinerea. Individual development included five stages (J1-J4 and adults) separated by molts. The first molt J1 to J2 occurred inside the egg and the J2 was at the hatching stage. Sex of juvenile stages can be identified using the morphology and size of the genital primordia and a body size of nematodes. Sex of juveniles may be identified from the J3 stage by the presence of the cloacal primordium in male juvenile and orientation of the germinal zone of the genital primordium. A tabular key to developmental stages of B. crenati is given. The body grows during molts and within each stage. The body increases rapidly after J3 stage combined with the most active cellular differentiation and elongation of the genital primordium. The dauer juveniles collected from elytra of vector beetles were similar to the third juvenile stage of the propagative generation by genital primordium structure and body size.

Summary: To develop models of forest ecosystem functioning, it is necessary to estimate parameters of the population dynamics of nematode species. Parameters of ontogenesis of Bursaphelenchus willibaldi from oak in culture of the fungus Botrytis cinerea were determined in vitro: oviposition began 2.7 (1-3) days after inoculation with adult nematodes; timelines of juvenile formation were: second-stage juveniles: 3.2 (3-4) days, third-stage juveniles: 3.6 (3-5) days, fourth-stage juveniles: 4.8 (3-6) days, first generation (1G) ended with a J4 moulting to adult after 5.8 (4-6) days. One day after the formation of the first generation, nematodes left the 2% potato-sugar agar (PSA) medium with the feed fungus and moved upwards, forming a migratory group (MG). In PSA the total nematode abundance reached peaks on day 11 (2G) and in the MG on day 27 (4.5G). The fecundity of females during population growth was determined as 3.4 (2.1-5.9) eggs day⁻¹ and a model of exponential population growth was developed for total nematodes , ; and for females , . Under conditions of unrestricted reproduction and temperature of 21-23°C, the nematode and fungus can colonise 1 m³ of PSA-like medium in 36.8 days. The survival stage in the propagative generation was presumably J4. The female lifespan consists of a feeding and reproductive phase in the PSA (6 days) and a survival phase in the MG (1 month to 1 year). In MG, nematodes formed swarming groups of 20-200 individuals.

A new nematode species, Bursaphelenchus ussuriensis sp. n. is described in the bark beetle–elm tree association (Scolytus jacobsoni and Ulmus davidiana var. japonica f. suberosa) in the Asian Pacific region of Russia. The new species belongs to the Hofmanni group of Bursaphelenchus and is closest to B. ulmophilus. Its characteristics are as follows: lateral field with three incisures, body length 497–771 µm, post-uterine sac 3.6–5.4 times vulval body diam, 56 (39–66)% of vulva–anus distance, and spicule length 10.3 (9.5–12.5 µm). The new species differs from all species of the Hofmanni group in the closely situated P3 and P4 male caudal papillae and the GP5 small ‘glandpapillae’ pair on the butterfly-like papillae plate, in the set of P1, P2, P3, P4, GP5; vs. in all other species, the P4 papillae pair is absent in the pattern of P1, P2, P3, GP5. The phylogenetic position of B. ussuriensis sp. n. with other species of the Hofmanni group were reconstructed using the D2–D3 expansion segments of 28S and ITS rRNA gene sequence analysis. Sequences of twelve mitochondrial protein-coding genes of B. cocophilus, B. fraudulentus, B. michalskii, B. ussurensis sp. n., and B. willibaldi were obtained in this study. Phylogenetic relationships among eighteen Bursaphelenchus species based on the analysis of the mtDNA sequence dataset are provided and discussed. A modified diagnosis of the Hofmanni group is proposed.

В лабораторных условиях протестирована специфичность трех видов нематод рода Bursaphelenchus: B. willibaldi (Fungivorus), B. ulmophilus (Hoffmanni), B. michalskii (Eggersi) к трем видам древесных растений: Picea abies, Acer platanoides, Fraxinus excelsior. Тест был направлен на выявление независимой от переносчика специфичности нематод к разным растениям. Эксперимент проводили на саженцах в закрытом грунте в лабораторных условиях. Изоляты нематод хранились в банке живых культур Зоологического института РАН. Перед постановкой теста черви были размножены в стерильной культуре гриба Botrytis cinerea. В качестве инокулята для заражения саженцев использовали 200 особей нематод одного вида разных стадий развития на растение. Эксперимент проводился при температуре 21–23 °C на протяжении 45 дней. Параметр успешного размножения – превышение финальной численности нематод над инокулюмом. Вид B. willibaldi продемонстрировал выживаемость на всех трех видах экспериментальных растений, однако превышение численности нематод по сравнению с инокулюмом не было зафиксировано. Вид B. ulmophilus выжил на P. abies и A. platanoides. На F. excelsior вид B. ulmophilus не выжил. Вид B. michalskii через 45 дней после инокуляции не обнаружен ни в одном из зараженных растений. Это свидетельствует о том, что данный вид нематод не способен выживать на представленных видах растений. Вероятность возникновения независимой от переносчика специфичности трех представленных видов нематод к протестированному кругу растений является низкой. The specificity of three species of nematodes of the genus Bursaphelenchus: B. willibaldi (Fungivorus), B. ulmophilus (Hoffmanni), B. michalskii (Eggersi) to three species of woody plants: Picea abies, Acer platanoides, Fraxinus excelsior was tested in laboratory conditions. The test was aimed at identifying the vector-independent specificity of nematodes to host plants. The experiment was conducted on indoor seedlings under laboratory conditions. Nematode isolates were stored in the live culture bank of the Zoological Institute of the Russian Academy of Sciences. The worms were cultured in a sterile culture of the fungus Botrytis cinerea before the test was set up. As an inoculum for infecting the seedlings, 200 individuals of the same species of nematodes at different developmental stages were used per plant. The experiment was conducted at 21–23 °C for 45 days. The parameter for successful reproduction is the excess of the final nematode population over the inoculum. The species B. willibaldi demonstrated survival on all three experimental plant species, but no excess of nematodes compared to the inoculum was recorded. B. ulmophilus survived on P. abies and A. platanoides. B. ulmophilus was not detected on F. excelsior. B. michalskii was not detected in any of the infested plants 45 days after inoculation. This indicates that this nematode species is not able to survive on the plant species represented. The probability of vector-independent specificity of the three submitted nematode species to the tested range of plants is low.

Summary: The copulatory organs and pharynx are important for nematode classification. This research aimed to study the musculature of the wood-inhabiting nematode, Rhabditolaimus ulmi, using confocal microscopy. The lip region is hexagonal with enlarged lateral lips; the pharynx is diplogastrid type with two bulbs. The corpus comprises the fused stegostoma, procorpus and metacorpus, with six glands opening in the stegostoma and the corpus limen. The stegostoma has a large dorsal bulge and the posterior bulb is devoid of valve, with two circles of dilators and a basal sphincter. The female genital muscles have a four-radial symmetry around the vaginal opening to the uterus. Two vaginal constrictors and four pairs of dilators of two types are connected to the vagina-uterus opening; four dilators run perpendicular to the uterus axis and are connected to the uterine muscular corset. The sphincter between the intestine and cloaca consists of the middle ring with two pairs of processes connected ventrally with intestinal fasciculi and dorsally with the body wall. The ring contains the inner biconical X-structure. In the male, the gubernaculum has the dorsal erector and a pair of transverse muscles. The wide gubernacular spicule protractor envelops spicules anteriorly. The ventral tail muscle is wide, unpaired, and nine pairs of serial diagonal muscles are located beneath the body wall muscles, followed by three pairs of postcloacal oblique muscles of the tail. Anal depressors comprise a pair of transverse muscles with expanded middle globular parts. The copulatory muscles are of the Rhabditidae and Cephalobidae type modified because of spicules elongation. The muscle characters code of the previously published tabular key for 15 muscle characters is 73422-22144-42223; it can be used for phylogenetic reconstructions.