Nematode parasitism is a yield limiting factor in many cropping systems, including potato production, which can translate into substantial economic losses. These impacted financial returns are simply calculated by subtracting the cost of production from total revenue (yield times the price per yield of potatoes). The production costs can include, but are not limited to, chemical and biological control agents. To assess economic returns associated with different nematode management strategies, we evaluated complete cost estimations for a representative commercial potato farm in central Michigan, USA. Economic returns were calculated using stochastic parameters for two biological control agents (MeloCon and Majestene), six chemical controls (Mocap, Movento, Nimitz, Velum and Vydate), and two soil amendments (poultry and dairy manure). Evaluated costs included stochastic estimations for price per unit weight of potatoes, fuel, labour and production land rent. Yield data from three field trials were used to create empirical distributions. Using yield data and stochastic cost estimations, we generated 500 simulations of net returns per treatment. The top three average returns were obtained from the use of Mocap, Nimitz and poultry manure. Velum, Movento, dairy manure and Vydate also gave returns significantly higher than no treatment at all; however, the biological nematicide, Majestene, showed negative returns. This simple financial model is a crucial layer of analysis on the performance of nematicides that can be adapted to advise growers through Agricultural Extension activities and needs to include the evaluation of biological control agents.
Cryptaphelenchus paravaricaudatus n. sp., from declining Pinus massoniana in China, is described and illustrated. The new species is characterised by the 233-308 μm long females with distinctly annulated cuticle, lateral fields with four lines, lip region separated from the body by a shallow depression, delicate stylet with small knobs, post-vulval uterine sac short and rectum and anus invisible. Males are 204-259 μm long, with spicules 8.5-12.0 μm long, condylus well developed and broad, caudal papillae arranged as a single (P1) and a pair of precloacal papillae (P2) plus two pairs of postcloacal papillae (P3 and P4). Based upon the general morphology of the female, the new species most closely resembles C. varicaudatus. The morphological differences with the aforementioned species and other species having similar morphology are discussed. The phylogenetic analyses based on small (SSU) and large subunit (LSU) D2-D3 expansion segments of ribosomal DNA (rDNA) of different individuals of the new species revealed that it fell into the clade of Cryptaphelenchus in both SSU and LSU trees. The monophyly of the genus was retained.
A new nematode species was recovered from the syconia of Ficus semicordata from Xishuangbanna Tropical Botanical Garden, Yunnan Province, China. It is described herein as Martininema semicordatae n. sp. and is characterised by having the combined characters of a long post-vulval uterine sac, excretory pore located at nerve ring level, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip with mucron, absence of gubernaculum (= apophysis), and a recurved, rose-thorn-shaped spicule lacking a terminal cucullus. Martininema semicordatae n. sp. differs from other sequenced species by differences in the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with LSU D2-D3 expansion segment sequences suggested that M. semicordatae n. sp. is clustered in a highly supported monophyletic clade with M. guangzhouense, M. fistulosus and M. baculum, and shares a common ancestor with these three species.
In this study, we provide morphological and molecular characterisation of three known species of the Criconematoidea, namely Criconema cylindraceum, Paratylenchus alleni and P. steineri, recovered from Iran. Descriptions, morphometric data, drawings and photomicrographs are provided, and comparisons are made with closely related species. Phylogenetic analysis using the D2-D3 expansion segments of the 28S rRNA gene revealed that C. cylindraceum formed a cluster with Ogma decalineatus, a species with a similar head structure, but with differences in cuticle ornamentation, tail shape and morphometric characters. Moreover, P. alleni grouped with species of Paratylenchus having four lateral lines and a short stylet (< 40 μm), exceptionally including the unresolved P. straeleni, while P. steineri formed a clade with long stylet species, including P. teres and P. wuae. The taxonomic placement of C. cylindraceum in Criconema, rather than in Criconemoides, is justified, and P. teres is molecularly differentiated from P. steineri, the two species differing in having or lacking a stylet in the fourth-stage juvenile.
The endomigratory root-lesion nematode, Pratylenchus scribneri, is one of the major plant-parasitic nematodes infecting potato. Accurate identification and quantification of this nematode are essential to develop management strategies but microscopic observations are particularly challenging and time consuming. In this study, a SYBR Green I-based real-time quantitative polymerase chain reaction (qPCR) assay was developed to detect and quantify P. scribneri from field soil DNA extracts. A primer set was designed from the internal transcribed spacer (ITS) region of the P. scribneri rDNA gene. Primer specificity to the target nematode was evaluated by both in silico analysis and qPCR and no detection or non-specific amplification was observed for other non-target nematode species/communities tested in this study. Standard curves were generated using DNA extracts from autoclaved soil infested with varying nematode numbers for calibration. The curves were supported by a high correlation between the P. scribneri numbers artificially added to soil or estimated from naturally infested field soils by traditional methods, and the numbers quantified using the qPCR assay. The assay was able to detect 1 out of 128 (0.0078) equivalents of the DNA of a single nematode in 0.5 g of soil. The qPCR assay developed in this study provides a specific and sensitive detection and quantification of P. scribneri from field soils and a rapid alternative to time-consuming traditional nematode identification and enumeration.
Stylet (feeding) dimorphism of Bursaphelenchus sinensis was experimentally confirmed during a recent study and its predatory form was considered similar in morphology to species of Berntsenus. Therefore, available type and voucher materials for members of Berntsenus were examined for their morphology and compared with Bursaphelenchus sinensis and B. aberrans, another related species showing feeding dimorphism. The typological characters of their co-habiting aphelenchoidid species were also examined. The type materials of Berntsenus spp. have characteristic squared lips, a thick stylet, large median bulb and short and stout pharyngeal glands; males, when present, have a P1 papilla and a tape-like bursa, suggesting that they are the predatory form of improperly classified Bursaphelenchus species. In addition, Aphelenchoides pityokteini and Ektaphelenchus tenuidens (= Aphelenchoides tenuidens), co-occurring with their respective host bark beetle isolates of Berntsenus, were typologically confirmed to belong to the aberrans-group of Bursaphelenchus and considered to be conspecific to each co-habiting Berntsenus species. Herein, Berntsenus is synonymised with Bursaphelenchus, and Bursaphelenchus brachycephalus n. comb. (= Berntsenus brachycephalus and E. tenuidens) and Bursaphelenchus pityokteini n. comb. (= A. pityokteini and Berntsenus labiosus) are proposed.
To investigate the phoretic association between nematodes in the genus Bursaphelenchus and cerambycid beetles in north-eastern Japan, Pinus densiflora logs were placed in two pine forests in the towns of Yamada and Hiranai as beetle oviposition sites. At 1-2 years after oviposition, adults of Monochamus saltuarius emerged from the logs placed in Yamada and adults of Acalolepta sejuncta and A. fraudatrix emerged from the logs placed in Hiranai, and Bursaphelenchus nematodes were recovered from two of these species (M. saltuarius and A. sejuncta). Morphometrics and a phylogenetic analysis of the internal transcribed spacer regions 1 and 2 and the 5.8S ribosomal RNA gene indicated that both of these nematode populations were B. doui, which has previously only been known to use M. subfasciatus and A. fraudatrix as vectors. Therefore, this study demonstrated that this nematode utilises at least four species of beetles belonging to two genera as vectors in the field.
Ficophagus from collecting trips in eastern Australia, made over 15 years, are summarised and show that species of the genus occurred widely in sycones of Ficus, subgenus Urostigma, section Malvanthera. Two new species (based on morphological differences and molecular sequencing) are described: Ficophagus elizabethae sp. n. from Ficus macrophylla, F. rubiginosa and F. obliqua, and Ficophagus richardi sp. n. from Ficus obliqua; and a morphospecies, Ficophagus Morphospecies malandicus from Ficus obliqua. Ficophagus elizabethae sp. n. is characterised by having the excretory pore (EP) opening from the level of the junction of the conus and shaft of the stylet to that of the knobs, a relatively long procorpus (1.0-2.5 times length of stylet), female tail with an obliquely truncate tail with a hyaline area and a finely to broadly rounded tip which may be mucronate; post-vulval uterine sac (PUS) ca one vulval body diam. (VBD) in length; rose-thorn-shaped spicule with distinct rostrum and prominent condylus; and genital papillae arranged as largest pair adcloacal, second pair posterior to mid-tail length, and third small pair near tail tip; and was collected from Sydney in New South Wales, to Bundaberg in Queensland (QLD). Ficophagus richardi sp. n. is characterised by having the EP opening at the level of the junction of the stylet shaft and conus, a labial cap which is raised around the opening for the stylet; procorpus 0.8-1.7 times length of the stylet, PUS <1 VBD in length, long uterus, and female tail with a V-shaped hyaline area at the bluntly rounded tip; rose-thorn-shaped spicule with a small rostrum and prominent condylus, three pairs genital papillae, first and largest on anterior cloacal lip, second at 70% of tail length measured from cloacal aperture, and third near tip, and was collected from Ban Ban Springs in the south to the Bundaberg region in the mid-north of QLD. In addition, in the absence of pertinent molecular sequences, a morphospecies is described. Ficophagus Morphospecies malandicus is characterised by having the EP opening anterior to the junction of the stylet conus and shaft, procorpus 0.9-2 times length of stylet, a short PUS usually <1 VBD long, short uterus, rose-thorn-shaped spicule with a raised condylus and prominent rostrum, and three pairs of subventral papillae on the tail (one adcloacal, one posterior to mid-tail and one near tail tip); and was collected from the Atherton Tableland, QLD. A table comparing morphological characteristics is provided to help with identification of Ficophagus nematodes from figs of the section Malvanthera in eastern Australia.
A new species of fossil mermithid, Heydenius simulphilus sp. n. (Nematoda: Mermithidae), is described from two parasitic juvenile specimens adjacent to a male black fly (Diptera: Simuliidae) in Baltic amber. It is proposed that the nematodes emerged from their developmental sites in the haemocoel of the black fly host through a wound in the abdomen of the latter, as indicated by the release of a droplet of haemolymph and damaged cuticle. Various internal structures of the nematodes are identified and related to those found on extant developing mermithids. This is the first fossil record of mermithid parasitism of a black fly.
The root-lesion nematode, Pratylenchus penetrans, causes growth reduction in glasshouse-grown lettuce and is mainly controlled by chemical soil disinfestation. Integrated management strategies require more knowledge about the population dynamics and damage threshold densities. We monitored the population during 2.5 years in a commercial glasshouse by sampling soil in the same four 1 m2 spots at 0-30 cm and 30-60 cm depth. The grower grew lettuce in rotation with leek, applied 1,3-dichloropropene in summer and left the field fallow during winter. Growing leek reduced the nematode population slightly but chemical soil disinfestation lowered the numbers drastically, although 41% of the nematodes in the deeper layer survived. Black fallow resulted in a slight increase of the population, probably due to hatching. Two pot experiments with ten densities of P. penetrans were conducted to estimate the damage threshold for a summer and autumn cultivar (‘Cosmopolia’ and ‘Brighton’, respectively). The thresholds for lettuce weight were 669 and 3834 P. penetrans (100 ml soil)−1 in summer and autumn, respectively, but with considerable variability in estimated parameters. The thresholds for root damage were much lower: 204 and 48 P. penetrans (100 ml soil)−1. Nematode numbers did not increase on lettuce in the pot tests (maximum multiplication rate was 0.40) but increased slightly in the commercial setting. These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage.