Khuong B. Nguyen

Biosystematics of entomopathogenic nematodes : current status, protocols and definitions

COST Action 819: Entomopathogenic nematodes , supercedes Action 812: Cold active lines of insect parasitic nematodes in Agriculture and Biotechnology . It functions in the field of Agriculture and Biotechnology and began in July 1994 and will end in May, 1999. The main objective is to combine interrelated European expertise to increase the use of entomopathogenic nematodes (EPNs) in integrated pest management and to reduce the need for chemical control. Coordination of the Action is the responsibility of a management committee in accordance with a Memorandum of Understanding, which has been signed by representatives of 17 countries: Austria, Belgium, Czech Republic, Finland, France, Germany, Hungary, Ireland, Italy, The Netherlands, Norway, Poland, Portugal, Spain, Sweden, Switzerland and the UK. A research institute in Israel is also participating. Over 40 research institutions and 10 commercial companies participate in Action 819. The EU funding meets the costs related to coordination including the scientific secretariat, workshops, management committee and working group meetings, publications, short term scientific missions and evaluations.

Entomopathogenic nematodes: systematics, phylogeny and bacterial symbionts.

The volume deals with history, morphology, taxonomy, and systematics of entomopathogenic nematodes (EPN) in the families Steinernematidae and Heterorhabditidae, molecular methods and bacteria associated with these nematodes.

Survey of entomopathogenic nematodes and fungi endemic to pecan orchards of the Southeastern United States and their virulence to the pecan weevil (Coleoptera: Curculionidae).

Abstract The pecan weevil, Curculio caryae (Horn), is a major pest of pecans in the Southeastern United States. Entomopathogenic nematodes and fungi are potential alternatives to chemical insecticides for C. caryae control. Our objective was to survey pecan orchards in the southeastern United States for entomopathogenic nematodes and fungi and determine the virulence of the new isolates to C. caryae larvae. Soil was collected from 105 sites in 21 orchards in Arkansas, Georgia, Louisiana, and Mississippi. Entomopathogens were isolated by exposing soil to C. caryae and greater wax moth larvae, Galleria mellonella, (L.). We isolated entomopathogenic fungi and nematodes from 16 and 6 of the 21 orchards surveyed, respectively. The entomopathogenic fungi included Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin, and nematodes included Heterorhabditis bacteriophora Poinar, Steinernema carpocapsae (Weiser), Steinernema glaseri (Steiner), and Steinernema rarum (Doucet). This is the first report of Steinernema rarum in the United States. Soil characteristics in orchards were analyzed for pH, organic matter, and nutrients; we detected a negative relationship between fungal occurrence and manganese levels in soil and a positive relationship between M. anisopliae occurrence and calcium or magnesium levels. In laboratory assays, virulence of 15 nematode and 22 fungal isolates to C. caryae larvae was tested in small plastic cups containing soil. Results indicated poor susceptibility of the C. caryae larvae to entomopathogenic nematodes. Several fungal isolates that caused significantly higher mortality in C. caryae larvae than other strains (including a commercial strain of B. bassiana) should be investigated further as potential control agents of C. caryae.

Scanning Electron Microscope Studies of Steinernema Glaseri (Nematoda: Steinernematidae) 1

Scanning electron micrographs are presented of Steinernema glaseri. The male head of S. glaseri is slightly swollen and bears six labial and four large cephalic papillae. There are 11 pairs of genital papillae plus a single papilla. The spicule is unique with a short head, distinct shaft, long and narrow blade, and a spicule tip which has a ventral aperture and appears hook-like. A velum was not observed. The gubernaculum is much shorter than the spicule, with the anterior end curved ventrally, and enlarged gradually posteriorly. Usually, the capitulum and cuneus are forked anteriorly to form a Y-shaped structure. The female head has six labial and four cephalic papillae, and the vulva may be with or without a thickened flap. The lateral field pattern of the infective juvenile begins anteriorly with one incisure which after a short distance becomes three, six, seven and nine incisures which create two, five, six and eight ridges, respectively. At about the level of the phasmids, the number of ridges gradually decreases to two broad ridges.

Steinernema khoisanae n. sp. (Rhabditida: Steinernematidae) : a new entomopathogenic nematode from South Africa

A new species of entomopathogenic nematode, Steinernema khoisanae n. sp. is described from South Africa. The new species is characterised by morphometrics of the infective juvenile with body length 1076 μm, narrow body diameter of 33 μm, excretory pore 94 μm from anterior end, tail 85 μm long, a = 33, D% = 68, H% = 57, and E% = 111. The lateral field pattern of the new species is 2, 7, 8, 6, 4 and 2. The male of the first generation can be recognised by the spicule and the gubernaculum shape, excretory pore located posteriorly near the end of the pharynx, D% = 88, and SW% = 199. The first generation female can be recognised by the non-protruding vulva and tail bearing a prominent mucron. Steinernema khoisanae n. sp. is characterised genetically by sequences of the internal transcribed spacers and D2/D3 regions of 28S ribosomal DNA, by composition of their sequences and by numerous unique, derived, nucleotide character states. Phylogenetic trees show that S. khoisanae n. sp. and other members of the S. glaseri-group form a monophyletic assemblage.

Heterorhabditis safricana n. sp. (Rhabditida: Heterorhabditidae), a new entomopathogenic nematode from South Africa

CITATION: Malan, A. P. et al. 2008. Heterorhabditis safricana n. sp. (Rhabditida: Heterorhabditidae) : a new entomopathogenic nematode from South Africa. Nematology, 10(3):381-396, doi:10.1163/156854108783900258.

Steinernema yirgalemense n. sp. (Rhabditida: Steinernematidae) from Ethiopia

Summary – Steinernema yirgalemense, a new species based on morphological and molecular data, is described from Yirgalem, Ethiopia. This nematode belongs to the ‘bicornutum-group’ which includes nematodes with horn-like structures in the labial region of the infective juvenile. The new species can be recognised by the infective juvenile having a body length of 635 (578-693) µm, distance from anterior and to excretory pore of 51 (45-59) µm; tail length of 62 (57-67) µm and E% (EP/tail length × 100) of 83 (67-90). The lateral field pattern is variable from anterior to posterior; the formula for the arrangement of ridges from head to tail being: 2, 6, 8, 6, 2. The new species can be further recognised by male characters: spicule with large velum and tapering posteriorly to a point, the ratio SW (spicule length/cloacal body diameter) and GS (gubernaculum length/spicule length) and especially by the presence of 12 pairs of genital papillae plus a single midventral papilla. The 12 th pair, located at the edge of the cloacal aperture, is an important character. The presence of a low epiptygma is another diagnostic character of the new species. The new species is a sister taxon to S. abbasi and is characterised by the sequence length of the ITS regions (960 bp), ITS1 (270 bp), ITS2 (284 bp) and also by the pairwise distance of both ITS and D2/D3 regions between species of nematodes in the ‘bicornutum-group’.

Heterorhabditis mexicana n. sp. (Rhabditida: Heterorhabditidae) from Tamaulipas, Mexico, and morphological studies of the bursa of Heterorhabditis spp.

Summary – A new species of nematode in the genus Heterorhabditis was found in the northern part of the state of Tamaulipas, Mexico. Morphological and molecular data indicate that this nematode is a new species. The new species is described as Heterorhabditis mexicana n. sp. and is a sister taxon to H. indica. Heterorhabditis mexicana n. sp. is morphologically similar to H. bacteriophora, H. brevicaudis and H. indica and can be distinguished from these species mainly by male and female characters. Of the examined specimens of H. mexicana n. sp., 70% of males have eight pairs of bursal papillae, compared to nine in all other species. The ratio of the gubernaculum to spicule length (GS ratio) is higher than that of H. bacteriophora, H. brevicaudis and H. indica and the length of the spicule relative to anal body width (SW) is lower than all other species. For females, the vulval form of the new species is quite different from that of those species with a similar morphology (i.e., H. bacteriophora and H. indica) and more closely resembles that of H. zealandica. The new species can also be distinguished from H. megidis, H. zealandica and H. marelatus by the body length, pharynx length of the infective juvenile and D% (distance from anterior end/pharynx length ×100), GS and SW ratios of males. In the ITS region of the rDNA tandem repeating unit, H. mexicana n. sp. has evolved 13 autapomorphic nucleotide character states, differing from its sister taxon H. indica at 113 aligned positions. The morphological and molecular data are sufficient to identify cladogenesis and delimit H. mexicana n. sp. as evolving independently from the other members of the genus.

Molecular and morphological consilience in the characterisation and delimitation of five nematode species from Florida belonging to the Xiphinema americanum -group

Taxonomic keys and original descriptions were used to identify 26 Xiphinema americanum-group populations from Florida comprising X. georgianum (eight populations), X. citricolum (six), X. floridae (six), X. laevistriatum (five) and X. tarjanense (one). Principal component analysis of a subset of 19 morphometric characters accorded with the species designations; discriminant analysis of six characters assigned 93% (111 of 119) of the specimens to the correct putative species. A phylogeny of these populations estimated from analyses of rDNA sequences (ITS and D2D3) was also congruent with species designations from taxonomic keys and PCA. The D2D3 sequences revealed very little intraspecific variation whereas each population sampled produced a unique ITS sequence. Intraspecific variation in the suites of character code values from polytomous keys resulted mainly from minor discrepancies between population character means and reported character ranges for the species. We show that, for these taxa, species delimitation based on the requirement that sister taxa evolve autapomorphies distinguishes intraspecific variation from phylogeny and, as applied to molecular characters, delimits the same taxa as those predicted by morphological keys and PCA.

FIELD EFFICACY OF TWO COMMERCIAL PREPARATIONS OF ENTOMOPATHOGENIC NEMATODES AGAINST LARVAE OF DIAPREPES ABBREVIATUS (COLEOPTERA: CURCULIONIDAE) IN ALFISOL TYPE SOIL

Abstract Spring and fall field trials were conducted to determine the efficacy of two species of entomopathogenic nematodes for the control of larvae of Diaprepes abbreviatus in a citrus grove with alfisol type soil (sandy clay loam). Both Steinernema riobrave (Bio Vector 355) as a water-dispersible granule and Heterorhabditis indica (Grubstake™ 100) as a paste on sponge at rates from 22-108 IJ’s/cm2 failed to reduce larval populations in the tree rhizosphere at 25 d post-treatment. Larval parasitism by entomopathogenic nematodes in baited screen cages was sporadic over time, with the only significant treatment effect occurring at the highest rate (108 IJ’s/cm2) of S. riobrave in the fall at 7 d post-treatment. Possible constraints to nematode efficacy are discussed.