Quantifying the contribution of free-living nematodes to nitrogen mineralization

Soil fauna are estimated to contribute to approximately 30 % of nitrogen mineralization (Verhoef ∧ Brussaard, 1990). Soil nematodes are important contributors to this process through their key trophic positions as microbial grazers. Quantification of this contribution has mostly relied on theoretical food web analyses (Hunt et al., 1987) or laboratory incubations with simplified and artificially constructed ecosystems (Ferris et al., 1998). Incubations are often performed on homogenized soil, though soil biota is known to be responsive to physical disturbance. Furthermore, sterilization typically relies on methods disruptive of soil structure (e.g. autoclaving, freezing). The aim of this experiment was to quantify the contribution of nematodes to nitrogen mineralization during incubation. Intact cores with a representative pore structure and entire nematode populations instead of single species were used. Gamma irradiation was selected as a sterilization method to remove only soil fauna, leaving the microflora and soil structure largely intact (McNamara et al., 2003)

Effects of selected insecticides on osmotically treated entomopathogenic nematodes

Combining environmentally friendly insecticides with entomopathogenic nematodes may constitute an effective alternative to conventional chemical control of many insect pests. The objective of this laboratory study was to evaluate the effects of selected insecticides which are commonly used for pest control in vegetables in China on osmotically treated and untreated infective juveniles of Steinernema carpocapsae strain All. The insecticides azadirachtin, chlorpyrifos, cypermethrin, fipronil, imidacloprid, malathion, thiamethoxam and chlorantraniliprole-thiamethoxam had no adverse effects on nematode survival and infectivity. In contrast, bisultap, emamectin benzoate, phoxim and rotenone proved harmful to S. carpocapsae All mainly by reducing infectivity of the infective juveniles to larvae of the greater wax moth, Galleria mellonella. Osmotic induction is a promising way to induce entomopathogenic nematodes into partial anhydrobiosis and thus increase environmental stress tolerance of the nematodes as well as their shelf life after production. The present results showed that osmotic treatment did not adversely affect fitness of the nematode in terms of its susceptibility to insecticides and even increased its tolerance to chlorpyrifos and rotenone. The results of this laboratory study indicate that several of the tested insecticides can be safely combined with S. carpocapsae All within an integrated pest management approach

A new entomopathogenic nematode species for Turkey, Heterorhabditis megidis Poinar, Jackson & Klein 1987 (Rhabditida: Heterorhabditidae)

During a survey on the occurrence of entomopathogenic nematodes (EPNs) in the Eastern Black Sea region of Turkey, a heterorhabditid species was isolated using the Galleria-baiting technique. Based on morphology and morphometrics, the isolate was identified as Heterorhabditis megidis. Sequences of the ITS region of its rDNA confirmed this identification. The species is recorded for the first time from Turkey. A more intensive survey to determine the distribution of this species, covering all parts of the Black Sea region of Turkey, is currently underway

Heat tolerance among different strains of the entomopathogenic nematode Heterorhabditis bacteriophora

Quality of biological control products based on entomopathogenic nematodes can be severely damaged due to exposure to high temperature surpassing 40A degrees C. The study screened 36 natural populations and 18 hybrid or inbred strains of Heterorhabditis bacteriophora for their response to high temperature. Nematodes were tested with or without prior adaptation to heat at 35A degrees C for 3 h. Five strains of H. indica and one of H. megidis were also included. Molecular identification using nuclear ribosomal DNA sequences confirmed the designation to the three Heterorhabditis spp. The mean tolerated temperature ranged from 33.3A degrees C to 40.1A degrees C for non-adapted and from 34.8A degrees C to 39.2A degrees C for adapted strain populations. H. indica was the most tolerant, followed by H. bacteriophora and H. megidis. No correlation was recorded between tolerance assessed with and without adaptation to heat, implying that different genes are involved. Correlation between heat tolerance and mean annual temperature at place of origin of the strains was weak. A high variability in tolerance among strains and the relatively high heritability (hA(2)A = 0.68) for the adapted heat tolerance recorded for H. bacteriophora provide an excellent foundation for future selective breeding with the objective to enhance heat tolerance of H. bacteriophora

Characterisation of a population of Pratylenchus hippeastri from bromeliads and description of two related new species, P. floridensis n. sp. and P. parafloridensis n. sp. from grasses in Florida

Morphological and molecular analyses confirmed the presence of P. hippeastri in regulatory samples collected in commercial bromeliad operations from genera Guzmania, Neoregelia and Vriesea in central and south Florida, USA. These P. hippeastri from bromeliads contained males which were not detected in the type population from amaryllis. The rDNA sequences of these males matched those of P. hippeastri female type material. Pratylenchus hippeastri and related root-lesion nematodes from several hosts in Florida were characterized at the morphological and molecular level, whereas other samples from Russia and South Africa at the molecular level only. Phylogenetic and sequence analysis using the ITS rRNA gene of these root-lesion nematodes revealed the presence of eight putative new species (spH1-H8) closely related to P. hippeastri. However, detailed morphological and molecular analyses are still required to confirm their unique species status. Here we describe two Florida representatives of the amphimictic root-lesion nematodes from Bahia grass (N1) and maidencane (N2), previously characterized by Inserra et al. (1996) and Duncan et al. (1999), as two new species phylogentically related to P. hippeastri and named Pratylenchus floridensis n. sp. and P. parafloridensis n. sp., respectively. The small round or oval, rarely rectangular and occasionally oblong and enlarged spermatheca and the bluntly pointed or subacute tail with smooth and occasionally indented terminus separate P. floridensis n. sp. from P. parafloridensis n. sp., which has a quadrangular spermatheca and a sub hemispherical or bluntly pointed tail with generally smooth and rarely indented terminus. However, these characters may overlap in some specimens making the morphological separation problematic without the use of molecular analysis. The close phylogenetic relationships shared by the species characterized in this study indicate that they are representatives of a P. hippeastri species complex

Vertical distribution of the plant-parasitic nematode, Meloidogyne chitwoodi, under field crops

The root-knot nematode Meloidogyne chitwoodi is a severe pest on sandy soils in Belgium and causes quality damage to economically important crops such as carrot, potato and black salsify. Pre-planting soil sampling to detect infestations has proven useful to farmers when taking decisions on the crop rotation. To develop an adequate sampling strategy, the vertical distribution of M. chitwoodi was examined under summer barley, carrot, fodder beet, bean, marigold and black fallow on two fields with a sandy soil. Soil samples were collected at monthly intervals from April 2004 to April 2006. Cores were taken to a depth of 70 cm and split into 10 cm segments. Nematodes were extracted by zonal centrifugation. Fodder beet increased the population of M. chitwoodi immensely; carrot was also a good host. Barley was a moderate host and under bean and marigolds the population decreased. The relative distribution of M. chitwoodi over the different soil layers during two successive years was consistent in each field. The different successions with good, moderate and poor hosts did not influence this distribution significantly. A logistic model was fitted to the mean cumulative percentages of nematodes at increasing soil depth. Farmers are advised to take soil samples for detection of M. chitwoodi immediately after harvest, especially after crops with a long field period. Adapting the depth of the cores taken to the vertical distribution of the population can increase the chances of detection. Our results suggest that this distribution is persistent in crop rotations and depends on field characteristics