			Home About us Contact

Infective Juveniles (infective + juvenile)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Pressure plate studies to determine how moisture affects access of bacterial-feeding nematodes to food in soil

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2002
G.W. Yeates
Summary Nematode activity in the soil depends on the presence of free water. We conducted pressure plate experiments to understand better how soil matric potential and structural degradation affect the population growth of three bacterial-feeding nematodes (Cephalobus, Pristionchus, Rhabditis). We took undisturbed cores from six soils (sand, silt loam and silty clay loam with four management regimes), and removed all fauna from them. Ten or 30 nematodes were added, and pressures corresponding to soil matric potentials of ,10, ,33, ,50, ,100 or ,1500 kPa were applied for 35 days. The nematodes were then counted. Significant reproduction of all bacterial-feeding nematodes occurred when the diameters of water-filled pores were approximately 1 ,m. This confirms observations using repacked soils and field manipulations. Only for Pristionchus did declining populations match the reduction in total soil porosity related to intensification of land use on the silty clay loam. We had not expected Cephalobus to have the fastest increase in population of the three nematodes in intact soil cores, and our evidence questions the relative importance given to the three nematode families in soil processes. The differing rates of population increase of the three nematodes in the various soils reflect both habitable pore space and trophic interactions. This suggests that the very diversity of nematode assemblages is crucial in the resilience of biological soil processes. That water-filled pores as small as 1 ,m provide suitable spaces for sizeable populations of bacterial-feeding nematodes accords with the observed migration of infective juveniles of trichostrongylid nematodes and mermithids in water films on herbage. Our results imply that assessment of the role of nematodes in soil processes may be a key to the understanding of biological interactions in water films, and the selection pressures on nematode morphology. [source]

EFFECTS OF APPLICATION PARAMETERS AND ADJUVANTS ON THE FOLIAR SURVIVAL AND PERSISTENCE OF ENTOMOPATHOGENIC NEMATODE STEINERNEMA CARPOCAPSAE ALL STRAIN ON CABBAGES

INSECT SCIENCE, Issue 2 2004
Yong-ling Jin
Abstract, Effects of the critical parameters (spray pressure, the distance between a sprayer and the sprayed plant, the concentration of infective juveniles (Us), volumes of the sprayed suspension of IJs, the temperature and humidity combinations) and the addition of various adjuvants on the survival and persistence of entomopathogenic nematode Steinernema carpocapsae All strain on leaf surfaces of the Chinese cabbage Brassica pekingensis were determined. The results showed that (1) The pressure of a sprayer had negative influence on the persistence of IJs on the leaf. (2) The numbers of the living IJs collected on the leaf significantly increased with the IJ dosages applied on the leaf when the dosage was over 2 000 IJs per mL. (3) More IJs (from 10.1 IJs/cm2 to 45.5 IJs/cm2) were collected on the leaf when more volumes of IJ suspension (from 3.3 mL to 19.8 mL) were sprayed. However, when the highest volume of IJ suspension was used, the IJ numbers collected did not increase. (4) In general, the survival of the IJs on the leaf decreased with the exposure time. (5) The formulation of IJs by adding xanthan gum, a sticker and detergent surfactant enhanced the survival and persistence of IJs. The number of living IJs on the leaf with 0.3 % of xanthan gum was 150 times higher than that of the IJs with water alone. IJ suspensions with different concentrations of glycerin and with 0.5 % molasses and 0.01 % detergent surfactant showed similar effects. [source]

Molecular detection of predation by soil micro-arthropods on nematodes

MOLECULAR ECOLOGY, Issue 7 2006
D. S. READ
Abstract The relative importance of the factors driving change in the population dynamics of nematodes in the soil is almost completely unknown. Top-down control by micro-arthropod predators may have a significant impact on nematode population dynamics. We report experiments showing that mites and Collembola were capable of reducing nematode numbers in the laboratory and were feeding on a targeted nematode species in the field. A PCR-based approach was developed for the detection of predation on three species of slug- and insect-pathogenic nematodes: Phasmarhabditis hermaphrodita, Heterorhabditis megidis and Steinernema feltiae. The collembolan Folsomia candida and the mesostigmatid mite Stratiolaelaps miles were employed as model predators to calibrate post-ingestion prey DNA detection times. Fragments of cytochrome oxidase I (COI) mtDNA were sequenced and species-specific primers were designed, amplifying 154-, 154- and 203-bp fragments for each of the nematode species. Detection times for nematode DNA within the guts of Collembola were longer than in mites, with half-lives (50% of samples testing positive) of 08.75 h and 05.03 h, respectively. F. candida significantly reduced numbers of the nematode H. megidis, with rates of predation of ,0.4 nematode infective juveniles per collembolan per hour over 10 h. Four taxa of field-caught micro-arthropod that had been exposed to the nematode P. hermaphrodita for a period of 12 h were analysed and significant numbers of three taxa tested positive. This is the first application of PCR techniques for the study of nematophagy and the first time these techniques have been used to measure predation on nematodes in the field. [source]

Scaleable downstream recovery of nematodes used as biopesticides

BIOTECHNOLOGY & BIOENGINEERING, Issue 6 2001
J.A. Wilson
Abstract This study assesses the suitability of sieving as a scaleable technique for the separation of adult nematodes from infective juveniles, the latter is an effective bioinsecticide whereas the former is waste material resulting from the fermentation process. Batch and semibatch experiments using conventional flow-assisted wet sieving and a novel cross-flow sieving technique were used to study the separation of juveniles from adult nematodes. The experiments were carried out using small-scale devices and the data were analyzed in terms of the screen effectiveness factor. The results were used to identify the sieve size and operating conditions for optimum juvenile recovery. It was found that, for a given species of nematode, optimum recovery was achieved when sieving was carried out in the cross-flow mode, the maximum recovery being a function of the size of the screen. Industrial-scale self-cleaning equipment capable of large-scale continuous screening was used to confirm the capacity of the small-scale operation for scale-up. Experimental results with this unit showed that in continuous operation sieving time is an additional parameter that influences separation performance. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 75: 733,740, 2001. [source]