Saprophagous Nematodes Research Articles

Scavenging behavior and interspecific competition decrease offspring fitness of the entomopathogenic nematode Steinernema feltiae.

Entomopathogenic nematodes (EPNs) are well-studied biocontrol agents of soil-dwelling arthropod pests. The insecticidal efficiency of EPNs is modulated by food web dynamics. EPNs can reproduce in freeze-killed insect larvae, even in competition with free-living bacterivorous nematodes (FLBNs) in the genus Oscheius. The objective of this study was to assess the efficiency of EPNs as scavengers when competing with free-living saprophagous nematodes and fungi, and to determine the possible impact on subsequent EPN offspring fitness. Live and freeze-killed larvae of Galleria mellonella were used to evaluate the reproduction rate and progeny fitness of two EPN species, Heterorhabditis bacteriophora and Steinernema feltiae, applied individually or combined with the FLBN species Oscheius onirici or Pristionchus maupasi, or Aspergillus flavus, an opportunistic saprophytic fungus. We hypothesized that (1) EPN scavenging behaviors previously observed (for H. megidis and S. kraussei) apply to other EPN species, (2) infective juveniles (IJs) emerging from freeze-killed larvae will display reduced pathogenicity and reproduction, and (3) fitness reduction will be amplified by exposure to other organisms competing for the resources. The reproduction rate of S. feltiae was lower in freeze-killed larvae than in larvae infected and killed by the nematode, whereas H. bacteriophora failed to reproduce as a scavenger. The S. feltiae F1 IJs that emerged from freeze-killed larvae exhibited lower pathogenicity rates than IJs resulting from entomopathogenic activity, and also lower reproductive rates if they experienced high FLBN competitive pressure during development. This study illustrates that scavenging is a suboptimal alternative pathway for EPNs, especially in the face of scavenger competition, even though it provides a means for some EPN species to complete their life-cycle.

Fatal Parasitic Meningoencephalomyelitis Caused ByHalicephalobus deletrix: A Case Report and Review of the Literature

Infection with the saprophagous nematode Halicephalobus species is uncommon but has been reported in horses worldwide. Only 3 human cases have been previously described, all of which have been fatal. We report a fourth fatal case, which occurred in a 39-year-old woman who presented with meningeal signs, altered mental status, and a prodromal pruritic rash. Diagnostic evaluation included an open brain biopsy, which was diagnosed as granulomatous vasculitis. The patient subsequently died after a course of steroids and cyclophosphamide. At autopsy, a robust perivascular mixed inflammatory infiltration of the brain parenchyma, meninges, and ventricular system was present with larval forms and mature nematodes morphologically consistent with Halicephalobus deletrix . Although extremely rare, this organism needs to be considered in the differential diagnosis of human helminthic infection of the central nervous system.

Fatal parasitic meningoencephalomyelitis caused by Halicephalobus deletrix : a case report and review of the literature.

Infection with the saprophagous nematode Halicephalobus species is uncommon but has been reported in horses worldwide. Only 3 human cases have been previously described, all of which have been fatal. We report a fourth fatal case, which occurred in a 39-year-old woman who presented with meningeal signs, altered mental status, and a prodromal pruritic rash. Diagnostic evaluation included an open brain biopsy, which was diagnosed as granulomatous vasculitis. The patient subsequently died after a course of steroids and cyclophosphamide. At autopsy, a robust perivascular mixed inflammatory infiltration of the brain parenchyma, meninges, and ventricular system was present with larval forms and mature nematodes morphologically consistent with Halicephalobus deletrix . Although extremely rare, this organism needs to be considered in the differential diagnosis of human helminthic infection of the central nervous system.

Use of crop residues for the control of Meloidogyne incognita under laboratory conditions

This laboratory study evaluates the biofumigant effect of different organic materials with the aim of developing non-chemical alternatives for the management of Meloidogyne incognita (Kofoid & White) Chitwood populations. Sources of organic material from the production system were selected with the aim of reducing agricultural residue accumulation problems as well as decreasing the costs due to the use of chemical fertilizers and pesticides. The selected materials were residues from pepper, strawberry, tomato and cucumber crops, orange juice industry residues, commercial manure and sheep manure, applied at different dosages. Two biofumigation assays were performed under laboratory conditions, using alkaline soils from the Torreblanca area (Murcia, Spain) and acidic soils from the Villa del Prado area (Madrid, Spain). The assays evaluated the effect of the treatments on M. incognita juveniles and other soil organisms, the nematode galling index on tomato roots (susceptible cv. Marmande) grown in the biofumigated soil and soil fertility parameters. The results showed that all biofumigant materials significantly decreased M. incognita populations and galling indices in tomato cv. Marmande. A greater effect was observed on galling indices when applying crop residues together with manure than with the residues alone. Biofumigation had a general beneficial effect on soil fertility, generally increasing nitrogen, organic carbon, pH and potassium levels, and also calcium levels when crop residues of pepper and strawberry were applied. There were no important variations in the number of saprophagous nematodes, dorylaimids and enchytraeids.

The efficacy of nematophagous fungi on predaceous nematodes in soil compared with saprophagous nematodes in mushroom compost

The predaceous efficacy of five nematophagous fungi was investigated against the predaceous soil nematode, Butlerius sp., and the saprophagous nematode, Panagrolaimus sp., during the cultivation of the commercial mushroom, Agaricus bisporus. Two isolates, Arthrobotrys oligaspora and Dactylaria scaphoides, produced three dimensional adhesive networks in the isolation of other predatory organs, while Dactylaria dasguptae, an unidentified Dactylella species and the egg-parasitizing fungus, Dactylella oviparasitica, produced both networks and detachable knobs in the presence of nematodes under our experimental conditions. Preliminary studies in soil microhabitats proved A. oligospora and the unidentified Dacylalla species to be potentially effective biological control agents, immobilizing 80% of the total nematode population. However, during the cultivation of A. bisporus, the most biologically effective fungus, Dactylaria dasguptae, reduced the nemtode population by 35%. There is some evidence to suggest that saprophytic nematophagous fungi would make effective biocontrol agents.

Cultural Studies On Soil Nematodes and Their Fungal Hosts

In laboratory experiments survival, feeding and reproduction of nematodes in cultures with mycorrhizal and saprophytic fungi were investigated. Nematodes extracted from the organic layer of a spruce forest soil were inoculated to fungal plates. The fungal feeder Aphelenchoides saprophilus was the most successful species to multiply. With mycorrhizal fungi as a food source its population developed faster and to a greater extent than it did with saprophytic fungal species. The grazing of A. saprophilus reduced mycelial weight and fungal growth rate. Similar effects are likely to occur in the field, and can influence mycorrhizal development or affect competition between soil fungi. Besides A. saprophilus, the saprophagous nematode Acrobeloides nanus reproduced well in cultures with mycorrhizal fungi. There may be an element of substrate ingestion or grazing on fungal hyphae for some bacterial feeding nematodes.

Effects of free-air CO2 enrichment on microbial populations in the rhizosphere and phyllosphere of cotton

Cotton (Gossypium hirsutum L.) plants were exposed to free-air CO2 enriched (FACE = 550 μmol mol−1) or ambient (CONTROL = 370 μmol mol−1) levels of atmospheric CO2 and to wet (100% of evapotranspiration replaced) or dry (67% of ET replaced) soil water content treatments. Foliar, soil and root samples were collected in June and August 1991 to determine the effects of elevated CO2 on selected groups of phyllosphere and rhizosphere microorganisms. Foliage and rhizosphere soil were analyzed for bacteria and/or fungi using dilution plating. Mycorrhizal colonization of cotton roots was assessed. Root-zone soil was analyzed for populations of nematodes, microarthropods and Rhizoctonia using various extraction methods. A dehydrogenase assay for total microbial respiration and a bioassay for cotton root infecting organisms were also conducted using root-zone soil. Populations of fungi on cotton leaves varied, by genera, in response to CO2 enrichment, but none was affected by soil water content treatments; populations of foliar bacteria were not affected by either CO2 or soil water content treatments. In August, higher total numbers of rhizosphere fungi were found under the wet compared with the dry soil water treatment, but differences related to CO2 were not detected. There was a trend for infestation by Rhizoctonia solani to be higher under FACE in the August sample, but the soil bioassay demonstrated no increase in damping-off potential. There was a significant interaction between CO2 concentration and soil water content for populations of saprophagous nematodes; populations were different between the CO2 levels in the dry soil treatment only, with higher numbers under FACE. Microarthropod numbers were low; however, there was a trend for Collembola populations to be higher under FACE in the August sample and more fungi were isolated from Collembola in June. Total microbial activity was higher under FACE at both sample dates. Effects of elevated atmospheric CO2 on plant microbe interactions could have profound influence on the productivity of agro-ecosystems, and deserve further research.

Evaluation of powdered pine bark for control ofMeloidogyne arenaria andHeterodera glycines on soybean

Commercially avaiable pine bark nuggets (composted) and fresh pine bark were ground into powders and added at rates of 0 to 50 g kg−1 to field soil infested withMeloidogyne arenaria andHeterodera glycines. The treated soil was maintained moist in the greenhouse for 2 weeks, sampled, and planted with ‘Davis’ soybean (Glycine max.). Eight weeks after planting, numbers ofM. arenaria andH. glycines in soil decreased with increasing amounts of composted or fresh pine bark. No juveniles were present in soil treated with 5% pine bark. The number of galls and cysts g−1 root decreased in proportion to the amount of pine bark added to soil. Gall and cyst formation was completely eliminated at the 5% rate. Numbers of saprophagous nematodes were highest in soil with 4–5% pine bark. The activity of several soil enzymes was correlated with the addition of both composted and fresh pine bark. Fresh pine bark powder caused an increase in soil enzyme activity compared to composted pine bark, but did not provide consistent control of gall and cyst formation.

Analysis of the Predation By Aporcelaimellus Nivalis On Prey Nematodes From Different Prey Trophic Categories

Numerical analysis of the predatory behaviour of Aporcelaimellus nivalis, including strike rate encounters resulting in attack, attacks resulting in wounding, feeding after wounding, prey left unconsumed and duration of feeding upon an individual, was made in relation to five different prey trophic categories: 1) Bacterial feeders (Saprophagous nematodes), 2) Migratory juveniles (Sedentory endoparasitic nematodes), 3) Epidermal feeders (Ectoparasitic nematodes), 4) Cortical feeders (Ectoparasitic nematodes) and 5) Predatory nematodes. The degree of susceptibility on individual prey and prey trophic categories as a whole was found to vary. The endoparasitic nematodes were highly susceptible (prey susceptibility = 77%) but predators resisted predation well (prey resistance (PR) = 78%). Characteristics such as thick body cuticle, body annulations and thick longitudinal cuticular folds provided physical resistance to Hoplolaimus indicus, Scutellonema sp., Hemicriconemoides mangiferae, Hemicycliophora dhirendri and Mononchoides fortidens (PF= 100%). Mononchus aquaticus and Rhabditis sp. exhibited behavioural resistance in the form of rapid undula. tory movements and took evasive action when attacked. No individuals of Helicotylenchus indicu. were consumed by the predators. This was attributed to unfavourable/toxic prey contents (chemical resistance). Duration of feeding on an individual prey depended on the size of the prey and other physical and chemical factors.

Effects of bacteria isolated from a saprophagous rhabditid nematodeCaenorhabditis eleganson the mycelial growth ofAgaricus bisporus

P. S. GREWAL AND P. HAND. 1992. The effects of 10 species of bacteria isolated from a saprophagous rhabditid nematode Caenorhabditis elegans on mycelial growth of the cultivated mushroom Agaricus bisporus were studied in agar cultures. Bacterial species showed differential effects on the mycelial growth of A. bisporus and the effects also depended upon the mushroom strain (C43, C54 and U3). Bacillus cereus, Bacillus sp. and Enterobacter amnigenus caused significant inhibition in mycelial growth of all three strains of A. bisporus. Pseudomonas aeruginosa, Ps. fluorescens biovar reactans and Ps. maltophilia resulted in a significant increase in mycelial growth of C54 strain. Enterobacter cloacae caused a mean inhibition of about 83% in the linear mycelial extension of the most commonly cultivated mushroom strain U3. Bacillus cereus, Ent. amnigenus and Ent. cloacae produced volatile inhibitory substance(s). This is believed to be the first report about the inhibitory effects of specific bacteria isolated from a saprophagous nematode on the mycelial growth of A. bisporus.

Food dependence and energetics of freeliving nematodes : I. Respiration, growth and reproduction of Caenorhabditis briggsae (Nematoda) at different levels of food supply.

Some bioenergetic parameters of Caenorhabditis briggsae, a saprophagous nematode, were analysed under different conditions of food availability. Respiration (R) and production rates (P) of experimental animals grown on media of defined bacterial concentrations were measured throughout the life cycle of the species at 20°C. Energetics are expressed in the form of instantaneous rates and as cumulative budgets. 1. Food dependence: The food threshold of the species is defined as A (assimilation)=R, P=zero. The respiratory level of the species is generally high compared to other nematode species and increases only weakly with food availability. Starvation (food densities below threshold) is expressed in a strong reduction in metabolism within 48 h. The food dependence of biosynthetic processes (body growth and egg production) follows a hyperbolic form, which can be described by the Michaelis-Menten function. The relationship P:R changes drastically with availability of food, e.g. the production efficiency for the period of maximal reproduction is 0% at 2·108 cells ml-1 (threshold) and 86% at 1010 cells ml-1. 2. R and P follow different forms of size dependence in the course of the life cycle. The relationship between R and body weight (W) can be described by an allometric function, e.g. at high food density, R=2.8 W 0.75 (R in nl O2 ind-1 h-1; W in μg fresh weight). Weight-specific production rates vary considerably during the life cycle: ±constant in the early larval phase (exponential growth, "g"=1.44 day-1 at 1010 cells ml-1); decreasing in the latter larval phase; peak values shortly after onset of reproduction as a result of both body growth and egg production. 3. Differences in resource allocation at varying food densities are also manifest in cumulative energy budgets, e.g. higher R cum is necessary to achieve the same body size at lower food densities. Size at maturation and egg size are reduced to a different degree at low food densities, indicating bioenergetical constraint and trade-off between metabolic processes.

Responses of Plant Parasitic and Saprophytic Nematode Populations to Composted Municipal Refuse

AbstractThe effective disposal of composted municipal refuse poses important ecological problems. Efforts to recycle this material must be guided by knowledge of its ecological impact upon a natural environment. The influence on nematode populations of incorporating composted municipal refuse in Leon fine sand was investigated over a period of 2 years. This study was a randomized complete block experiment with oat (Avena sativa L.) and sorghum (Sorghum bicolor L. Moench) used as test crops. Mineral fertilizer (10‐4.4‐8.3) applied at the rate of 0.9 tons/ha was compared with compost applied at rates of 1, 2, 4, 8, 16, or 32 tons/ha. Populations of Helicotylenchus spp., plant parasitic nematodes, were highest in the fertilized and lowest in the 8, 16, and 32 tons/ha compost plots. Populations of another parasitic nematode, Criconemoides spp., were not greatly reduced by compost. Populations of cephalobids and rhabditids (saprophagous nematodes) were highest in the soil receiving 32 tons/ha of compost.

Cylindrocorpus nom. nov. for Cylindrogaster Goodey, 1927 (Nematoda)

Perusal of the first volume of “Nomenclator Zoologicus” shows, on p. 927, that the generic name Cylindrogaster was first proposed by Stål in 1855 for a Dermapteran insect. As a consequence of this it becomes necessary to put forward a new generic name in place of Cylindrogaster which the writer (Goodey, 1927) gave to a saprophagous nematode obtained from a culture of rat faeces.