Nematode Migration Research Articles

Enhanced Trehalose Accumulation and Desiccation Survival of Entomopathogenic Nematodes Through Cold Preacclimation

Limited storage stability is a major obstacle to further expansion of the use of entomopathogenic nematodes for pest control. Progress has been made that Steinernema carpocapsae can now be stored under partial anhydrobiosis for up to 6 months at 25°C and 10 months at 5°C in a water-dispersible granular (WG) formulation. However, other species have been more difficult to store in the WG formulation due to migration of nematodes out of the granules and sensitivity of some species to desiccation directly at cold temperatures. As acclimation to cold induces trehalose accumulation (a major cryo- and desiccation protectant) in many invertebrates, it was hypothesized that cold preacclimation of entomopathogenic nematodes will enhance their survival in the WG formulation at cold temperatures. This hypothesis was tested using a temperate species Steinernema feltiae , a subtropical species S. carpocapsae , and a tropical species Steinernema riobrave possessing different thermal niche breadths and reproduction temperature optima. Cold acclimation of infective juveniles increased trehalose accumulation in all three species and the amount of trehalose accumulated was both temperature and species dependent. Trehalose content reached at its peak after 6 days at 5°C in S. feltiae (82.28 w g/mg dry weight), after 10 days at 10°C in S. carpocapsae (94.16 w g/mg dry weight) and after 6 days at 15°C in S. riobrave (47.58 w g/mg dry weight). Cold preacclimation at 5°C for 2 days enhanced desiccation survival of S. feltiae in 25% glycerol (osmotic desiccation) at both 5 and 25° and of S. carpocapsae and S. riobrave only at 5°C. Non-cold acclimated S. carpocapsae and S. riobrave were extremely sensitive to desiccation directly at 5°C in 25% glycerol, resulting in over 98% mortality within 6 days, but S. feltiae was more sensitive to desiccation at 25°C than at 5°C. Cold preacclimation increased survival of all the three species in the WG formulation at both 5 and 25°C. The survival of S. riobrave at 5°C in the WG formulation was positively correlated with the length of preacclimation period at 5°C (R 2 = 0.99) and with the amount of trehalose accumulated during cold preacclimation (R 2 = 0.81). These results support the hypothesis that cold preacclimation enhances desiccation survival of entomopathogenic nematodes at cold temperatures and the increased survival correlates well with the increased trehalose accumulation. Results also demonstrate that cold preacclimation can be used as a tool to enhance survival of nematodes in the formulations with reduced water activity.

Automated technology for in vivo mass production of entomopathogenic nematodes

As the only biocontrol agent available for many soil insects, entomopathogenic nematodes should be poised for wider use, as regulatory scrutiny in the USA continues to restrict or ban important chemical insecticides. One component of nematode production in the USA is a cottage industry of low volume producers using in vivo technology, based on a method devised in 1927: the White trap. We report the first scalable system for in vivo nematode mass production. Unlike the White trap, there is no requirement for nematode migration to a water reservoir. The LOTEK system of tools and procedures provides process technology for low-cost, high-efficiency mass production. The system consists of: (1) perforated holding trays to secure insect hosts during inoculation, conditioning (synchronizing nematode emergence), and harvesting, (2) an automated, self-cleaning harvester with misting nozzles that trigger infective juvenile emergence and rinse the nematodes through the holding trays to a central bulk storage tank, and (3) a continuous deflection separator for washing and concentrating nematodes. The harvester collects 97% of Heterorhabditis bacteriophora Poinar that emerged from Galleria mellonella (L.) cadavers in 48 h. The separator removes 97.5% of the wastewater in three passes, while nematode concentration increased 81-fold. The rearing system offers an increase in efficiency relative to the conventional White trap method with reduced labor and space.

A MATHEMATICAL ANALYSIS OF A MINIMAL MODEL OF NEMATODE MIGRATION IN SOIL

A minimal model of nematode migration through soil in response to a chemical gradient is presented. We consider Fickian, fractal and porous-media type diffusion of the nematodes, for which the steady-state nematode distributions are found to compare favourably with experimental observations. Analytical results for Fickian nematode diffusion are presented, which are appropriate for the small- and large-time evolution of a nematode distribution. Numerical integrations allow us to compare the three types of nematode diffusion, to provide numerical validation of our analytical results, and to investigate the dependence of the results of our model upon certain key parameters. We conclude with a summary of results and a call for further experimental work.

Tidal migration of nematodes on an estuarine tidal flat (the Molenplaat, Schelde Estuary, SW Netherlands)

The vertical distribution patterns of the nema- tode community and of the 10 most dominant nematode spe- cies on an intertidal flat in the Schelde Estuary (the Molen- plaat, The Netherlands) are described at specific time intervals over a tidal cycle. The observed distribution profiles indicate that vertical migrations occur and are species-spe- cific. The predatory Enoploides longispiculosus and the deposit-feeding Daptonema normandicum migrated upwards at incoming tide and downwards when the flat became exposed, while another deposit feeder, Daptonema setosum, did the opposite. Several abiotic and biotic factors may con- tribute to the observed patterns. Hydrodynamics, pore water drainage and episodic steep increases in temperature upon low tide exposure as well as vertical movements of prey organisms may have been of particular relevance at the time and site of sampling. However, the impact of each of these factors needs further investigation. The present study corrob- orates the dynamic nature of vertical distribution profiles of nematodes in intertidal sediments, highlighting the impor- tance of sampling time with respect to the tide, as well as a species approach.

Early Symptom Development and Histological Changes Associated with Migration of Bursaphelenchus xylophilus in Seedling Tissues of Pinus thunbergii.

In order to clarify the mechanism of pine wilt caused by the pinewood nematode (PWN), Bursaphelenchus xylophilus, nematode migration in tissues and disease symptoms in Pinus thunbergii seedlings were investigated. One-year-old seedlings were inoculated with different pathogenic isolates of PWN under two different temperatures. At an early stage of symptom development, a virulent isolate of PWN multiplied in both bark and xylem and was distributed in cortical resin canals, cortical tissue, and xylem resin canals at 30°C. Cell death and disease symptoms developed in both bark and xylem. The virulent isolate of PWN at 25°C and the avirulent isolate of PWN at 30°C were distributed mainly in cortical resin canals, but rarely in xylem resin canals and cortical tissue. Disease symptoms and cell death occurred in cortical resin canals and rarely occurred in other tissues. These results demonstrated that the virulent isolate of PWN at low temperature and avirulent nematodes could not easily migrate to xylem resin canals and cortical tissue. It was shown that cell death and early symptom development coincided with PWN migration and, therefore, PWN invasion induces cell death and early symptom development.

Analytical solutions of a minimal model of species migration in a bounded domain

A minimal model of species migration is presented which takes the form of a parabolic equation with boundary conditions and initial data. Solutions to the differential problem are obtained that can be used to describe the small- and large-time evolution of a species distribution within a bounded domain. These expressions are compared with the results of numerical simulations and are found to be satisfactory within appropriate temporal regimes. The solutions presented can be used to describe existing observations of nematode distributions, can be used as the basis for further work on nematode migration, and may also be interpreted more generally.

Vertical migration of nematodes and soil-borne fungi to developing roots of Ammophila arenaria (L.) link after sand accretion

Ammophila arenaria benefits from regular burial of windblown beach sand as it allows escape from soil-borne pathogens (nematodes and fungi). The present study was done to obtain more insight into the timing and order of migration of the soil organisms towards the newly formed roots. Accordingly, plants were grown in non-sterilized root zone soil, buried by 20 cm of beach sand and harvested periodically during one growing season. Plants were buried in November. After 17 weeks, the internodes of the planted seedlings elongated and again 10 weeks later, in May, new roots began to develop. The majority of plant parasitic nematodes remained in the original core until root formation started in the deposited layer. Juveniles of Heterodera spp. successfully infected the roots, formed cysts and produced an offspring in October, resulting in high numbers of larvae at the end of the experiment. In February, at the first harvest of plants, fungi were isolated from soil and buried shoots in the whole deposited layer, although it was still winter. During the growing season a shift in the community of fungi in soil and buried shoots occurred in both the original core and the deposited layer. In both layers, the plant pathogenic fungi were gradually replaced by saprophytes. As all fungal and nematode species were able to colonize the deposited sand layer within one year, we conclude that both fungi and nematodes in the root zone of A. arenaria are very well adapted to sand deposition. Because of the fast migration rate of both pathogenic fungi and parasitic nematodes, the window for A. Arenaria to escape in time from its soil-borne pathogens seems to be narrow.

Dynamics of nematodes and protozoa following the experimental addition of cattle or pig slurry to soil

An experimental system was used in which slurry could be placed in the central section of a tube, between two cores of packed, sieved soil. The system simulated the direct injection of slurry into soil and there was movement of water and substrate from the slurry into the surrounding soil. The effects of initial soil moisture, soil nitrate concentration and slurry type, on communities of nematodes and protozoa in soil sections adjacent to and away from the slurry were investigated. Protozoa increased rapidly in the soil layer adjacent to the slurry, but responded more quickly following the addition of pig slurry than cattle slurry. Pig slurry also specifically stimulated ciliates, especially larger Hypotrich ciliates. Nematodes, however, were stimulated to a greater extent by cattle than pig slurry. It is argued that pig slurry contained a greater proportion of readily-available C than cattle slurry. There was also a substantial increase in nematode numbers in soil up to 12 cm from the slurry. This was attributed to the migration of nematodes away from the soil section adjacent to the slurry. A separate experiment was conducted with gel-stabilised cattle slurry, which restricted the movement of water and substrate from the slurry. In this case there was no stimulation of microfauna in soil more than 2 mm from the soil-slurry interface, the largest changes occurred within the slurry phase.

Development of a serum plate agglutination test to detect antibodies to Ornithobacterium rhinotracheale.

sistent with Elaeophora, a diagnosis of elaeophorosis, probably caused by E. schneideri, was made. Blindness, circling, and ataxia as seen in this moose are characteristic clinical signs of infection with E. schneideri in moose from Montana5 and Colorado.4 Histopathologic findings in moose elaeophorosis are similar to those of elk (Cervus elaphus)5 and include regions of cerebrocortical necrosis, intimal proliferation within leptomeningeal arteries, and thrombosis of cerebral vessels. The vasculitis reported in this moose has been described in elk with elaeophorosis.1 Both previous reports of elaeophorosis in moose contained descriptions of nematodes within histologic sections of brain, and nematodes were recovered from the carotid arteries.4,5 Despite examination of numerous brain sections and other tissues, only the nematode within an artery surrounding a mesenteric lymph node was observed; the carotid arteries were not examined grossly. The observation of the larval nematode within a mesenteric vessel is not surprising based on observations in elk with elaeophorosis in which parasites were observed within multiple organ systems. Postmortem migration of nematodes was also thought to occur.1 The cause of the observed eosinophilic dermatitis was not determined and although a localized reaction to circulating Elaeophora microfilariae was considered, no microfilariae were observed on histologic examination. This is the first report of elaeophorosis in a moose from Washington state and the first description of this parasite from the eastern portion of the state. The only previous report of elaeophorosis reported from Washington state was E. schneideri from a black-tailed deer (Odocoileus hemionus columbianus) from the western portion of the state.2 Although E. schneideri is considered rare in Washington,2 moose may be a sensitive indicator species for the presence of the parasite, especially in areas where the parasite has not been diagnosed previously. Acknowledgements. We thank Dr. Melinda Wilkerson, Washington Animal Disease Diagnostic Laboratory, for assistance with histopathology, Dr. Scott Lyell Gardner, University of Nebraska State Museum, for assistance in examination of the parasite, and Steve Judd, the Colville Indian Tribe, for bringing this moose to our attention.

Changes in Nematode Population and Movement in Pine Seedlings with the Development of Pine Wilt Disease : Suppressive Effect of Water Extracts from Infected Pine Seedlings on the Movement of Nematodes

Pinus thunbergii (susceptible to pine wilt) and P. taeda (resistant species) seedlings were inoculated with one of the following three Bursaphelenchus isolates; one pathogenic (B. xylophilus) and two nonpathogenic (B. xylophilus and B. mucronatus) isolates. The effect of water extracts from the nematode-inoculated seedlings on the nematodes' movement was tested in relation to the dynamic resistance induced in the host. In every water extract from seedlings of either pine species, the movement of all isolates was inhibited, however, the inhibition to pathogenic isolates diminished later on. The results indicate that some substance(s) responsible for the inhibition of nematode movement was produced in the stems of the inoculated pine seedlings. The substance was denatured as the disease progressed, and movement of the pathogenic isolate became free from inhibition, while that of two nonpathogenic isolated did not. Regardless of the nematode isolate inoculated, extracts from P. taeda were somewhat more suppressive to nematode movement than those from P. thunbergii, although the differential manner of inhibition against the three nematode isolates was similar. Nematode migration and proliferation in stems of the seedlings, decline of water content and resin exudation of the stems were confirmed only when susceptible pine seedlings were inoculated with the pathogenic isolate.

Migration of bacterial-feeding nematodes, but not protozoa, to decomposing grass residues

Populations of bacterial-feeding nematodes and protozoa developing in soil amended with dried grass powder or a nutrient solution were monitored in experimental systems designed to prevent migration from surrounding unamended soil. The addition of nutrient solution stimulated both microbial activity, as determined by dehydrogenase activity, and protozoa, but brought about no increase in nematode numbers. Amendment of soil with grass, however, caused an increase in both types of grazer, with the maximum biomass of protozoa (180 μg g-1) exceeding that of bacterial-feeding nematodes (42 μ g-1). The decomposing grass was rapidly colonised by rhaditid nematodes, mainly Caenorhabditis sp. Incubating grass-amended soil in the absence of any surrounding soil, to prevent migration, changed the microflora from predominantly bacterial to predominantly fungal, and so could not be used to compare treatments with and without migration. Surrounding the amended soil with sterilised soil prevented migration and caused no detectable change in the microflora. This treatment demonstrated that migration plays an important part in the colonisation of decomposing substrates by nematodes, but that protozoa do not migrate in soil. The nematodes migrated from a volume of unamended soil that was equivalent to eight times the volume of amended soil. The potential effects of the large grazing pressure on the subsequent decomposition of the grass residue are discussed.

The early migration of Elaphostrongylus rangiferi in goats.

The migration of nematodes of the genus Elaphostrongylus (Metastrongyloidea: Protostrongylidae) from the gut into the tissues of ruminants has not been described. Detailed histologic studies were performed on five goat kids that had received oral doses of 1,000-1,500 infective larvae of Elaphostrongylus rangiferi Mitskevich, 1960 and were subsequently autopsied at days 2, 4, 6, 10, and 14 post inoculation. The main migratory route of E. rangiferi larvae seemed to be haematogenous. The larvae penetrated the venules of the abomasum and followed the blood stream via the liver to the lungs. In the lungs, the larvae entered pulmonary venules and passed into the arterial circulation reaching the central nervous system (CNS) and other organs between days 6 and 10 post inoculation. Some of the larvae that had lodged in tissues outside the CNS probably migrated into it along the spinal nerves. A marked eosinophilia was present from day 8 post inoculation.

Bursaphelenchus xylophilus induced pine wilt: Factors associated with resistance

AbstractWe investigated factors affecting resistance of Pinus spp. to Bursaphelenchus xylophilus. Nematode migration and multiplication was inhibited in resistant P. taeda. As a consequence acceleration of monoterpene synthesis terminated, tracheid‐cavitation did not become extensive, and xylemsap ascent was not significantly blocked. In P. strobus, inhibition of nematode activity was not as complete as in P. taeda, and temporal needle‐wilting was seen on some branches. Although this suggest some blockage of xylem water conduction, we were unable to confirm development of cavitation induced by nematode activity. β‐myrcene concentration in these species was not related to resistance.

Metabolic studies on thiobiotic free-living nematodes and their symbiotic microorganisms

The marine, free-living Stilbonematinae (Nematoda: Desmodoridae) are remarkable for the ectosymbiotic, prokaryotic microorganisms that populate their entire body surface. These nematodes occur in sulfidic sediments in the microoxic zone just above the sulfide maximum. Several facts point to a chemolithotrophic, sulfide oxidizing nature of the microorganisms. The oxygen uptake of three species was measured with and without their microbial coat using Cartesian and Gradient Diver microrespirometry in February 1989 at Carrie Bow Cay (Belize Barrier Reef). Symbiont-free stilbonematids exhibited constant and uniform oxygen uptake rates over several hours; rates which are significantly lower than those of oxyphilic nematodes. Freshly extracted stilbonematids, with intact bacterial coats, consumed significantly more oxygen than symbiont-free worms in the first 3 h of measurement. While the rates of aposymbiotic worms were more or less constant over time, the rates of symbiont-carrying worms exhibited a conspicuous drop during prolonged respiration. InStilbonema sp., symbiont carrying individuals kept under oxygenated conditions for more than 12 h had a respiration rate similar to those of aposymbiotic specimens. When such worms were re-incubated in sulfide-enriched seawater the respiration rate was significantly elevated. The possibility of “recharging” the oxygenated symbiosis system via sulfide-uptake is seen as an indication that storage of reduced sulfur compounds, or reserve substances synthetized in the presence of sulfide, play a decisive role in the metabolisms of the symbiotic bacteria. Migration of nematodes between sulfidic and oxidized sediment-layers are, most likely, the key to understanding the success of this nematode-bacteria symbiosis.

The influence of autumn dewfall on spatial and temporal distribution of nematodes in the desert ecosystem

Nematodes are one of the most abundant fractions of the soil faunal biomass in deserts. Study of a single autumn dewfall event showed: rapid diurnal change in soil moisture that was evident to a depth of 30 cm; vertical migration of nematodes that correlates well with changes in soil moisture; density of nematodes under and outside of shrub canopies varied in response to moisture but distribution into trophic groups at the two sites was identical; the distribution pattern and behavior of Negev nematodes agrees well with those found in American deserts. Findings support the hypothesis that rapid response of desert nematodes to moisture is a significant survival mechanism.

A Procedure for Extracting Large Numbers of Debris-Free, Living Nematodes from Muddy Marine Sediments

Procedures commonly used for extracting nematodes from sediments do not provide sufficient quantities of living, chemically unaltered individuals required for biochemical studies. Microscopic hand-sorting and centrifugal flotation techniques either are too time-consuming or may be physically and/or chemically damaging to the organisms. A simple, time-efficient extraction procedure which modifies the Baermann funnel apparatus with a filtering layer of glass beads or sterile dune sand is described. With only three hours of technician time for set-up and harvesting, six funnels provided a combined yield of 35,000 living nematodes free of sediment and debris. The experimental study of meiofauna using biochemical techniques, such as dietary immunoassay (Feller et al., 1979) or stable isotope tracers (Peterson et al., 1986), has been hindered by the time-consuming effort required to obtain needed quantities of meiofaunal organisms. For example, to measure carbonstable and nitrogen-stable isotope composition of nematodes, assuming an individual dry weight of 2.5 ,ug (Sikora et al., 1977), about 8,000 debris-free nematodes (20 mg dry weight) are required. At least 500 mg dry weight of nematodes is required to prepare antisera for immunoassay studies. However, adequate quantities of clean, debris-free nematodes are necessary if such biochemical techniques are to be feasible. No published account of a single procedure exists which describes rapid extraction of large quantities of living, chemically unaltered nematodes that are free of sediment or detrital particles. Microscopic hand-sorting, as recommended by Hulings & Gray (1971), requires at least 15 h to obtain 8,000 debris-free nematodes. Centrifugal flotation techniques using sucrose (Heip et al., 1974), or colloidal silica (de Jonge & Bouwman, 1977; Nichols, 1979; Schwinghamer, 1981) are not applicable where living, chemically unaltered meiofaunal organisms are required. Colloidal silica is toxic; sucrose may be absorbed or assimilated by the organisms. A simple extraction procedure was devised, based on a modification of the Baermann funnel (Oostenbrink, 1960), in which glass beads or sterile dune sand are used as a filtering layer. Extraction relies on downward migration of nematodes from concentrated natural sediments, through glass beads or sterile sand, into clean, filtered seawater. Contribution Number 685 from the Belle W. Baruch Institute for Marine Biology and Coastal Research. This work was supported by NSF Grant OCE85-21345 to B. C. Coull and R. J. Feller. 2 Present address: Institute of Ecology, University of Georgia, Athens, Georgia 30602, U.S.A. TRANS. AM. MICROSC. SOC., 107(1): 96-100. 1988. ? Copyright, 1988, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.112 on Wed, 29 Jun 2016 04:56:14 UTC All use subject to http://about.jstor.org/terms VOL. 107, NO. 1, JANUARY 1988

Migration and development of swim-bladder nematodes, Cystidicola spp. (Habronematoidea), in their definitive hosts

Third-stage larvae of Cystidicola cristivomeri White, 1941, and C. farionis Fischer, 1798, migrated directly via the pneumatic duct to the swim bladder of lake trout, Salvelinus namaycush, and rainbow trout, Salmo gairdneri, respectively. Larvae reached the swim bladder as early as 16 h after fish were infected using a stomach tube. At 4–10 °C, mature male and female C. cristivomeri and C. farionis were first recovered 67 and 210 days, and 112 and 235 days, respectively, after infection. Cystidicola cristivomeri is probably long-lived; there was no evidence that any died in lake trout infected for up to 600 days.Large numbers of third-stage cystidicolid larvae accumulated without maturing in the swim bladder of naturally infected lake whitefish, Coregonus clupeaformis, from Lake Nipigon, northwestern Ontario. When given to rainbow trout, these larvae matured and the adult nematodes were identical to C. farionis. These results suggest that the swim-bladder nematode that matures in lake whitefish is a distinct species.

Experimental infection of mule deer with Parelaphostrongylus tenuis.

Six adult and three fawn mule deer (Odocoileus hemionus) were experimentally infected with a range of 75-100 infective larvae of Parelaphostrongylus tenuis. Five of the six adult deer developed clinical signs of neurologic disease that terminated in paralysis between 35 and 80 days. The sixth deer developed slight signs of neurologic disease for 10 days, but recovered. All three mule deer fawns developed neurologic disease. Adult meningeal worms were recovered from the subdural space of the spinal cord of two fawns. Eggs were observed on the cranial dura mater of one of these fawns, indicating that P. tenuis can complete its life cycle provided mule deer can survive the damage resulting from the infection. Neither eggs nor larvae of P. tenuis were recovered from the feces or lungs of infected mule deer. Clinical signs and histologic lesions observed in experimentally infected mule deer resembled those reported in infected moose (Alces alces americana). Two critical periods were apparent in mule deer infected with P. tenuis: nematode migration through the spinal neural parenchyma, and penetration of the adult nematodes into the cranial neural parenchyma. While most adult deer were unable to survive the first critical period, fawns survived the first but succumbed to infection during the second critical period.

The Influence of Tea Root Saponins On the Recovery of Pratylenchus Loosi From Tea Feeder Roots

A highly significant improvement in the recovery of Pratylenchus loosi Loof from tea feeder roots by a modified Baerman funnel technique was observed with increasing concentrations of small amounts of tea root saponins (1-10 ppm) in the sieve water. Higher concentrations of saponins (>10 ppm), retarded recovery. The improved recovery with weak solutions of saponins was found to be reversed when the latter were bound to sterols. It is suggested that since free saponins have a tendency to bind to cell wall sterols, small concentrations could weaken cell wall membranes and this effect is likely to have facilitated a better migration of nematodes from root tissue. Higher concentrations, on the other hand, could affect nematode tissue themselves and are therefore likely to affect their mobility and consequently their recovery.

Experimental Studies On The Efficacy Of Thiabendazole Against The Migratory Stages Of Ascarids In Mouse

Experimental Studies On The Efficacy Of Thiabendazole Against The Migratory Stages Of Ascarids In Mouse