On the cultivation of free-living marine and estuarine nematodes

Although a large body of literature exists on the systematics and ecology of free-living marine and brackish-water nematodes, key questions on the nature and magnitude of interactions between nematodes and other organisms in the benthos remain unanswered. Relatively few authors have investigated live nematodes in food web studies or in experiments dealing with the nematodes’ response to a varying environment. It is mainly for the latter purpose that attempts have been made to maintain, rear and cultivate selected species. This paper describes the methodology used for the maintenance, rearing, and eventual permanent agnotobiotic cultivation of a variety of estuarine nematodes. Spot plates, where small samples of sediment or macrophyte material are inoculated on a sloppy agar layer, have been used for the purpose of maintenance and initial cultivation. Those species that reproduce on spot plates are then selected for monospecific cultivation on agar layers with different nutrient enrichments and with micro-organisms cotransferred from the spot plates as food. Mixtures of bacto and nutrient agar prepared in artificial seawater were specifically suitable for the xenic cultivation of nine bacterivorous and, when supplied with Erdschreiber nutrients, two algivorous/bacterivorous nematode species. Up to three generations of five other nematode species have been reared under laboratory conditions, and several more were kept alive and active for variable periods of time on agar. Generation times observed on spot plates forAdoncholaimus fuscus andOncholaimus oxyuris were substantially shorter than previously published estimates and suggest a correspondingly higher predatory and scavenging potency for these and related enoplids. A procedure for the long-term storage of nematodes at −80°C with glycerol as a cryoprotectant was successfully used forDiplolaimella dievengatensis, Panagrolaimus sp. 1, andPellioditis marina, but not forDiplolaimelloides meyli. The authors have also summarized the existing literature on the cultivation of marine and brackish-water nematodes. Continuous cultivation appears to have been successful mainly for Aufwuchs and epiphytic nematodes; only few sediment-dwellers have been established in permanent culture. Of only just over 30 species that have ever been cultivated, more than half belong to one family (Monhysteridae) and three are Rhabditida, an order poorly represented in the marine environment. Four species have been grown in monoxenic and one in axenic culture, the latter though with limited success. It is concluded that our understanding of the basic nutritional requirements of marine nematodes is as yet insufficient, and that the culture techniques which have so far mainly deployed agar or liquid substrates, while being suitable for the cultivation of Aufwuchs and epiphytic nematodes, do not accurately enough mimic gradients specific of the natural habitat of many sediment-dwellers.     

The Structure of a Free-living Nematode Community in Wrangel Bay of the Sea of Japan

The qualitative composition and distribution of the meiobenthos in Wrangel Bay (Nakhodka Bay of the Sea of Japan) depend on the bottom sediment grain composition and on the concentration of heavy metals in the ground. It was established that the meiobenthos in the bay was represented by 13 groups of animals (class, order) and was relatively evenly distributed. The nematodes dominated (50–80%), and their settlement density was slightly higher in silty ground than in silty–sandy ground. Forty-eight species of nematodes were found; Dorylaimopsis peculiaris, Viscosia stenostoma, Axonolaimus seticaudatus, Metasphaerolaimus japonicus, and Pseudosteineria inaequispiclata dominated in the silty–sandy sediments; Sabatieria pulchra, S. palmaris, Metalaimus pumilus, Sphaerolaimus limosus, and Oncholaimium ramosum dominated in the silty ground. A slightly expressed correlation of the settlement density with the ground type and lead concentration in the bottom sediments emerged for two species (S. pulchra and S. palmaris).     

Development of Four Populations of Meloidogyne hapla on Two Cultivars,of Cucumber at Different Temperatures

The infectivity and development of four populations of Meloidogyne hapla were compared, at three temperatures, on tomato and two varieties of cucumber. A population from Canada produced few root-galls on cucumber and, except at 24 C, no larvae developed into adult females and produced egg masses. In contrast, a population with 45 chromosomes from America produced many galls on cucumber and small proportions of larvae became females and produced egg masses at 20 and 24 C. At 18 C this population produced no egg masses on cucumber, but a population from Britain and one from America with 17 chromosomes produced more egg masses at this temperature than at 20 or 24 C. Dissection of the galls showed that on cucumber many larvae died or their growth and development was slowed.     

The Sex Ratio of Heterodera glycines at Low Population Densities

The sex ratio of the Arkansas 1 isolate of Heterodera glycines was determined in experiments in which ''Lee'' soybean was inoculated with either one or two larvae. A 3:1 male to female sex ratio was established for this isolate under the test conditions used. No influence of one nematode on the penetration and development to adult of another nematode in the same root was detected in double larval inoculations.     

Benthic nematodes in acidified lakes: case of a neglected grazer

Abundance and composition of nematode fauna were examined in the benthic microbial mats and upper sediment layer of the littoral of acidified (pH 4.6 to 5.7) lakes. Nematodes constituted from 58% to 90% of all the invertebrates present (excluding protozoans and rotifers). In the examined material, the majority of nematodes was represented by 3 taxa of which Ironus was found specifically associated with the mats. It was concluded that the persistence of benthic mats may be linked to the metabolic activity of the associated nematode fauna.     

Application of the most probable number method to estimations of entomopathogenic nematode populations in soil

The calculation of most probable numbers (mpn) was used for the estimation of numbers of infective entomopathogenic nematodes in soil. The mpn concept was first introduced in bacteriology as a means of estimating numbers of organisms in a substrate without a direct count, in cases where direct enumeration could not be applied. In the work reported here, soil samples infested with infective juveniles (IJs) of Heterorhabditis megidis (isolate HF85) were diluted with uninfested soil and the diluted soils were baited with mealworm larvae (Tenebrio molitor). The mpn of infective units of IJs in the undiluted soil was calculated. The mpn calculation was found to be applicable to entomopathogenic nematodes in soil under particular conditions. It could be successfully applied to data for the response of soil units but not to the data based on the response of individual insects, as the latter did not confirm to a Poisson series. The calculated mpn represented between 2.9 and 7.1% of the initial inoculum of IJs. It was suggested that IJs might act as a group in infecting an insect host. Using the data for Tenebrio mortality on parasitisation, the mpn based on quantal response of the mealworms would therefore not give the true density of IJs in the soil sample but the effective density, or the quantity of infective units. Although the biological significance of the infective unit needs further clarification, mpn was found to be a useful parameter for use in comparative experiments.     

Behavioral Effects of Carbofuran and Phenamiphos on Pratylenchus vulnus. II. Attraction to Bean Roots

Pratylenchus vulnus (L₃, L₄, adults) are attracted to the roots of growing bean seedlings. The attraction is inhibited by treating the nematodes with solutions of carbofuran or phenamiphos at concentrations below those necessary to inhibit motility and dispersion. Nematicide treatments of plants without treatment of nematodes are ineffectual because nematodes are attracted equally well to treated and untreated seedlings.     

Population Dynamics of Belonolaimus longicaudatus and Criconemella ornata and Growth Response of Bermudagrass and Overseeded Grasses on Golf Greens Following Treatment with Nematicides

Portions of a ''Tifgreen'' bermudagrass golf green with poor turf and large numbers of Belonolabnus longicaudatus and Criconemella ornata were treated with selected nematicides in the summers of 1977 and 1978. Improvements in turf quality were observed within 4 wk after treatment with phenamiphos and fensulfothion. Treatment with phenamiphos restulted in lower numbers of B. longicaudatus 4 and 14 wk after treatment in the 1977 experiment and up to 1 yr after treatment in the 1978 experiment. Treatment with fensulfothion reduced the number of B. longicaudatus for only 1 month after treatment and significantly increased the numbers of this nematode in September and March in the 1978 experiment, Negative correlations were obtained between numbers of B. longicaudatus and turf qualily up to 1 yr. Numbers of C. ornata were reduced only in January and June following treatment with phenamiphos and not at any time with fensulfothion. Treatment with fensulfothion resulted in higher numbers of this nematode than in check plots in November and March. The percent area covered by prostrate spurge the following year was reduced following treatment with phenamiphos, but not with fensulfothion.     

Plant Sources of Chinese Herbal Remedies: Effects on Pratylenchus vulnus and Meloidogyne javanica

More than 500 plant species, used alone or in combination, are documented in Chinese traditional medicine to have activity against helminth and micro-invertebrate pests of humans. We subjected 153 candidate medicines or their plant sources to multilevel screening for effectiveness against plant-parasitic nematodes. For extracts effective in preliminary screens, we determined time-course and concentration-response relationships. Seventy-three of the aqueous extracts of medicines or their plant sources killed either Meloidogyne javanica juveniles or Pratylenchus vulnus (mixed stages), or both, within a 24-hour exposure period. Of 64 remedies reported as antihelminthics, 36 were effective; of 21 classi- fied as purgatives, 13 killed the nematodes; of 29 indicated as generally effective against pests, 13 killed the nematodes. Sources of extracts effective against one or both species of plant-parasitic nematodes are either the whole plant or vegetative, storage or reproductive components of the plants. Effective plants include both annuals and perennials, range from grasses and herbs to woody trees, and represent 46 plant families.