Portable Cyst Extractor: Detecting Cyst Nematodes in the Field

For on-site detection of cysts, a portable cyst extraction kit was constructed from nine readily available items. The portable cyst extractor detected cysts in a range of 1-117 cysts/100 g soil from 42 fields. Samples processed by this kit in fields were clean and easy to examine, possibly because the kit is a compact version of the standard wet-sieving technique used in the laboratory. The portable cyst extractor has several advantages over traditional survey methods: i) diagnosis of cyst infestations in the field accurately and rapidly most of the year and ii) reduction in the labor of samplings and transportation of soil samples.     

Biocontrol: The Potential of Entomophilic Nematodes in Insect Management

A review of the development of entomophilic nematology and a commentary on the potential of entomophilic nematodes in controlling insect pests. The paper considers some of the major contributions to our knowledge of entomophilic nematology; factors involved in insect pest management and how they are applicable to the use of nematodes; nematodes which are most promising as biological control agents; and problems to be solved to facilitate the use of entomophilic nematodes in insect management.     

Evolution of Parasitism in Insect-transmitted Plant Nematodes

Nematode-insect associations have evolved many times in the phylum Nematoda, but these lineages involve plant parasitism only in the Secernentean orders Aphelenchida and Tylenchida. In the Aphelenchida (Aphelenchoidoidea), Bursaphelenchus xylophilus (Pine wood nematode), B. cocophilus (Red ring or Coconut palm nematode) (Parasitaphelenchidae), and the many potential host-specific species of Schistonchus (fig nematodes) (Aphelenchoididae) nematode-insect interactions probably evolved independently from dauer-forming, mycophagous ancestors that were phoretically transmitted to breeding sites of their insect hosts in plants. Mycophagy probably gave rise to facultative or obligate plant-parasitism because of opportunities due to insect host switches or peculiarities in host behavior. In the Tylenchida, there is one significant radiation of insect-associated plant parasites involving Fergusobia nematodes (Fergusobiinae: Neotylenchidae) and Fergusonina (Fergusoninidae) flies as mutualists that gall myrtaceous plant buds or leaves. These dicyclic nematodes have different phases that are parasitic in either the insect or the plant hosts. The evolutionary origin of this association is unclear.     

Phylogenetic Relationships Based on Ribosomal DNA Data for Four Species of Cyst Nematodes from Italy and One from Syria

Phylogenetic analysis of new ribosomal DNA (rDNA) data for Heterodera mediterranea, H. hordecalis, H. carotae, and H. fici from Italy and H. ciceri from Syria, along with published data for other species, showed high bootstrap support for the following relationships: (((((H. carotae H. cruciferae) H. goettingiana) (((H. trifolii H. ciceri) H. mediterranea) ((H. avenae H. latipons) H. fici))) (Cactodera betulae H. hordecalis)) (Globodera rostochiensis G. pallida)). The rDNA sequence data were for the two internal transcribed spacers (ITS1 and ITS2) plus the 5.8S gene between them. These inferred relationships support the classic ''''Goettingiana Group'''' of H. carotae, H. cruciferae, and H. goettingiana. A clade comprised of Cactodera betulae and H. hordecalis is only distantly related to the other species in the analysis.     

Role of Nematodes and Soil-borne Fungi in Cotton Stunt

The nematodes, Pratylenchus brachyurus, Trichodorus christiei, and T. porosus and the soil-borne fungi, Rhizoctonia solani, Pythium debaryanum, P. irregulare, P. ultimum, and Fusarium spp. were the pathogens most frequently found in the roots and rhizosphere of field-grown cotton (Gossypium hirsutum) showing "stunt" symptoms. Field-plot application of the nematicide D-D (l,2-dichloropropane, 1,3-dichloropropene) at 373.4 liter/ha (40 gal/A) significantly increased plant growth and yield. A fungicidal mixture of Dexon (p-dimethylaminobenzenediazo sodium sulfonate at 23.5 kg/ha (2l lb/A) and Terraclor (pentachloronitrobenzene at 25.2 kg/ha (22.5 lb/A) was phytotoxic, but combined nematicide/fungicide treatments were not. Greenhouse temperature-tank experiments in soils from two locations showed significantly improved root and shoot growth following methyl bromide fumigation at both 25 C and 18 C and more severe "stunt" at the lower temperature.     

Entomopathogenic Nematodes Are Not an Alternative to Fenamiphos for Management of Plant-Parasitic Nematodes on Golf Courses in Florida

With the cancellation of fenamiphos in the near future, alternative nematode management tactics for plant-parasitic nematodes (PPN) on golf courses need to be identified. The use of entomopathogenic nematodes (EPN) has been suggested as one possible alternative. This paper presents the results of 10 experiments evaluating the efficacy of EPN at managing PPN on turfgrasses and improving turf performance. These experiments were conducted at various locations throughout Florida over the course of a decade. In different experiments, different EPN species were tested against different species of PPN. Separate experiments evaluated multiple rates and applications of EPN, compared different EPN species, and compared single EPN species against multiple species of PPN. In a few trials, EPN were associated with reductions in certain plant-parasite species, but in other trials were associated with increases. In most trials, EPN had no effect on plant parasites. Because EPN were so inconsistent in their results, we conclude that EPN are not acceptable alternatives to fenamiphos by most turf managers in Florida at this time.     

Historical Development of Nematology in Russia

The development of Russian hematology is considered from the late nineteenth century to 1970. The dominant influences of I. N. Filipjev and A. A. Paramonov are discussed in the context of the persons whom they influenced and their conceptual approach to the problems posed hy nematodes. The advantages and disadvantages of the framework of Russian scientific administration are compared to those in the West.     

Control of Root-Knot Nematodes on Tomato by the Endoparasitic Fungus Meria coniospora

The endoparasitic nematophagous fungus Meria coniospora reduced root-knot nematode galling on tomatoes in greenhouse pot trials. The fungus was introduced to pots by addition of conidia at several inoculum levels directly to the soil or addition of nematodes infected with M. coniospora to the soil; both methods reduced root galling by root-knot nematodes. These studies represent a part of a recently initiated effort to evaluate the potential of endoparasitic nematophagous fungi for biocontrol of nematodes.     

Population Densities of Nematodes Under Seven Tillage Regimes

Numbers of plant-parasitic nematodes on corn growing under seven tillage regimes were monitored. Differences among treatments occurred for Helicotylenchus pseudorobustus, Pratylenchus spp., Xiphinema americanum, dorylaimids, and total numbers of nematodes. Except with members of the Tylenchinae, highest densities occurred in no-till ridge plots and lowest numbers occurred in spring- and fall-plowed pots.     

Perspectives on the Behavior of Entomopathogenic Nematodes from Dispersal to Reproduction: Traits Contributing to Nematode Fitness and Biocontrol Efficacy

The entomopathogenic nematodes (EPN) Heterorhabditis and Steinernema are widely used for the biological control of insect pests and are gaining importance as model organisms for studying parasitism and symbiosis. In this paper recent advances in the understanding of EPN behavior are reviewed. The “foraging strategy” paradigm (distinction between species with ambush and cruise strategies) as applied to EPN is being challenged and alternative paradigms proposed. Infection decisions are based on condition of the potential host, and it is becoming clear that already-infected and even long-dead hosts may be invaded, as well as healthy live hosts. The state of the infective juvenile (IJ) also influences infection, and evidence for a phased increase in infectivity of EPN species is mounting. The possibility of social behavior - adaptive interactions between IJs outside the host - is discussed. EPNs’ symbiotic bacteria (Photorhabdus and Xenorhabdus) are important for killing the host and rendering it suitable for nematode reproduction, but may reduce survival of IJs, resulting in a trade-off between survival and reproduction. The symbiont also contributes to defence of the cadaver by affecting food-choice decisions of insect and avian scavengers. I review EPN reproductive behavior (including sperm competition, copulation and evidence for attractive and organizational effects of pheromones), and consider the role of endotokia matricida as parental behavior exploited by the symbiont for transmission.     

A Semiquantitative Method for Enumerating and Observing Parasites and Predators of Soil Nematodes

A laboratory method was developed to count and observe antagonists of soil nematodes and simulate their relationships in the soil. A 10- to 25-cc soil sample is suspended in water and washed through a series of small standard sieves. Residues are washed into a small beaker and collected on a 24-mm filter paper disk in a filter holder under vacuum. The disk is placed on corn meal agar in a petri dish. Microfauna and flora present in the sample colonize the organic matter on the disk and move onto and into the agar where they can be observed easily. Distinct successions of organisms usually occur and within 6-18 days or more, parasites and predators of nematodes are often abundant, especially nematode-trapping fungi. Counting predation events and parasitized nematodes in replicate dishes after specific incubation periods allows quantitative comparisons between soil samples. The method has distinct advantages over others for enumerating organisms which attack nematodes.     

Association of Nematodes and Dogwood Cankers

Dogwood canker is a serious production problem of unknown etiology. From May 1985 through April 1989, cankers from 290 flowering dogwood trees in 15 separate nurseries were sampled for nematodes. Seventy-three percent (213) of the cankers contained nematodes. Panagrolaimus rigidus (Schneider) Thorne (115/290) and Aphelenchoides spp. (91/290) were the most frequently collected taxa. Panagrolaimus rigidus was reared on 2% water agar with unidentified bacteria as the food source. Aphelenchoides spp. were reared in antibiotic-amended agar culture with the fungus Glomerella cingulata (Stoneman) Spauld. &Schrenk as a food source. Repeated attempts to culture Aphelenchoides spp. on dogwood callus tissue were unsuccessful. Artificially created stem wounds inoculated with combinations of Aphelenchoides spp. and P. rigidus callused completely in 60 days with no indication of canker development. Very low numbers of nematodes were recovered from inoculated trees, but P. rigidus and one Aphelenchoides sp. were efficient dispersers and occurred in treatments other than those in which they were inoculated.     

Impact of a Nematode-parasitic Fungus on the Effectiveness of Entomopathogenic Nematodes

The impact of the nematode-parasitic fungus Hirsutella rhossiliensis on the effectiveness of Steinernema carpocapsae, S. glaseri, and Heterorhabditis bacteriophora against Galleria mellonella larvae was assessed in the laboratory. The presence of Hirsutella conidia on the third-stage (J3) cuticle of S. carpocapsae and H. bacteriophora interfered with infection of insect larvae. Conidia on the J3 cuticle of S. glaseri and on the ensheathing second-stage cuticle of H. bacteriophora did not reduce the nematodes'' ability to infect larvae. The LD₅₀ values for S. carpocapsae, S. glaseri, and H. bacteriophora in sand containing H. rhossiliensis were not different from those in sterilized sand when Galleria larvae were added at the same time as the nematodes. However, when Galleria larvae were added 3 days after the nematodes, the LD₅₀ of S. glaseri was higher in Hirsutella-infested sand than in sterilized sand, whereas the LD₅₀ of H. bacteriophora was the same in infested and sterilized sand. Although the LD₅₀ of S. carpocapsae was much higher in Hirsutella-infested sand than in sterilized sand, the data were too variable to detect a significant difference. These data suggest that H. bacteriophora may be more effective than Steinernema species at reducing insect pests in habitats with abundant nematode-parasitic fungi.     

Early Crop Root Destruction for Management of Tobacco Cyst Nematodes

Prompt tillage after crop harvest was investigated as a cultural control for the tobacco cyst nematode, Globodera tabacum tabacum, on stalk-cut broadleaf cigar wrapper tobacco. Stalk stumps and roots remaining after harvest were destroyed by tilling immediately or from 2 to 6 wk after harvest in field experiments over 4 yr. Cyst nematode Pf/Pi ratios ranged from 0.65 to 1.62 when plants were tilled immediately after harvest and 1.13 to 5.88 when tillage was delayed. Nematode population development was monitored by inoculating plants in pots placed in fields with J2 in eggs and sampling over time (8 to 18 wk). Three generations per year were observed, and G. t. tabacum generation time was as short as 6 wk for each generation. Destroying stalks and root systems remaining after harvesting stalk-cut broadleaf cigar wrapper tobacco removes the host to preclude development of nematodes at the end of the second and entire third generation. Early tillage resulted in consistently lower tobacco cyst nematode populations than allowing viable roots to remain in fields for an additional 8 to 18 wk. This management tactic reduces the need for nematicide application to slow nematode population increases over time and can reduce losses due to infection by G. t. tabacum.     

Distribution of Field Corn Roots and Parasitic Nematodes in Subsoiled and Nonsubsoiled Soil

A field trial was conducted for 2 years in an Arredondo fine sand containing a tillage pan at 15-20 cm deep to determine the influence of subsoiling on the distribution of corn roots and plant-parasitic nematodes. Soil samples were taken at various depths and row positions at 30, 60, and 90 days after planting in field corn subsoiled under the row with two chisels and in non-subsoiled corn. At 30 and 60 days, in-row nematode population densities to 60 cm deep were not affected by subsoiling compared with population densities in nonsubsoiled plots. After 90 days, subsoiling had not affected total root length or root weight at the 20 depth-row position sampling combinations, but population densities of Meloidogyne incognita and Criconemella spp. had increased in subsoiled corn. Numbers of Pratylenchus zeae were not affected. Subsoiling generally resulted in a change in distribution of corn roots and nematodes in the soil profile but caused little total increase in either roots or numbers of nematodes. Corn yield was increased by subsoiling.     

Freezing and Desiccation Tolerance in Entomopathogenic Nematodes: Diversity and Correlation of Traits

The ability of entomopathogenic nematodes to tolerate environmental stress such as desiccating or freezing conditions, can contribute significantly to biocontrol efficacy. Thus, in selecting which nematode to use in a particular biocontrol program, it is important to be able to predict which strain or species to use in target areas where environmental stress is expected. Our objectives were to (i) compare inter- and intraspecific variation in freeze and desiccation tolerance among a broad array of entomopathogenic nematodes, and (ii) determine if freeze and desiccation tolerance are correlated. In laboratory studies we compared nematodes at two levels of relative humidity (RH) (97% and 85%) and exposure periods (24 and 48 h), and nematodes were exposed to freezing temperatures (-2°C) for 6 or 24 h. To assess interspecific variation, we compared ten species including seven that are of current or recent commercial interest: Heterorhabditis bacteriophora (VS), H. floridensis, H. georgiana, (Kesha), H. indica (HOM1), H. megidis (UK211), Steinernema carpocapsae (All), S. feltiae (SN), S. glaseri (VS), S. rarum (17C&E), and S. riobrave (355). To assess intraspecific variation we compared five strains of H. bacteriophora (Baine, Fl1-1, Hb, Oswego, and VS) and four strains of S. carpocapsae (All, Cxrd, DD136, and Sal), and S. riobrave (355, 38b, 7-12, and TP). S. carpocapsae exhibited the highest level of desiccation tolerance among species followed by S. feltiae and S. rarum; the heterorhabditid species exhibited the least desiccation tolerance and S. riobrave and S. glaseri were intermediate. No intraspecific variation was observed in desiccation tolerance; S. carpocapsae strains showed higher tolerance than all H. bacteriophora or S. riobrave strains yet there was no difference detected within species. In interspecies comparisons, poor freeze tolerance was observed in H. indica, and S. glaseri, S. rarum, and S. riobrave whereas H. georgiana and S. feltiae exhibited the highest freeze tolerance, particularly in the 24-h exposure period. Unlike desiccation tolerance, substantial intraspecies variation in freeze tolerance was observed among H. bacteriophora and S. riobrave strains, yet within species variation was not detected among S. carpocapsae strains. Correlation analysis did not detect a relationship between freezing and desiccation tolerance.     

Plant-parasitic Nematodes in Loess Toposequences Planted with Corn

Populations of plant-parasitic nematodes in an Iowa cornfield were studied along north- and west-facing toposequences. Samples were collected monthly during the growing season. The greatest biomass for Xiphinema americanum occurred at the footslope on the north face. Paratylenchus microdorus had its greatest biomass at the summit position, generally more in the west- than in the north-facing slope. Pratylenchus spp. in the roots peaked at the toeslope in the north-facing slope, but at the footslope in the west-facing slope. Helicotylenchus pseudorobustus peaked at the backslope and the toeslope along the north- and west-facing slopes, respectively. Diversity, as computed for each plot by the Shannon-Weiner diversity index, was highest at the backslope in both toposequences.     

Infection Behavior and Overwintering Survival of Foliar Nematodes, Aphelenchoides fragariae, on Hosta

We studied the pathogenicity and overwintering survival of the foliar nematode, Aphelenchoides fragariae, infecting Hosta spp. Nematodes applied to either lower or upper sides of noninjured and injured hosta leaves were able to infect and produce typical symptoms on nine cultivars. Leaves of only four cultivars (Borschi, Fragrant Blue, Patomic Pride, and Olive Bailey Langdon) showed no symptoms of nematode infection. The nematodes overwintered as juveniles and adults in soil, dry leaves, and dormant buds, but not in roots. Nematode winter survival was higher in dormant buds and soil from the polyhouse than in an open home garden. Of the nematodes found in the dormant buds, 35% to 79% were located between the first two outside layers of the buds. The nematodes tolerated 8 hr exposure to 40°C and −80°C in leaf tissues. Relative humidity influenced nematode migration from soil to leaves. The presence of nematodes only on the outer surface of foliage (leaves and petioles) confirmed the migration of A. fragariae on the surface of the plants. Of the total number of nematodes found on the foliage, 25% to 46% and 66% to 77% were alive at 90% and 100% relative humidity, respectively, suggesting that high moisture is required for the survival and upward movement of nematodes. We conclude that A. fragariae can overwinter in soil, infected dry leaves, and dormant buds and migrate in films of water on the outer surface of the plant during spring to leaves to initiate infection.