PMID: 19270970;PMCID: PMC2620435;Abstract:
The effect of soil moisture on the distribution of Steinernema riobrave in a sand column was determined. Larvae of Pectinophora gossypiella were used to detect S. riobrave infective juveniles (IJ) in each 2.5-cm section of 30-cm-long soil columns. Soil moisture was determined for each section and related to the numbers of nematodes recovered from infected insect baits. Infective juveniles of S. riobrave applied on the sand column surface showed some degree of positive geotaxis. IJ in soil columns with a consistent moisture gradient grouped in the upper 12.7 cm within a water potential range of -40 to -0.0055 MPa (2% to 14% moisture). Nematodes in sand columns that were gradually dehydrating moved down the soil column, aggregating on the 28th day between 15-23 cm in depth. Nematode redistribution over time allowed IJ to remain within a water potential range of -0.1 to -0.012 MPa (5.2% to 9.5% moisture).
Galleria mellonella L. larvae were infected with three species (seven strains) of Steinernema spp. or three species (three strains) of Heterorhabditis spp. Infected larvae were incubated at 22, 27, and 32°C. Larvae were dorsally dissected every 6 h over a 48-h period. Hemolymph was collected and streaked on tryptic soy agar plates. Several non-symbiotic bacterial species were identified from infected insect cadavers: Enterobacter gergoviae, Vibrio spp., Pseudomonas fluorescens type C, Serratia marcescens, Citrobacter freundii, and Serratia proteomaculans. At 18-24 h incubation, the nematode-associated symbiont occurred almost exclusively. Bacterial associates generally appeared outside the 18-24 h window. Infective juveniles of Steinernema feltiae (Filipjev) (27), Steinernema riobrave Cabanillas, Poinar, and Raulston (Oscar), or Steinernema carpocapsae (Weiser) (Kapow) were left untreated, or surface sterilized using thimerosal, then pipetted under sterile conditions onto tryptic soy agar plates. Several additional species of associated bacteria were identified using this method compared with the less extensive range of species isolated from infected G. mellonella. There was no difference in bacterial species identified from non-sterile or surface sterilized nematodes, suggesting that the bacteria identified originated from either inside the nematode or between second and third stage juvenile cuticles. Infective juveniles of S. feltiae (Cowles), S. carpocapsae (Cowles), and H. bacteriophora Poinar (Cowles) were isolated from field samples. Nematodes were surface-sterilized using sodium hypochlorite, mixed with G. mellonella hemolymph, and pipetted onto Biolog BUG (with blood) agar. Only the relevant symbionts were isolated from the limited number of samples available. The nematodes were then cultured in the laboratory for 14 months (sub-cultured in G. mellonella 7-times). Other Enterobacteriaceae could then be isolated from the steinernematid nematodes including S. marcescens, Salmonella sp., and E. gergoviae, indicating the ability of the nematodes to associate with other bacteria in laboratory culture. © 2005 Elsevier Inc. All rights reserved.
In laboratory bioassays, Steinemema riobrave Cabanillas, Poinar and Raulston (355 strain), Steinernema carpocapsae (Weiser) (Mexican 33 strain), Steinernema feltiae (Filipjev) (UK76 strain), and Heterorhabditis bacteriophora Poinar (HP88 strain ) were all capable of infecting and killing three termite species, Heterotermes aureus (Snyder), Gnathamitermes perplexus (Banks), and Reticulitermes flavipes (Kollar) in laboratory sand assays. S. riobrave and S. feltiae caused low levels of Reticulitermes virginicus (Banks) mortality under the same conditions. At 22°C, significant mortality (≥80%) of worker H. aureus and G. perplexus was caused by S. riobrave, in sand assays, indicating the need for further study. Because of the short assay time (3 d maximum), reproduction of the nematodes in the target host species was not recorded. All nematode species were observed to develop to fourth-stage juveniles, preadult stages, or adults in all termite species with the exception of R. virginicus. Only S. riobrave developed in R. virginicus. Nematode concentration and incubation time had significant effects on the mortality of worker H. aureus. S. riobrave consistently generated the highest infection levels and mortality of H. aureus in sand assays. © 2006 Entomological Society of America.
Diapausing larvae of Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), were exposed to entomopathogenic nematodes (Nematoda: Steinernematidae; Heterorhabditidae) at a dosage of 100 or 200 infective juveniles (IJ) per larva. No significant differences between infection of Steinernema riobrave (strain 355) Cabanillas, Poinar and Raulston, and Heterorhabditis bacteriophora (strain Cruiser) (Poinar) were observed after either 6-d or 9-d of incubation. No significant difference in infection levels occurred due to increasing dose. Greatest insect mortality occurred due to parasitism by S. riobrave (355). In a second assay, diapausing larvae of P. gossypiella were exposed to S. riobrave (355), Steinernema carpocapsae (strain Kapow) (Weiser), H. bacteriophora (strain Lawn Patrol), or H. bacteriophora (Cruiser) at dosages of 50, 100,200, or 400 IJs per larva. S. carpocapsae and H. bacteriophora (Cruiser) infected larvae at significantly higher rates compared with H. bacteriophora (Lawn Patrol) and S. riobrave. A significant difference in infection levels occurred due to nematode dose. In a third assay cotton bolls infested with diapausing P, gossypiella were exposed to S, riobrave (355), or H. bacteriophora (Cruiser). Boxes were prepared with bolls buried 5 cm below the soil surface or bolls laid on the soil surface. Boxes also were incubated at constant temperature or exposed to ambient seasonal temperatures and light. H. bacteriophora (Cruiser) infected larvae at significantly higher rates compared with S. riobrave (355). Significant differences in infection levels occurred due to the location of the boll placement and the incubation temperature.
In laboratory bioassays, Steinernema glaseri Steiner, Steinernema riobrave Cabanillas, Poinar & Raulston, Heterorhabditis bacteriophora Poinar, and Heterorhabditis marelatus Liu & Berry were capable of infecting and killing the bark scorpion, Centruroides exilicauda (Wood). Steinernema feltiae (Filipjev) and Steinernema carpocapsae (Weiser) failed to infect C. exilicauda at 22°C. S. glaseri, H. marelatus, and H. bacteriophora caused significant mortality at 22°C, indicating the potential role of these parasites as a biocontrol option. Efficacy of S. glaseri and H. bacteriophora was reduced in an assay conducted at 25°C. Only S. glaseri was able to reproduce in the target host. Dissection of scorpions at the end of the experimental periods revealed inactive juvenile S. riobrave, H. marelatus, and H. bacteriophora nematodes. Both mermithid and oxyurid nematodes have been documented as nematode parasites of scorpions, but rhabditids have not been reported until now. Field studies are warranted to assess the usefulness of entomopathogenic nematodes as biocontrol agents of bark scorpions. © 2005 Entomological Society of America.