Abiotic Factors
Fischer-P;Fuhrer-E 1990.Effect of soil acidity on the entomophilic nematode Steinernema kraussei Steiner.
Biology-and-Fertility-of-Soils, 9: 2, 174-177; 18 ref.
The free-living stages of Steinernema kraussei (Rhabditida), an endoparasite of Cephalcia abietis L. (Hymenoptera), are exposed to different soil conditions when searching for host nymphs. Field studies and laboratory experiments showed that soil acidity plays a major role in the nematode's ability to parasitize Cephalcia nymphs. Under field conditions in Picea abies forests positive correlations between soil pH and both nematode density and insects parasitized were found. Acidic soil with pH levels below 4.0 may limit the nematode's host-finding. Controlled experiments in the laboratory under different pH conditions confirmed these correlations.
Kung-SP;Gaugler-R;Kaya-HK 1990.Influence of soil pH and oxygen on persistence of Steinernema spp. Journal-of-Nematology, 22: 4, 440-445; 17 ref.
Survival of infective juveniles of Steinernema carpocapsae [Neoaplectana carpocapsae] and Steinernema glaseri [N. glaseri] gradually declined during 16 weeks of observation as the tested soil pH decreased from pH 8 to pH 4. Survival of both species of Neoaplectana dropped sharply after 1 week at pH 10. Survival of N. carpocapsae and N. glaseri was similar at pH 4, 6 and 8 during the first 4 weeks, but N. carpocapsae survival was significantly greater than N. glaseri at pH 10 for 16 weeks. N. carpocapsae and N. glaseri that had been stored at pH 4, 6 and 8 for 16 weeks and at pH 10 for 1 or more weeks were not infective to Galleria mellonella larvae. N. carpocapsae survival was significantly greater than that of N. glaseri at oxygen: nitrogen ratios of 1:99, 5:95, and 10:90 during the first 2 weeks, and survival of both nematode species declined sharply to less than 20% after 4 weeks. Survival of both nematode species significantly decreased after 8 weeks as the tested oxygen concentrations decreased from 20 to 1%, and no nematode survival was recorded after 16 weeks. N. carpocapsae pathogenicity was significantly greater than that of N. glaseri during the first 2 weeks. No nematode pathogenicity was recorded at oxygen concentrations of 1, 5, and 10% after 2 weeks and at 20% after 16 weeks.
Kung-SP 1990.Abiotic factors affecting the persistence of two entomopathogenic nematodes, Steinernema carpocapsae, and Steinernema glaseri (Nematoda:Steinernematidae) in the soil.
Dissertation-Abstracts-International.-B,-Sciences-and-Engineering. 1990, 51: 4, 1620; Abstract of thesis, Rutgers State University of New Jersey, USA, 134 pp.,available from University Microfilms International.
Persistence of two steinernematid nematodes, Steinernema carpocapsae and Steinernema glaseri were studied at different soil type, pH, oxygen, temperature, moisture, and relative humidity under laboratory conditions. Soil type tests revealed that nematode persistence was greater in sandy than in clay soils. Nematode persistence decreased as clay contents in the soil increased. Soil pH tests showed that the soil pH at the ranges of most agricultural soils (pH 4-8) had no adverse effects on nematode persistence. However, persistence drastically declined when soil became highly alkaline at pH 10. Soil oxygen tests demonstrated that nematode persistence decreased as soil oxygen concentrations decreased from 20 to 1%. Soil temperature tests indicated that S. carpocapsae persistence was greater at low (5-25°C) than high temperature (35°C). Conversely, S. glaseri persistence was greater at high (15-35°C) than low temperature (5°C). The differences may be attributed to differences in the climatic origins of these two nematode species. Soil moisture tests demonstrated that persistence of S. carpocapsae and S. glaseri was greater at suprisingly low moistures (2 and 4%, respectively), as compared with higher moistures (8 and 16%). These two nematodes are far better at surviving desiccation by slowing the rate of water loss at reduced soil moistures (2-4%). Relative humidity tests were conducted to simulate the type of desiccation that occurred in the soil and indicated that persistence of these two nematode species decreased as RH decreased from 100 to 25% over the 32-d test period. S. carpocapsae persisted 32 days at 100% RH, 16 days at 97% RH, 8 days at 90% RH, 4 days at 75% RH, and 2 days at 50 and 25% RH. S. glaseri persisted 32 days at 100% RH, 16 days at 97% RH, 4 days at 90% RH, 12 h at 75% RH, and 4 h at 50 and 25% RH. S. glaseri appeared more susceptible to environmental conditions than S. carpocapsae.
Blackshaw-RP; Senthamizhselvan-M. 1991. The effect of sand particle size on Steinernema feltiae sensu Filipjev (1934) ( = N. bibionis Bovien) activity against Galleria mellonella larvae.
Annals-of-Applied-Biology, 118: 3, 637-643; 10 ref.
The activity of an isolate of Steinernema feltiae [Neoaplectana feltiae] in different fractions of sand was measured by the mortality of host Galleria mellonella larvae. No deaths were recorded in particles less than 600 µm across. Maximum activity occurred with 700-800 µm size particles. Activity was also limited with a sand fraction containing particles of 1000-1100 µm. Host mortality in mixtures of two sand fractions varied. Generally, the addition of either small particles (500-700 µm) or large ones (1000-1100 µm) to fractions of the mid-range (700-1000 µm) reduced the percentage kill of host larvae. Polynomial regression models fitted to data from single-phase experiments could be used to predict accurately mortality of G. mellonella larvae in two-phase mixtures of sand.
Infectivity of native populations of Steinernema spp. and Heterorhabditis indica in sand and sandy loam soil columns against Agrotis ipsilon (Hufnagel).
Hussaini-SS; Singh-SP; Parthasarathy-R; Shakeela-V
Annals-of-Plant-Protection-Sciences. 2000, 8:2, 200-205; 12 ref.
Infectivity of four populations of Steinernema spp. and Heterorhabditis indica alone and in combinations were evaluated against Agrotis ipsilon in sand and sandy loam soil columns. H. indica PDBCEN 13.22 outcompeted Steinernema spp. irrespective of soil type, depth and time in terms of A. ipsilon mortality. S. bicornutum PDBCEN 3.1 was found to be promising against A. ipsilon. The performance of all the nematode populations was better in sandy loam soil than in sand at 5 cm depth. The mortality of A. ipsilon was enhanced by increasing the time of exposure. A combination of Steinernema carpocapsae PDBCEN 6.11 and H. indica PBBCEN 13.22 had an additive effect over the control achieved by their individual populations in both soil types at 10 cm depth.
Effect of soil depth and moisture on the vertical distribution of Steinernema riobrave (Nematoda: Steinernematidae).
Gouge-DH; Smith-KA; Lee-LL; Henneberry-TJ 2000
Journal-of-Nematology, 32:2, 223-228; 23 ref.
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).
Portillo-Aguilar-C; Villani-MG; Tauber-MJ; Tauber-CA; Nyrop-JP1999. Entomopathogenic nematode (Rhabditida: Heterorhabditidae and Steinernematidae) response to soil texture and bulk density.
Environmental-Entomology, 28: 6, 1021-1035; 40 ref.
The survival of Heterorhabditis bacteriophora Oswego Poinar, Steinernema carpocapsae NY001 Weiser, and S. glaseri NCl Steiner varied in relation to the bulk density of a sandy loam soil. Survival of H. bacteriophora decreased linearly with time (4-70 days) and quadratically with increasing bulk density, whereas S. glaseri survival decreased linearly with time, but increased quadratically with increasing bulk density. Survival of S. carpocapsae decreased quadratically with time, but was unaffected by bulk density. H. bacteriophora and S. glaseri infected larvae of the greater wax moth, Galleria mellonella (L.) for up to 10 weeks after soil inoculation, and the incidence of infection showed no significant variation in relation to bulk density or time. In contrast, infection rate by S. carpocapsae increased with bulk density and decreased with time. The combined effects of soil texture and bulk density on movement these of nematode species generally decreased as the bulk density of 3 soil textures increased. However, the degree to which soils of high bulk density reduced movement differed among species and soil textures: H. bacteriophora was the least restricted; whereas, S. carpocapsae was the most restricted. All 3 species moved significantly more in sandy loam, than in loam or silty clay loam. Although movement was reduced at relatively high bulk densities, survival of the 3 nematode species was high. Rates of movement and infection by the nematodes were strongly correlated with the amount of soil pore space having dimensions similar to or greater than the diameters of the nematodes. In a sandy loam soil, H. bacteriophora moved at least 18 cm within 4 days of soil inoculation across all bulk densities tested, whereas S. carpocapsae moved only 9 cm at the 3 lower densities and <9 cm at the highest soil density. S. glaseri showed intermediate levels of movement.
Chinnasri-B; Tangchitsomkid-N; Somsook-V; Nanta-P; Buncha-Chinnasri; Nuchanart-Tangchitsomkid; Vacharee-Somsook; Pimolporn-Nanta; Oates-CG (Editor) 1999
Influence of soil texture and soil moisture on survival and subsequent infectivity of entomopathogenic nematode, Steinernema carpocapsae (All strain).
The 37th Kasetsart University Annual Conference, 3-5 February, 1999. 1999, 326-332; 7 ref.
Influence of soil texture and moisture on survival and subsequent infectivity of Steinernema carpocapsae (All strain), was examined. The highest percentage of nematode survival was observed in sandy loam soil (59.3%) while intermediate and low survival were found in sand (47.5%), sandy clay loam (7.2%) and clay loam (6.6%), respectively. The testing of the nematode infectivity showed that the juveniles could maintain 100% of their infectivity in sandy and sandy loam soil but diminished to 14 and 9% in sandy clay loam and clay loam, respectively. The effects of soil moisture on survival and infectivity of infective juveniles were also elucidated. At 6% (w/w) soil moisture, the nematode survival was highest throughout nine weeks of the study. The differences in survival and infectivity of entomopathogenic nematodes in various soil textures and moisture levels are due to the size of soil pores, oxygen and water in the soil.