By Lisa M. Ames
Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science. December 1990
This study examines some effects of selected soil factors on the insect parasitic nematode Steinernema scapterisci. The main objectives of the study were to examine the influence of soil texture on the motility of juveniles of S. scapterisci and to assess the effects of soil moisture on their survival.
The dispersal of S. scapterisci was evaluated in a sand (98% sand, 0% silt, 2% clay), a loamy sand (89.5% sand, 1.5% silt, 9% clay), a sandy clay loam (77% sand, 1% silt, 22% clay) and an organic soil. Motility was assessed in lab assays which used an insect host, Acheta domesticus (the house cricket), as an indicator of nematode dispersal.
The ability of S. scapterisci to reach and infect hosts decreased as the clay content of the soil increased from 2 to 22%. The percent of available hosts infected was significantly lower for the sandy clay loam soil than for the other soils tested. Dispersal of infective juveniles was not significantly affected by an organic soil.
The influence of soil moisture on juveniles of S. scapterisci was evaluated for moistures ranging from above field capacity to below wilting point in two loamy sand soils and a sandy soil. In sand, survival was compared to a related insect parasite, S. carpocapsae (All strain). Juveniles of S. scapterisci survived up to 13 weeks at wilting point (15 bars moisture tension) in all soils tested. At moistures below wilting point, juveniles survived longer in a sandy loam (87.5% sand, 9% silt, 3.5% clay) than in a sand (98% sand, 0% silt, 2% clay). Nematode survival did not decrease significantly over the period of the experiments (8 or 13 weeks) for most of the soil moistures tested. All juveniles recovered from the soils infected house crickets in petri dish tests.
In the sand soil, significantly more S. scapterisci survived longer in soil moisture levels at wilting point and below than did S. carpocapsae (All strain). Fewer than 2% of the juveniles of S. carpocapsae were recovered after 5 weeks at moisture levels below wilting point. Recovery for juveniles of S. scapterisci, however, was still above 57% at 5 weeks and showed no significant decrease over an 8 week period at the same moisture level in this soil.