SPATIAL PATTERNS OF ENTOMOPATHOGENIC NEMATODES IN MICROCOSMS - IMPLICATIONS FOR LABORATORY EXPERIMENTS

Laboratory microcosms were used to: i) measure the effects of soil moi sture on survival of Steinernema riobravis and ii) investigate the sui tability of using microcosms to study motility and survival of these n ematodes. Nematodes recovered from soil contained in petri dishes decl ined by more than 95% during 7 days, whereas nematodes recovered from the inner surfaces of dishes increased 35-fold. After 7 days in dishes , >20 times as many nematodes were recovered from dish surfaces than f rom soil. Nematodes exhibited a negative geotropism; greater numbers o f nematodes were recovered from the lid surfaces than from the surface s of dishes. Survivorship of nematodes in soil in plastic centrifuge t ubes was somewhat greater than in petri dishes, and fewer nematodes as cended above the soil line in tubes than dishes. Downward migration of nematodes was inversely related to soil column diameter, possibly due to relatively unimpeded movement along container surfaces. An assay w as developed by which nematodes were rinsed from the inner surfaces of centrifuge tubes into the soil. The resulting slurry was then process ed on Baermann trays to recover motile nematodes. Nematode survival in soil in centrifuge tubes was higher at soil moistures between 2-4% th an at lower (0.5-1.0%) and higher (4.0-12.0%) moisture levels. Surviva l of S, riobravis may be enhanced by quiescence induced by moisture de ficits.