Entomopathogenic nematode (Rhabditida: Heterorhabditidae and Steinernematidae) response to soil texture and bulk density

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 d) 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 wk 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 d 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.