Competition between two steinernematid nematode species for an insect host at different soil depths.

We studied interactions between 2 entomopathogenic nematode species, Steinernema carpocapsae, an ambusher forager, and Steinernema glaseri, a cruiser forager, when they were provided wax moth larvae as hosts at 0, 2, or 10 cm soil depth. Populations of infective juvenile nematodes in soil were monitored at 30-day intervals over 120 days using wax moth larvae as baits. After application of S. carpocapsae, S. glaseri, or the combination of both species, hosts were added at 30-day intervals. With hosts at 0 cm depth, each nematode species was negatively affected by the presence of the other species at the 30- and 60-day samples. At 90 and 120 days, S. carpocapsae numbers in the combined treatment were as high as in the single species treatment, whereas only few S. glaseri were recovered. With hosts at 2 or 10 cm depth, the presence of S. glaseri had a strong negative effect on S. carpocapsae, but S. glaseri was not affected by the presence of S. carpocapsae. In another experiment, S. carpocapsae dominated over S. glaseri in hosts located at 0 cm depth as measured by penetration efficiency into hosts and progeny production. In contrast, S. glaseri dominated at 2 cm depth. At 2 cm depth, S. carpocapsae penetrated into hosts too slowly to compete successfully with S. glaseri. Steinernema carpocapsae is superior to S. glaseri when competing for a host on the soil surface; however, below the surface S. glaseri is superior to S. carpocapsae.