Soil moisture effects on the activity of three entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) isolated from Meghalaya, India

Entomopathogenic nematodes (EPNs) are obligate parasites of insects that are widely distributed in soils throughout the world. They have great potential for use as biological control agents for insect pests. It is known that strains of Steinernema and Heterorhabditis isolated from different geographical regions exhibit differences in their ecological traits, such as infectivity, establishment, survival, reproduction, etc. A precise knowledge of these factors is therefore an essential pre-requisite for devising successful strategies to use these nematodes in biological control programmes. The present study investigated the effect of soil moisture on the activity (as measured by number of nematodes established in hosts) of three entomopathogenic nematode species (Heterorhabditis indica Poinar, Karunakar & David; Steinernema thermophilum Ganguly & Singh; Steinernema glaseri Steiner), isolated from forest soils in Meghalaya, India, under laboratory conditions. The experiments for EPNs were conducted at 25 ± 2°C (30 ± 2°C for S. thermophilum) in a sandy loam soil (85% sand, 12% silt and 3% clay, pH 6.54). Last instar larvae of wax moth, Galleria mellonella served as the experimental insect host. The soil moistures tested were 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22 and 25% (w/w). The study revealed that soil moisture has marked influences on establishment of infective juveniles of different nematode species in insect host. While, S. thermophilum showed establishment at 4% and above soil moistures, H. indica and S. glaseri showed establishment at 5% and above soil moistures. The optimum soil moisture for different nematode species were noted as: H. indica 8–18%, S. thermophilum 6–20%, and S. glaseri 8–25%. Further, a minimum of 6% soil moisture was noted to be essential for achieving 100% host mortality for all the three nematode species.