Movement and infectivity of entomopathogenic nematodes in sandy loam soil from a carrot field in Nova Scotia: a laboratory study

Entomopathogenc nematodes (EPNs) are microscopic worms that feed on a wide range of soil-dwelling insect species. In the soil they locate a host and use it as a source of food and refuge during their reproductive stage. Specific species have been isolated, cultured and developed into commercial products. Four of these products were sourced from BioBest and used in a laboratory study to better understand how they will move and locate a host in sandy loam soil, a common soil type used in vegetable production. Pest species that could be affected by EPNs include carrot rust fly and carrot weevil. Soil was collected from a nearby carrot field, autoclaved and used in a laboratory study. Cardboard mailing tubes were cut into 10 cm lengths and lined with a wax paper tube. Soil was adjusted to soil moisture levels of 6, 8, 10 and 15% and a waxworm (Galleria species) was buried at depths of 3, 5 or 7 cm. Every combination of soil moisture and depth was tested, with 10 tubes within each replicate and 5 replicates for each treatment. Four products (B-Green, Steiner System, Carpo System and Kraussei System) were applied to the soil surface and left for 48 hours. After this time, the waxworms were recovered and dissected to confirm the presence of EPNs. Two of the products, Steiner System and Kraussei System, were able to locate and infect the waxworm more than 50% of the time no matter the depth or the soil moisture level. Carpo System could locate the host more than 40% of the time only if buried to a depth of 3 cm but did so at low soil moisture levels (6 and 8%). B-Green System was able to locate the host when buried at the 5 and 7 cm depths, but only if the soil moisture level was 15%. These studies show the differences in mobility and infectivity between commercially available EPN species. Selecting the appropriate EPN as a pest management strategy needs to consider where, in the soil, the target pest will be located, and the amount of moisture in the soil. Failure to consider these factors will likely not result in effective control of the target pest.