Movement and infectivity of entomopathogenic nematodes in sandy loam soil from a carrot field in Nova Scotia: a laboratory study
Blatt, S.E. and Barry, S. 2020. Movement and infectivity of entomopathogenic nematodes in sandy loam soil from a carrot field in Nova Scotia: a laboratory study. J. Acad. Entomol. Soc. 16: 1-6
Plain language summary
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.
Entomopathogenic nematodes (EPNs) from the Heterorhabditidae and Steinernematidae families are predators of various insect species across multiple Orders. Use of EPNs as a pest management strategy has been of interest since the 1930s. Under field conditions, EPN’s are challenging to use due to low viability in soils with variable and often low soil moisture levels, particularly in areas where irrigation is not a common practice. Four EPN products from BioBest (B-Green System (Heterorhabditis bacteriophora), Steiner System (Steinernema feltiae), Kraussei System (Steinernema kraussei) and Carpo System (Steinernema carpocapsae)) were evaluated for efficacy to infest Galleria mellonella larvae buried at three depths in sandy loam soil and adjusted to four soil moisture levels. B-Green and Carpo showed the greatest sensitivity to soil moisture with < 50% infectivity when soil moisture levels were < 10%. Kraussei and Steiner had > 60% infectivity at soil moisture levels of 6 and 8% and > 80% infectivity in soils with 10 or 15% moisture. B-Green and Carpo showed low infectivity when Galleria mellonella was buried at 5 or 7 cm, while Kraussei and Steiner had ≥ 60% infectivity at these depths. EPNs showing ability to infect Galleria mellonella across a range of depths and soil moisture levels would be most promising as candidates for pest management under field conditions with moderate rainfall during the summer months.