The effectiveness of entomopathogenic nematodes (EPN) against pest insects is largely dependent on the method of application and nematode survival under field conditions. Nematodes must persist long enough to control pest populations, despite sensitivity to abiotic factors such as desiccation and UV light. Here we investigate the use of compost as a carrier medium for the entomopathogenic nematode Steinernema feltiae, since co-application with compost could potentially mitigate some of the negative environmental constraints of EPN application. We tested three application methods in combination with six composts of different biological maturity (defined using the Nematode Index of Compost Maturity (NICM). EPN in composts were applied to a soil and incubated in 1L pots for 12 weeks. The application methods used were aqueous application (AA), non-formulated infected host cadavers (NFC) and formulated infected host cadavers (FC). Destructive sampling was used at 4, 6, 9 and 12 weeks to test for entomopathogenic nematode survival (via extraction and enumerations) and nematode virulence based on Galleria mellonella mortality. After 12 weeks of incubation, survival ranged from 3.2% in control pots with AA, to 62% found in a mature compost applied with formulated cadavers. FC and NFC application and the use of more mature composts resulted in an improved survival. Application method had significant effects on virulence, NFC and AA had higher G. mellonella mortality than FC. A NICM immature compost significantly decreased virulence compared to a NICM mature compost, although neither were significantly better than the control. These results suggest that both application method and biological quality of a compost have to be considered for co-application of compost and EPN. Thus, the use of compost enriched with host cadavers may be an environmentally friendly way to suppress pest insects on farms while simultaneously improving soils through compost application, though economic viability would still need assessment.
Herren, G. L., Binnemans, I., Joos, L., Viaene, N., Ehlers, R. U., Vandecasteele, B., … Steel, H. (2018). Compost as a carrier medium for entomopathogenic nematodes – The influence of compost maturity on their virulence and survival. Biological Control, 125, 29–38. https://doi.org/10.1016/j.biocontrol.2018.06.007