D3057: Evaluating the persistence and effectiveness of entomopathogenic nematodes under laboratory conditions

Entomopathogenic nematodes (EPNs) are insect-parasitic organisms used as biological control agents for a wide variety of pests, including Diabrotica virgifera virgifera. However, limited information is available regarding the persistence of applied EPNs and their interactions with native EPNs in the soil. Therefore, this study assessed the persistence of commercial EPNs applied to soils with and without native EPN communities under laboratory conditions to simulate and better understand interactions in the field. Mesocosms (11.4 L tubs) using corn field-collected soil were established with five replications of six treatments: autoclaved soil with no EPN application (T1); autoclaved soil with EPNs applied at 44 (T2) or 136 (T3) million/hectare; non-autoclaved soil with EPNs applied at 44 (T4) or 136 (T5) million/hectare; and non-autoclaved soil with no EPN application (T6). Subsamples of soil were collected from each treatment before and after (1 and 4 months) EPN application, and baiting assays using Galleria mellonella larvae were conducted to assess EPN presence. There was a marginally significant effect of treatment (P = 0.0575) and no effect of period (P = 0.2214) or their interaction (P = 0.9144) on percent infected larvae. Numerically, T6 had the highest infection rates, indicating presence of native EPN populations. In contrast, T2 and T3 showed low infection, suggesting effectiveness of the autoclaving process and poor persistence of the applied EPNs. Additionally, reduced infectivity in T4 and T5 implied potential antagonistic interactions between applied and native EPNs. The results indicate low persistence of applied EPNs and potential competition with native strains.