Survey of slug-associated nematodes to control a key soybean seedling pest in the Eastern US

Terrestrial slugs, notably Deroceras laeve and D. reticulatum cause substantial damage to soybean and corn grown using conservation agricultural techniques. Current management relies on molluscicide pellets and baits that are toxic to non-target organisms and often ineffective. Natural enemies like nematodes, on the other hand, have proven effective in controlling slugs in Europe. However, a key hinderance to biocontrol with nematodes in the Eastern US is the lack of knowledge about which species are present and can thus be deployed and promoted on the farm. Here, we surveyed corn and soybean fields to determine the presence, diversity and distribution of nematodes associated with native and introduced slugs in the Mid-Atlantic. A total of 2,598 slugs were collected between 2022 and 2023 from 19 sites located in Maryland and Delaware. Just 117 of the collected slugs were parasitized by nematodes, representing 4% of those collected in 2022 and 5% in 2023. Using molecular sequence data (18S ribosomal region) we have so far identified five nematode species. Some species appear to be phoretic and necromenic, while others may be true slug parasites. We are currently expanding our survey efforts to nearby Eastern US states and conducting pathogenicity trials to confirm parasitism and thus validate their biocontrol potential. Though we have yet to find Phasmarhabditis hermaphrodita and P. californica, two commercialized mollusk-parasitic nematodes, in the Eastern US, our ongoing research efforts remain focused on determining the biocontrol potential of our nematodes and identifying ways to promote them on the farm.