Slug-parasitic and entomopathogenic nematode presence in Delaware soils”

• Kara Hegge, Environmental Science, University of Delaware

• Michael Crossley, Entomology & Wildlife Ecology, University of Delaware
• Thabu Mugala, Entomology & Wildlife Ecology, University of Delaware

Slugs are important agricultural pests that cause damage to corn and soybean seedlings grown in conservation agricultural systems in Delaware. To control slugs, growers often use molluscicides, usually formulated using metaldehyde. However, metaldehyde is harmful to wildlife, non-target insect species, and humans. To mitigate this, there are natural methods of slug pest management, such as the use of slug-parasitic nematodes. Pellioditis hermaphrodita has been identified and isolated on the West Coast of the United States. Nevertheless, to date it has not been isolated on the East Coast and has the potential for biological control. These nematodes are commonly surveyed by isolating them directly from the slugs. While this approach identifies nematodes that are actively associated with slug hosts, it may also overlook other nematode species that may be soil-dwelling but not actively infecting slugs. To address this, we collected and identified nematodes from soil samples obtained from agricultural fields and adjacent woodlands to identify the soil properties that favor the presence and diversity of slug-associated nematodes. The least nematode-related mortalities were found from the sampling location characterized by a leaf litter forest, and the most were found in the deciduous forest sampling location. Soil with a higher moisture content yielded less nematode related deaths while soil with a higher pH yielded more, which suggests that taking these qualities into account when searching for nematodes may be useful. However, overall the number of nematode related mortalities for slugs was not high enough to suggest that this method is more effective in the search for nematodes than keeping slugs without soil. Getting slug samples from inside of crop fields stands as the more effective approach in the hunt for a more sustainable method of pest management.