Size-specific susceptibility of the pest slugs Deroceras reticulatum and Arion lusitanicus to the nematode biocontrol agent Phasmarhabditis hermaphrodita

The nematode Phasmarhabditis hermaphrodita is a commercially available biocontrol agent against slugs. This product is especially interesting for use in organic farming, where products containing metaldehyde or carbamates cannot be used for controlling pest slugs. We investigated the potential of P. hermaphrodita for the control of the pest slugs Deroceras reticulatum and Arion lusitanicus. These two species are the most harmful slug pests in Switzerland. At different times of the year, we collected slug specimens of different weight and assessed their susceptibility to P. hermaphrodita in the laboratory. Batches of five slugs were subjected to five different doses of nematodes plus an untreated control and replicated three times. During six weeks, feeding and survival of the slugs were recorded. D. reticulatum was strongly affected by increasing nematode doses, irrespective of the slugs' body weight. In small specimens of A. lusitanicus, feeding and survival were strongly affected by the nematodes, while larger specimens remained almost unaffected. Because A. lusitanicus has an asynchronous development in Switzerland, it seems difficult to control the entire population with a single nematode application. To what extent nematodes will be used in practice for slug control depends on their effectivity against the pest slugs of major importance, on the longevity of the molluscicidal effect and on the price of nematodes.