Effect of the nematode Phasmarhabditis hermaphrodita on young stages of the pest slug Arion lusitanicus

In a soil bioassay, adult Deroceras reticulatum (Stylommatophora: Limacidae) and three different weight-classes of young Arion lusitanicus (Stylommatophora: Arionidae) were exposed to a single dosage (170 dauer larvae per g of soil) of the nematode Phasmarhabditis hermaphrodita monoxenically associated with the bacterium Moraxella osloensis, Groups of 10 slugs were continuously exposed to nematodes for 4 days, and then transferred individually to Petri-dishes containing a disc of Chinese cabbage as food. Food consumption-measured by image analysis-and slug mortality were recorded daily for 10 days. Food consumption was inhibited in both slug species tested. D. reticulatum stopped feeding 6 days after the start of nematode treatment, while all A. lusitanicus continued to feed. However, in the three weight-classes of A. lusitanicus (0.15 g, 0.24 g, 0.45 g), food consumption was reduced by at least 50 %. The greatest reduction in feeding, nearly 90 %, was noted in the smallest A. lusitanicus. The nematodes successfully killed D. reticulatum but were less efficient at killing young A. lusitanicus. At the end of the experiment, mortality was highest in D. reticultatum (98 %) and the smallest weight-class of A. lusitanicus (47 %). There was almost no mortality in the largest weight-class of A. lusitanicus treated with nematodes. P. hermaphrodita, associated with M. osloensis can thus be considered as a biological control agent for young stages of A. lusitanicus for its effect as a feeding inhibitor, rather than for its ability to kill the slugs.