Feeding activity and survival of slug Arion lusitanicus (Gastropoda: Arionidae) exposed to the rhabditid nematode, Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae)
Abstract: Slugs are important pests of cultivated plants in Croatia. In many sites slug species Arion lusitanicus (Mabille, 1868) (Gastropoda: Arionidae) has become the most frequent species, which is very hard to control by chemical molluscicides. Since 1996 a biological molluscicide based on nematode Phasmarhabditis hermaphrodita (Schneider, 1859) (Nematoda: Rhabditidae) has been formulated as an effective product for slug control. In order to establish feeding activity and survival of adult A. lusitanicus specimens exposed to parasitic nematode P. hermaphrodita and to compare its efficiency to efficiency of chemical molluscicides, a laboratory experiment was performed. Adult specimens of A. lusitanicus (feeded on lettuce leaves in flower pots) were exposed to P. hermaphrodita, metaldehyde and methiocarb treatments. Food consumption of slug specimens was measured daily. Survival of slugs was observed to their death, up to 30th day. In the first week of investigation, chemical molluscicide treatments were found to differ significantly from the biological product and control. At the treatments treated by nematodes, daily leaf area consumption was also reduced and was significantly different from the control treatment. Food consumption was reduced on both chemical and biological treatments but the most of adult speciments of A. lusitanicus survived and continued to feed. To the end of the second week of investigation, food consumption decreased on all treatments and was mainly uniform with no significant differences between treatments. During the experiment, the slugs were dying within the period of 3 to 30 d at the treatments treated by nematode P. hermaphrodita or in the period of 9 to 24 d at the treatments treated by metaldehyde and methiocarb. Because the tolerance level to slug damages in lettuce market is effectively zero, these results indicate a failure of biological product based on P. hermaphrodita in control of adult specimens of A. lusitanicus as well as a failure of chemical molluscicides. These data point at a great need for integrated control of slug damage which must include cultural and different alternative control measures, not only chemical control.