The rhabditid nematode Phasmarhabditis hermaphrodita as a potential biological control agent for slugs

A nematode, Phasmarhabditis hermaphrodita, known to be associated with slugs but not previously thought to be parasitic, was shown to be a parasite capable of killing the pest slug Deroceras reticulatum. The parasite infects slugs in the area beneath the mantle surrounding the shell, causing a disease with characteristic symptoms, particularly swelling of the mantle. Infection leads to death of the slug, usually between seven and 21 days afterwards. The nematode then spreads and multiplies in the cadaver. In an experiment where individual D. reticulatum were exposed to different numbers of P. hermaphrodita, a significant positive relationship was found between nematode dose and slug mortality. In two experiments on host range, the nematode was found to infect and kill all pest slug species tested: Deroceras caruanae, Arion distinctus, Arion silvaticus, Arion intermedius, Arion ater, Tandonia sowerbyi and T. budapestensis, in addition to D. reticulatum.     

Species-specific Detection of Predation by Coleoptera on the Milacid Slug Tandonia budapestensis (Mollusca: Pulmonata)

Tandonia budapestensis is one of the most damaging species of slug in the UK , and can cause major losses in potatoes and cereals . No previous attempts appear to have been made to investigate the potential of natural enemies to control this slug . Monoclonal antibodies can be used to analyze the crop contents of predators collected from the field , in order to detect and quantify the remains of major pest species and identify important natural enemies . A species - specific antibody was therefore raised that could distinguish between T. budapestensis and all other molluscs tested . The antibody could detect as little as 5.57 ng of prey protein in an enzyme - linked immunosorbent assay . It could clearly identify the remains of T. budapestensis among the crop contents of the carabid Pterostichus melanarius for more than 26 h at 16 o C , while the half - life of the antigen within the predator was 12.8 h . Such intervals make it a highly suitable antibody probe for quantifying predation during the previous day . The only serious cross - reactivity problem was with earthworms . The antibody can now be used to test predators collected from the field to see if they are indeed consuming this slug , or whether , as suggested by feeding trials , adult T. budapestensis are to some degree toxic to beetles and therefore avoided .     

Biocontrol of Slugs in Protected Lettuce Using the Rhabditid Nematode Phasmarhabditis hermaphrodita

In two experiments, the rhabditid nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench to soil at four dose rates (3 108, 1 109, 3 109 and 1 1010 ha-1) 1 or 4 days before planting lettuce seedlings in a polythene tunnel. The effects of the four nematode doses on slug damage during the first 3 weeks after planting and on the numbers of slugs found within and below lettuce plants at harvest were measured. Results were then compared with untreated plots and with plots where methiocarb pellets were applied at the recommended field rate. In the first experiment, methiocarb pellets significantly reduced the percentage of plants damaged by slugs, but the nematode did not. In the second experiment, methiocarb pellets and the second highest dose of nematodes significantly reduced the percentage of plants damaged by slugs. The different effect of the nematode in the two experiments may have resulted from differences in the timing of nematode application and/or differences in the pattern of slug damage between experiments. At the end of the first experiment, the highest two doses of nematodes and methiocarb pellets had significantly reduced the number of slugs found within lettuce plants at harvest and on the soil surface below the plants. At the end of the second experiment, analysis of variance showed no significant effects of any treatment on slug numbers or biomass, but regression analysis showed significant negative relationships between nematode dose and total slug numbers, numbers of Arion ater agg. and biomass of Deroceras reticulatum. In both experiments, increasing nematode dose significantly reduced the numbers of slugs found contaminating the harvested lettuce. At the end of the second experiment, the mean weight of individuals of A. ater agg. increased with rising nematode dose.