J. Iglesias

Field Test Using the Nematode Phasmarhabditis hermaphrodita for Biocontrol of Slugs in Spain

An experiment was carried out between May and July 1999 in Galicia (North-West Spain) to test the capacity of the nematode Phasmarhabditis hermaphrodita to protect field grown lettuces from slug damage in our field conditions. The experiment compared a single dose of nematodes (3 2 109 ha -1) with mini-pellets containing 5% metaldehyde, applied at the recommended field rate (3 g pellets m -2), and untreated plots. Slug damage for each lettuce head was estimated on six dates during the first 4 weeks after planting. At harvest, each lettuce head was weighed, scored as marketable or not by weight and external aspect, and inspected for slugs. Metaldehyde significantly reduced slug damage to lettuce plants from the first day after planting to the third week. Nematodes significantly reduced slug damage from the second to the third week. At harvest, 6 weeks after planting, the mean weight of the lettuce heads and the number of marketable heads in the nematode plots were as good as in the metaldehyde plots, and both treatments were significantly better than the untreated plots. The number of slugs within the harvested plants was significantly reduced only with the metaldehyde treatment.

Utilization of weeds and crop plants by the pest slug, Deroceras reticulatum (Müller, 1774)

ABSTRACT Feeding of the slug Deroceras reticulatum was studied over 2 years in a garden characterized by the simultaneous presence of a variety of weeds and cultivated plant species. Monthly, twenty slugs were captured during night searches and their crop contents were analysed in the laboratory. Overall, 24 different items were identified in the crop contents, 21 were of vegetable origin and three of animal origin. Most (68.2%) of the studied animals had eaten more than one plant. The quantitative contribution of each food item to the crop contents was assessed as the percentage represented by its fragments in relation to the total surface area of the crop contents. Green vegetable materials represented 85.4%, dead vegetable materials 11.7%, and animal materials 2.9% of the crop contents. Only six green plants individually contributed more than 5%: grasses, Stellaria media, Lactuca sativa, Brassica oleracea, Sonchus oleraceus and Ranunculus repens. The abundance of weeds in the garden was not correlated with the contribution of weeds or cultivated plants to the crop contents. The abundance of cultivated plants was not correlated with their own contribution to the crop contents, but was negatively correlated with the contribution of weeds. The contribution of weeds and cultivated plants to the crop contents of the slugs were negatively correlated.