Chemoreception and feeding in the grey field slug, Deroceras reticulatum (Müller), with reference to molluscicide formulation
Studies on Deroceras reticulatum (Müller), the grey field slug, indicate that this animal is responsive to food odours and can therefore. select its food. Olfactory responses to food odours are monitored by distance chemoreceptors while contact chemoreception is responsible for the gustatory stimuli associated with taste. Both types of sensory perception are important in the feeding cycle. The former has been investigated with the aid of a timelapse camera and the behaviour of slugs monitored in the presence of various food materials and their components. Gustatory responses have been assessed by a feeding assay which permits the quantitive analysis of food ingested. These two aspects of feeding behaviour have been combined to provide a framework for the improved formulation of slug baits for use in agriculture. The two molluscicides metaldehyde and methiocarb have been compared in laboratory and field tests for their efficiency in poisoning slugs and their effects on soil fauna. The field results, which included comparisons between laboratory and commercial metaldehyde formulations, indicate the importance of monitoring the residual population of slugs which remains after baiting. It appears that the true level of bait efficiency may be obscured if tests are concerned only with recording the number of poisoned animals trapped. The addition of a mammal repellent to slug baits does not appear to adversely affect their attraction to slugs but individual formulations may vary considerably in both their palatability and their effectiveness. The laboratory feeding tests have suggested that Derbceras reticulatum habituates to certain diets and that the feeding response may decline over a few days - this can be restored by presenting a novel food to the animals. The meal size of this species can be manipulated in the laboratory by altering the diet'and by the addition of attractive components. Some attempt has been made to define these compounds with a view to improving the consumption of baits by slugs in the field.