Folia Historico-Naturalia Musei Matraensis - A Mátra Múzeum Természetrajzi Közleményei 10. (1985)

De Wilde, J. J. — Van Goethem, J. L. — Marquet, R.: The distribution of the species of the genus Deroceras Rafinesque, 1820 in Belgium (Gastropoda, Pulmonata, Agriolimacidae)

All records of Devocevas agreste (numbers indicate the year of recording) Undoubtedly, D. caruanae was introduced to Belgium shortly before 1968. Most probably there have been a number of subsequent introductions. However, it would certainly be impossible to ascertain them. It seems obvious to us that the dispersal of this slug took readily place over the whole country, but especially in the northern part. This contrasts with the dispersal of another slug during the same period : Boettgerilla pallens SIMROTH, Ï912, originally known from the Caucasus. The latter became specially widespread in the southern part of Belgium /see J. DE WILDE, J. VAN GOETHÉM 8 R. MARQUET, in press/

. Without any doubt, man is responsible for the introduction and the rapid dispersal of P. caruanae in Belgium : e.g. transport of vegetables, garden plants, wood, etc. D. caruanae is highly synanthropic in Belgium. For detailed argumentation and conclusions, see J. DE WILDE, J. VAN GOETHÉM 8 R. MARQUET, 1984a and 1984b. CONCLUSION Deroceras reticulatum and D. laeve are autochthonous species in Belgium. At present they are very widespread and common, the first being probably the most common landsnail species in Belgium. D. reticulatum can be found in any 10 x 10 km square in Belgium and generally in large numbers. Records from 94% of the sampled 10 x 10 km squares are at our disposal, the remaining 6% having no special significancy

. The species lives in almost any kind of habitat and scarcely fails on rubbishtips. It is a synanthropic species, to be regarded as a major pest of many crops. P. laeve has been recorded up to now in 55% of the sampled 10 x 10 km squares in Belgium, in a wide variety of damp or very damp biotopes

. D. agreste could be autochthonous in Belgium, attaining here the westernmost edge of its actual range. The species seems to be rare in Belgium with a limited number of local populations in the four southern provinces. So far, only 13 records are known from the period 1972-76. However, these populations could also be the result of introductions. Since D. agreste is not synanthropic, the species is mainly thrown on natural ways for dispersal. It is clear that in such a case a rapid dispersal is excluded. 112