World Congress of Malacology Antwerp ... - Unitas Malacologica

anging stimuli driving farmers to adopt minimum tillage practices. Despite various considerable
gains for soil, its ecosystem and farm revenues there is a number of constraints reported to be
associated with the minimum tillage regimes. Besides elevated infestation incidences for weeds and
some plant diseases slugs are considered as a third significant pest problem threatening different
arable crops. This is in particular true for oilseed rape. Following the principles of Integrated Pest
Management (IPM) the deliberate exploiting of husbandry techniques is listed as preferred option in
slug control strategies. Aiming at these objectives a multi-annual study was setup at Berolzheim/
Germany to explore potential impacts of different soil management regimes on slug abundance and
slug damage to Oilseed rape. These investigations were performed between 2001 and 2005
comparing effects of three distinct soil management systems on the Field Grey Slug (Doreceras
reticulatum). These included shallow ploughing (SP),, tine cultivation (SG) and direct drilling (no-till
system) (DS), each for its own, in combination with seedbed consolidation (roller treatment) and / or
molluscicides. Numbers of slugs trapped by refuge traps (Slug mats), seedlings density (plant counts)
and foliar damage were the used parameters. All trails were performed on alternating fields at
annually changing locations within a commercial farm. The geostatic layout matches a three factorial
Strip-block-design, in which each tillage strip (Strip size: 20-30 x 120-180 m) comprised two roller
(± Roller) and two molluscicides sub-treatments (± Sl-pellets). All sub-treatments were set-up
crosswise to the six soil management strips. Slug pellets (metalldhyde) were applied at the officially
recommended rates 2-4 days after sowing.
The results show extreme annual variations in slug activity with no significant correlation to OSRseedling
density. The highest slug activity density over the study period was recorded in the DS plots,
followed by the SG and SP- treatments. There was a highly significant “year” effect on crop density,
strongly masking both tillage and slug effects. In the average of the study years the highest crop
density was observed in the SP treatment, followed by SG and DS treatments. The corresponding
seedling numbers varied between 9 - 41,0 pl./m².. However, this effect was not consistent and
showed extreme variations. SG- tillage treatment proved in contrast the least fluctuations and highest
consistency in crop stands. Main effects of seedbed consolidation and those of slug pellets treatments
were significant over the experimental years, when compared with no-rolling and no-slug pellets subtreatments.
Between rolling and slug pellets treatments there was remarkable interactions.
Slug pellet treatment tended to elevate the number of OSR-seedlings/ m² independent of the soil
management regime. Rolling the seedbed after crop drilling contributed to higher seedling density in
both DS and SG but not in the SP- treatment.
Local adaptations, races or even species?
Engelke, Sabine
Århus University, Department for ecology & genetics, Ny Munkegade, 8000 Århus C, Denmark,
Email: b972455@biology.au.dk
The distribution of the large Arion slugs in northern Europe has changed dramatically during the last
100 years, partly due to human interventions. The red slug, Arion ater rufus, was introduced into
Denmark in 1913 by two amateur entomologists whereas the brown slug Arion lusitanicus has
expanded its range over the last 50 years, probably because of passive transport among countries.
Today, A. lusitanicus is the widest distributed of the three large Arion slugs and was discovered in
Denmark in 1991. The black slug, Arion ater ater, is native to Scandinavia and northern Germany.
The newly introduced taxa of the large arions may be selfing or have a mixed breeding system, as
hypothesized by some workerswhich could explain the ease by which these taxa have spread in
Scandinavia.
This provided me with the opportunity to investigate aspects of invasion biology, with special
emphasis on breeding systems (viz. self-fertilization versus outcrossing). Therefore, I studied the
population genetic structure of several Danish and German populations of the three taxa using
allozyme electrophoresis and the sequencing of mtDNA genes. I also compared the morphology of
the proximal genitalia of the three taxa.
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