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Within the last decades the slug Arion lusitanicus has expanded its range over wide areas of Europe, in most of them it is now a serious pest. Poland has been invaded relatively recently (since the late 1980s). Considering the ecological importance of the slug, very little is known yet about the mechanism of invasion, establishment of new populations and influence on the native fauna and flora. The analysis of nucleotide sequences of mitochondrial cytochrome oxidase subunit 1 gene (cox1) revealed a great inter- and intrapopulation variation in the Polish populations of A. lusitanicus. The differentiation of all the studied Polish populations of A. lusitanicus is 0.2–2.2%, while two analysed Belgian populations are monomorphic and moderately genetically diverse at 0.8%. This indicates a heterogeneous origin of the Polish populations, probably resulting from multiple independent introduction events. The genotype found in the first four Polish populations (S. Poland) suggests that their origin is different from the remaining populations.
Palatability of 20 plant species to the slugs Deroceras reticulatum (O. F. Müller), Arion lusitanicus Mabille and Arion rufus (Linnaeus) was estimated in laboratory food tests (multiple-choice and no-choice). The rate and degree of damage to seedlings and leaves of weeds, herbs and winter oilseed rape were determined, and plant species preferred or rejected by particular slug species were identified. Brassica napus and Datura stramonium were preferred by all the examined slugs, while Geranium robertianum was rejected. The slug species differed in their preferences for the remaining plant species.
Winter rape is susceptible to damage caused by D. reticulatum (O. F. Müller) mainly in the early phases of the plants’ development. The degree of damage and the size of yield losses depend on the slug population and the grazing activity, which are governed by many environmental factors. Laboratory studies were performed to analyse the rate and amount of damage to rape plants (2–3 leaf stage) caused by D. reticulatum, and the effect of temperature and soil humidity on the slug’s grazing activity. With increasing air temperature (up to 16°C) the amount of damage increased, but the effect was not lasting. The slugs were also active at low temperatures (+1°C), and although their grazing was less intense, the amount of damage after seven days could reach an average of 34%. In laboratory tests, the soil humidity had no marked effect on the amount of damage done by the slugs.
In Poland 30 species of invasive mollusks were found; 11 of aquatic snails, 9 of land snails and 10 of land slugs. The most important in plant production are the following slug species: Arion lusitanicus, A. rufus and A. distinctus. These pests quickly spread throughout the country, create huge populations and often cause significant losses in yielding of vegetables, some agricultural crops (especially winter rape and winter wheat), ornamental, fruit and herbal plants.
This paper presents preliminary results of observations of circadian activities of one of the tested slug species – Arion lusitanicus. The study was conducted in laboratory conditions at two different temperatures 10 and 16ºC. The results showed that slugs were much more active at night than during the day. Most of the time during the day they spent in shelter, but little time devoted to nutrition. Arion lusitanicus slugs activity was significantly lower at 10 than at 16°C.
Spray forms of various chemical compounds including compounds of plant origin, molluscicides, and insecticides were tested in order to investigate their possibilities for reducing damage to young rape plants caused by the slug Arion lusitanicus Mabille, 1868. Among them, abamectin (0.2%), methiocarb (0.5%) and metaldehyde (1.0%) reduced damage to the plants, although metaldehyde remained active for only nine days. These three chemical compounds were not phytotoxic to rape plants, and none of them proved lethal to the slugs at the concentration used. The reduction in rape plant damage was obtained as a result of their deterrent and/or antifeedant action. The results indicate that abamectin has high potential usefulness in protecting winter rape seedlings from slugs.
Slugs are serious agricultural pests. Besides oilseed rape, slugs cause strong damage to all species of winter cereals. Experiments were designed to determine the sensitivity of four species of winter cereals (rye, barley, wheat and triticale) in early stages of plant development to damage caused by the slugs Arion lusitanicus and Deroceras reticulatum. The least damaged by two species of snails were seeds of winter barley. In contrast to cereal grains, seedlings of winter barley were strongly attacked by A. lusitanicus. The damage caused by D. reticulatum to seedlings of four species of cereal was similar.
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