A method to study slug predation on seedlings in the field

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Dandelion is a commonAsteraceaespecies that populates disturbed sites and gaps within swards where it becomes an important competitor of grasses. The natural control against dandelion includes seedling predation, with slugs, particularlyArion lusitanicus, being the most important in the Czech Republic. However, the study of slug seedling consumption is difficult because naturally established seedlings are not always available. Therefore, we developed a method of exposing laboratory-grown seedlings as bait for slug predation. Dandelion seeds were sown in plastic cups containing a bottom layer of moist substrate. The emerged seedlings were thinned to 20 and displayed in an open area. During 2008–2010, the seedling baits were placed at 15 sites at 1 month intervals throughout the dandelion vegetative season, in parallel with plasticine baits that monitored slug feeding activity. For each 1 month interval, seedling survival was observed for a period of 8 days, and the estimated time to death was calculated; the percentage of surviving seedlings was then recorded. This method of seedling presentation demonstrated that local and temporal variation in seedling survival is correlated with slug feeding activity. The advantage of this technique is that the seedlings in baits may be presented at any place and time, as required by the experimental design; however, we found that the estimated time to seedling death was shorter for the exposed baits than for the naturally established seedlings. The method is suitable for the study of plant species other than dandelion, and also for aims other than the study of spatiotemporal trends in seedling consumption by slugs.

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