Effects of macrocyclic lactone anthelmintics on seed germination and seedling establishment of grassland species

Macrocyclic lactones (MLs) are used as anthelmintics to treat livestock and pets against infections by endo- and ectoparasites. After treatment, these substances are excreted into the environment via faeces, where they persist and harm a wide range of non-target organisms. While the effects of MLs on insects are well known, effects on plants remain understudied. Plants can come into contact with MLs either when they take these substances up from the soil, in which faecal residues of recently treated livestock have been trampled into or when their seeds germinate in faeces of treated livestock. A recent study has found effects of moxidectin, a commonly used anthelmintic, on seed germination and seedling emergence from livestock faeces. Moxidectin reduced these parameters, suggesting that MLs could be a factor for the decline of biodiversity of temperate grassland species in Europe. Therefore, this study was conducted to expand the knowledge on the effects of MLs on seeds, seedlings and growing plants. Three experiments focussing on different steps of the development of plants were conducted, focussing on the effects of several MLs on germination, seedling emergence from faeces of treated livestock and growth during repeated exposures to MLs. This study shows, that the impacts of MLs on seeds, seedlings and growing plants are more extensive than previously expected. Especially for the regeneration of open landscapes, where the spread of seeds via endozoochory is very important. Regeneration of plant coverage could be delayed or stopped completely, affecting whole populations. This study showed new and unexpected effects of MLs on plants and should be seen as a starting point for additional research concerning this far reaching and understudied topic.


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