Temperature moderates impact of formulated moxidectin on seed germination of three temperate grassland species

Abstract

Formulations of macrocyclic lactone anthelmintics such as moxidectin are regularly administered to sheep to combat parasites. A disadvantage of these pharmaceuticals are their side effects on non-target organisms when entering the environment. Little is known about anthelmintic effects on plant reproduction and whether the effects depend on environmental factors. For ecological and methodological reasons, we aimed at testing whether temperature affects the efficacy of a common moxidectin-based formulation on seed germination. We carried out a germination experiment including three typical species of temperate European grasslands (Centaurea jacea, Galium mollugo, Plantago lanceolata). We applied three temperature regimes (15/5, 20/10, 30/20°C), and a four-level dilution series (1:100–1:800) of formulated moxidectin (i.e., Cydectin oral drench). These solutions represent seed-anthelmintic contacts in the digestive tract of sheep shortly after deworming. In addition, a control was carried out with purified water only. We regularly counted emerging seedlings and calculated final germination percentage, mean germination time and synchrony of germination. Formulated moxidectin significantly reduced percentage, speed and synchrony of germination. A 1:100 dilution of the formulation reduced germination percentage by a quarter and increased mean germination time by six days compared to the control. Temperature moderated effects of the anthelmintic drug on germination in all response variables and all species, but in different patterns and magnitudes (significant anthelmintic x temperature x species interactions). In all response variables, the two more extreme temperature regimes (15/5, 30/20°C) led to the strongest effects of formulated moxidectin. With respect to germination percentage, G. mollugo was more sensitive to formulated moxidectin at the warmest temperature regime, whereas P. lanceolata showed the highest sensitivity at the coldest regime. This study shows that it is important to consider temperature dependencies of the effects of pharmaceuticals on seed germination when conducting standardised germination experiments.

Effects of macrocyclic lactone anthelmintics on seed germination of temperate grassland species

“…In formulated MOX (Cydectin), we found the effects on seed germination, especially on germination percentage (GP) and mean germination time (MGT), increase in strength with increasing concentrations for most species, which is in accordance with previous studies (Eichberg et al . 2016, 2022). Across all species, this pattern was similarly observed for formulated IVM (Oramec), but not for the four pure substances, where we found no regularly increasing or decreasing concentration‐specific response patterns.…”

“…At species level, in all six tested ML pharmaceuticals, non‐linear and species‐specific response patterns were found, which is also in accordance with previous studies (Eichberg et al . 2016, 2022). We found that the highest concentration of MLs (10.0 mg·l −1 ) affected seeds of most test species, whereas at lower concentrations (0.1, 1.0 mg·l −1 ) effects were less frequent and less consistent (except for pure abamectin).…”