Sub-lethal effects, such as those measured in this study, could imply that mature beetles feeding on dung, even at low concentrations of IVM and MOX, may experience an acute toxicity that would prevent the performance of normal biological activities, such as food detection, intraspecific communication, locomotion and interaction with the environment.
This research also represents one of notably few studies on ML ecotoxicology that incorporates significant toxicological values such as the generation of dose-response curves at different concentrations (e.g., to calculate LOEC and IC values), which will allow for the comparison of ecotoxicity between different molecules in future studies aiming to establish risk assessments of veterinary medicines.
2, and lowest significant observed effect concentration (LOEC) reported from Dunnet’s tests performed in the ANOVA-GLM analyses.
Concentration response curves for inhibition of antennal response by ivermectin (IVM) and moxidectin (MOX), using trimethylamine (A) and ammonia (B) as test odorants. Shaded areas represent the 95% confidence intervals of each model.
Thus, from an environmental point of view, obtained LOEC values indicate that MOX, despite needing more time for its elimination in the faeces could be half as harmful to dung beetles as IVM.
Furthermore, a comparison of the toxic thresholds (IC, thus suggesting an increased environmental risk for dung beetles.Macrocyclic lactones (MLs) are a large family of broad-spectrum antiparasitic drugs derived from fermentation products of soil Actinomycetes: Streptomyces avermitilis, in the case of avermectins, and S. Ivermectin (IVM, an avermectin) and moxidectin (MOX, a milbemycin) are commonly used in veterinary medicine to treat livestock diseases caused by gastrointestinal worms, lung worms and ectoparasites, such as mites and blood-feeding insects.These two drugs differ in their chemical structure mainly in a disaccharide group, present in IVM and absent in MOX, and the presence of a 23-methoxyimino group in MOX and other specific substitutions (Fig. As a consequence of these differences, IVM is a large, highly lipophilic molecule that is relatively insoluble in water, while MOX is considerably more lipophilic, which explains its longer mean residence time in the fat tissues of treated animals, increasing plasma membrane permeability due to an agonistic action on chloride channels present in nerve and muscle cells.In summary, dung beetles seem to be more sensitive to IVM than to MOX residues for both larval survival and brood ball production.However, it is necessary to corroborate the possible differential effect of these antiparasitic drugs on adults at both sub-lethal and pre-lethal levels.In this study, the comparative effects of IVM and MOX on adult dung beetles were assessed for the first time examining both physiological sub-lethal symptoms and pre-lethal consequences after somatic paralysis.Following the same methodological guidelines proposed previously, both the sensorial response of antennae (sub-lethal effect) and irreversible ataxia of somatic muscles (pre-lethal effect) were examined by exposing a model dung beetle species (Scarabaeus cicatricosus (Lucas, 1846); Coleoptera, Scarabaeidae) to both IVM and MOX under different dose concentrations.The substituents that differ from IVM and MOX are highlighted in orange and blue, respectively. Among the non-target organisms affected by these substances, dung beetles are particularly sensitive.Dung beetles are considered one of the most important groups within dung pat assemblages in terms of number of species, abundance, biomass and ecosystem services.Electroantennography recordings showed that both IVM and MOX ingestion negatively but differently affected the antennal olfactory apparatus of S. For both tested odorants, LOECs obtained were 1.0 µg kg (fw) for both IVM and MOX, respectively (Table 1).Fitting the % inhibition of antennal response data to log (inhibitor) vs.