Toxicity of four veterinary parasiticides on larvae of the dung beetle Aphodius constans in the laboratory

Abstract

The environmental risk assessment of veterinary pharmaceuticals for dung beetles is strongly hampered because no standardized test method is available so far. Therefore, a test with the temperate dung beetle species Aphodius constans was developed. The survival of beetle larvae was determined after exposure to four veterinary parasitical pharmaceuticals (ivermectin, moxidectin, dicyclanil, and praziquantel) representing different treatment regimes, modes of action, and effect levels. The test was performed in the laboratory (three week duration) with fresh dung, as well as formulated (dried, ground, and rewetted) dung as test substrate (i.e., at least one range-finding test, two definitive test runs per pharmaceutical). Ivermectin was the most toxic substance (median lethal concentration [LC50] = 0.88-0.98 mg of active substance per kilogram of dung dry weight [mg a.s./kg dung (dry wt)] followed by dicyclanil (LC50 = 1.5-6.0 mg a.s./kg dung [dry wt]) and moxidectin (LC50 = 4.0-5.4 mg a.s./kg dung [dry wt]), whereas praziquantel showed very low toxicity (LC50 > 1,000 mg a.s./kg dung [dry wt]). The toxicity in fresh and formulated dung differed by a factor of between 1.1 and 4. The comparison with literature data on toxic effects of these substances on dung beetles in the laboratory or in the field is difficult because no results for praziquantel and dicyclanil have been published so far. With the use of data from ivermectin and moxidectin, the test results are on the same order of magnitude as those known from other studies. On the basis of the experiments reported here, it is recommended that this test be standardized in an international ring test so that it can be incorporated into the risk assessment process as described in the respective international guidelines for the registration of veterinary pharmaceuticals.

New screening test to predict the potential impact of ivermectin-contaminated cattle dung on dung beetles

“…This final LC 50 value was of the same order of magnitude as those obtained by Hempel et al [8] (LC 50 880-980 µg a.s. kg −1 dung (d.w.)) when ivermectin was spiked in dung, both using fresh dung as well as dried, grounded and re-wetted dung as the test substrate. Hempel et al [8] showed that the ratio of NOEC (No-Observed Effect Concentration) / LOEC (No-Observed Effect Level)-values for spiked ivermectin ranged from 320 to 800 for dried dung to 310-780 for fresh dung (in µg a.s. kg −1 dung (d.w.)). When considering the concentration of ivermectin in dung collected one day after the topical administration to animals (only for heifers No.…”

“…I), the concentration in dung ranged from 90 to 130 µg a.s. kg −1 (d.w.) and was lower than the NOEC determined by Hempel et al [8]. At day 3, the values ranged from 830 to 1450 µg a.s. kg −1 (d.w.) and were higher than the effect values of the tests performed by Hempel et al [8] (LC 50 , NOEC and LOEC) and obtained in the present work (LC 50 ). At day 12, the concentration values (300-430 µg a.s. kg −1 dung (d.w.)) were close to NOEC but lower than the LC 50 values.…”

“…The concentrations after 9 days exceeded LC 50 values obtained by Hempel et al [8] for ivermectin. Thus, they could adversely affect dung beetles.…”

“…It was not the aim of this paper to decide whether this study has to be adopted as a more general screening approach. However, we consider this test with dung beetles as applicable for different veterinary drugs [8]. For other dung organisms (e.g.…”

Innate olfactory preferences in dung beetles

“…The boxes were incubated at 20±2°C until emergence of the imagos. This rearing method respects a standard procedure for the breeding of A. constans that has been elaborated for testing the effects of veterinary pharmaceuticals on this species (Hempel et al, 2006;Lumaret et al, 2007). Ten eggs were deposited in each box, and 10 boxes were used for each dung type: a total of 400 eggs were deposited on the different substrates, i.e.…”