Effects of two common fungicides on the reproduction of Aporrectodea caliginosa in natural soil
Résumé
The use of pesticides in agroecosystems can have negative effects on earthworms, which play key roles in soil functioning such as organic matter decomposition. The aim of this study was to assess the effects of two fungicides (Cuprafor micro®, composed of copper oxychloride, and Swing Gold®, composed of epoxiconazole (EPX) and dimoxystrobin (DMX)) on earthworm reproduction by exposing adults and cocoons. First, adult Aporrectodea caliginosa individuals were exposed for 28 days to 3.33, 10 and 30 times the recommended dose (RD) of Cuprafor micro® corresponding to 25.8, 77.5 and 232.5 mg kg−1 dry soil of copper, respectively, and 0.33, 1 and 3 times the RD of Swing Gold® (corresponding to 5.2 × 10−2 mg DMX kg−1 + 1.94 × 10−2 mg EPX kg−1, 1.55 × 10−1 mg DMX kg−1 + 5.81 × 10−2 mg EPX kg−1 and 4.62 × 10−1 mg DMX kg−1 + 1.74 × 10−1 mg EPX kg−1 respectively), in addition to a control soil with no fungicide treatment. Cocoon variables (production, weight, hatching success, hatching time) were monitored. Second, “naïve” cocoons produced by uncontaminated earthworms were exposed to soils contaminated by the same concentrations of the two fungicides, and we assessed hatching success and hatching time. In the first experiment, cocoon production was halved at the highest copper concentration (232.5 mg Cu kg−1 of dry soil) as compared to the control. Cocoons took 5 more days to hatch, and the hatching success decreased by 35% as compared to the control. In the Swing Gold® treatments, cocoon production was reduced by 63% at 3 times the RD, and the hatching success significantly decreased by 16% at the RD. In the second experiment, only the hatching success of cocoons was impacted by Swing Gold® at 3 times the RD (30% less hatching). It is concluded that the cocoon stock in the soil is crucial for the renewal of populations in the field. The most sensitive endpoint was the hatching success of the cocoons produced by exposed adults. This endpoint and the effects observed on the “naïve” cocoons could be taken into account in pesticide risk assessment.