Low field-relevant tebufenozide concentrations affect reproduction in Chironomus riparius (Diptera: Chironomidae) in a long-term toxicity test.

A few studies reporting the effects of tebufenozide, a non-steroidal ecdysone agonist that mimics natural moulting hormones in chironomids exist in the literature. However, nothing is known about its chronic or multigenerational effects on the reproduction of aquatic insects, although tebufenozide is present in aquatic ecosystems. Here, we investigated the chronic toxicity of tebufenozide in two successive generations of Chironomus riparius using nominal concentrations that ranged from 4 to 26.2 µg/L. We started the test from the first instar larvae in the parental (P) generation, quantifying life cycle parameters (emergence, sex ratio, development rate, fecundity and fertility) until the emergence in the subsequent F1 generation. Results showed a reduction in reproduction and a significant decrease in male developmental rate of midges for all treatments, in the F1 generation compared with the P generation (paired t test; p<0.001). Two-way analysis of variance revealed a significant exposure × generation effect on male fraction with male fraction increasing (P generation) or decreasing (F1 generation) with increasing exposure. These effects on C. riparius underline the importance of conducting long-term studies with environmentally relevant concentrations to investigate population-level endpoints for endocrine disrupting chemicals.

Two-generation effects of the chitin synthesis inhibitor, teflubenzuron, on the aquatic midge Chironomus riparius.

Teflubenzuron, a chitin synthesis inhibitor was used in a two-generation test with Chironomus riparius (Insecta) to assess effects over a full life cycle from the first-instar larvae in the parental (P) generation until emergence in the subsequent F1 generation. Sediment spiked with teflubenzuron ranging from 10 to 390.6 µg/kg sediment dry weight (dw) was used. EC50-values for fecundity and fertility were 112.7 and 74.5 µg/kg dw, respectively. Significant adverse effects were observed compared to the solvent control for emergence rate (P < 0.01) and also for developmental rate. No observed effect concentrations values were lower for emergence rate in the F1 generation (62.5 µg/kg dw) than in the P generation (100 µg/kg dw), demonstrating that the F1 generation was more affected than the P generation. Thus, this two-generation test may help detecting population level effects as an amendment to the risk assessment for chronic exposures to endocrine disrupting compounds.

Effects of the insect growth regulator pyriproxyfen in a two-generation test with Chironomus riparius.

Pyriproxyfen a juvenile hormone analoga (JHA) was used in a two-generation test with Chironomus riparius (Diptera). The protocol is an extension of the OECD test methods to test duration from first-instar larvae in the parental (P) generation to emergence of midges in the filial (F1) generation. Test species were exposed to concentrations ranging from 0.001 to 0.1mg/L. The results showed significant adverse effects compared to the solvent control for emergence rate (p<0.001), development rate (p<0.001), fecundity (p<0.05) and fertility of egg ropes but not for the sex ratio. No observed effect concentrations (NOEC), respectively, lowest observed effect concentration (LOEC) values were lower for emergence rate and development rate in the F1 (0.003mg/L, respectively, 0.01mg/L each) than in the P generation (0.01mg/L, respectively, 0.03mg/L). The two-generation test provided additional information, which might be useful in the risk assessment of agrochemicals with potential endocrine effects.