Effects of the hormone mimetic insecticide tebufenozide on Chironomus riparius larvae in two different exposure setups

The effects of the molting-hormone agonistic insecticide tebufenozide on la rvae of the midge Chironomus riparius Meigen were tested in two different e xposure setups. After static contamination of first-instar larvae the NOEC, LOEC, and LC50 values were 13.2, 17.4, and 21.14 mug/L, respectively. Semi static exposure of fourth-instar larvae revealed a lower susceptibility of elder larvae (NOEC 30 mug/L, LOEG 60 mug/L, and LC50 81.94 mug/L). In both cases mortality was not immediate; the effects were postponed and almost ex clusively linked to the processes of pupation and emergence. Pupal mortalit y in the semistatic exposure scheme was twice as high in males as in female s during a 100 mug/L treatment. This sex-specific effect probably resulted from the endocrine activity of tebufenozide. Its detection underlines the s uitability of C. riparius as a model organism for investigating effects of endocrine-disrupting chemicals in aquatic insects. (C) 2001 Academic Press.