Structural and functional responses of benthic invertebrates to imidacloprid in outdoor stream mesocosms

This study explored structural and functional responses of benthic macroinvertebrates in a mesocosm to imidacloprid. The formulated product Admire (imidacloprid) was used to approximate edge-of-field runoff scenarios at 2 µg/L and 20 µg/L (average of 1.63 and 17.60 µg/L, respectively). Functional responses were evaluated for the stonefly Pteronarcys comstocki in the mesocosm and lab, as well as for other benthic invertebrates that were inoculated in the mesocosm. The mesocosm experiment lasted 20 days and included 24 hour pulses of imidacloprid every seven days. Stonefly feeding was assessed in the same conditions as the mesocosm by measuring the remaining food and the stonefly weight at the end of the 20 day experiment. Oxygen consumption was determined in the lab for P. comstocki that were exposed to 0, 2, 10, or 20 µg/L for 24 hours. The higher level of imidacloprid (17.6 µg/L) in the mesocosm caused reductions in total benthic insects, as well as a 69% decline in Ephemoptera, Plecoptera, and Tricoptera abundance (pooled together), and a 75% decline in Oligochaete density. There were no significant effects on dipterans. Decomposition of leaf matter in coarse bags was significantly reduced in the treated streams with a higher imidacloprid dose. P. comstocki feeding rates were significantly lower for the higher concentration treatment. The lower imidacloprid dose (1.63 µg/L) did not cause any significant effects in the mesocosms.  Oxygen consumption was only significantly different from the control at 10 µg/L and 20 µg/L. Overall, the authors saw effects on the macroinvertebrate communities at 17.6 µg/L.

Pestana, J.L.T., A.C. Alexander, J.M. Culp, D.J. Baird, A.J. Cessna, and A.M.V.M. Soares
Environmental Pollution
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