• Eidt, D.C.
  Martimes Forest Research Centre
  

A  stream  was  injected with fenitrothion and the effects on aquatic arthropods were monitored. It was deter­mined that a dose of insecticide of about 20 µg/L for 4 h, resulting from injection at 49.6 µg/L for 2.5 h, was enough to kill larvae of the stonefly Nemoura (Amphinemura) wui Claassen and to a lesser extent, larvae of the mayfly Baetis sp. prob. herodes Burks, but not other species. Leuctra spp. stonefly larvae in cages were killed at a site 59 m below the injection point of fenitrothion at 69.1 µg/L for 2.5 h, but the effect diminished downstream. Leuctra spp.  larvae in cages buried up to 34 cm in the substrate showed better survival than those resting on the stream bed.