DETRIMENTAL EFFECTS OF FENTHION (QUELETOX® UL), USED TO CONTROL RED-BILLED QUELEA (QUELEA QUELEA), ON RHEOPHILIC BENTHIC MACROINVERTEBRATES IN THE ORANGE RIVER

Summary The relative abundance of rheophilic macroinvertebrates in the Orange River was assessed before and 15 hrs after two aerial applications of fenthion (QUELETOX® UL) above roosting sites of the red-billed quelea (Quelea quelea). The first treatment had no detectable effect on benthic macroinvertebrate abundance, whereas the second treatment caused mortality among at least 17 taxa (over half the taxa present). The most sensitive species were nymphs of the mayflies Baetis glaucus and Tricorythus discolor, followed by larvae of the midge Rheotanytarsus fuscus. Fenthion had no detrimental effect on the population densities of the mayfly Afroptilum excisum. The results of this study warn of the dangers of fenthion in water supplies. It is suggested that alternative methods of quelea control along the Orange River should be sought.