EFFECTS OF TEMEPHOS ON MACROBENTHOS IN A STREAM OF MT.TSUKUBA

Abstract

Drifting pattern of macrozoobenthos in a stream after the application of emulsifiable temephos and subsequent changes of the fauna were studied. The drift of benthos began in general following the peak of the concentration of insecticide at respective points. However some species delayed further in their drift. Simulium larvae belonged to the early drifting group. These drift patterns generally corresponded to the susceptibility to the insecticide. Hydropsyche ulmeri survived in all the regions. The benthos in the upperstream and the subtributaries, which were not exposed, seemed not to contribute to the recolonization. Three months after the treatment. Chironomid larvae outbroke. This outbreak was followed with the increase of Baetis sp. These results seemed to be caused by the lack of predators and competitors. The destruction of fauna provoked the bloom of algae. The blooming algae was a subordinate species in this region. This bloom also provided food for chironomids.