The effects of Abate, Dursban, and Methoxychlor and their diluents on black-fly larvae and on “non-target” stream invertebrates were evaluated by means of cone, rock, Surber, and drift samples. Blackfly larvae were found in many post-treatment Surber samples, although concurrent cone and rock samples often indicated that blackfly larvae were either greatly reduced in numbers or eradicated from the streams. The insecticide diluents (H.A.N, and fuel oil) caused detachment of blackfly larvae from cones, but less than that obtained when insecticide was added.
The heavy post-treatment drift of “non-target” invertebrates in treated streams is indicative of a considerable disturbance to the aquatic invertebrate community. However, post-treatment samples indicated that the “non-target” organisms studied were not eradicated from the streams.
There were several indications that the catch of invertebrate drift was altered by pools, which possibly exerted a delaying action on drifters in the treated streams. Most of the drifting invertebrates found in post-treatment drift nets were dead.