Several streams near Baie Comeau, Quebec were treated with a particulate formulation of methoxychlor (particle size 8–15 μ) or Abate® (particle size 2.5–20 μ) at a dosage of 0.1 ppm for 15 min to determine if such a formulation is effective against and selective for black fly larvae. The effects of these larvicides were evaluated by sampling the stream fauna before and after treatment with cones, Surber samplers, drift nets, and rock sampling. A new caging device, the entrapment sampler, was used to assess mortality directly.
Both larvicides were effective against Simuliidae. Neither particulate insecticide was completely selective for black fly larvae, since philopotamid larvae and some chironomid larvae were also killed. Although some other detritus-feeding insects also were affected, numerous families of insects including potential predators of Simuliidae were not affected appreciably by these particulate larvicides. Particulate Abate affected a few more families of insects than particulate methoxychlor. The comparative effects of these formulations and the corresponding liquid formulations on stream fauna are discussed. Particulate formulations are a promising alternative to the present formulations used for black fly larviciding, and further research on their safety and performance and on methods of aerial application is recommended.