The acute toxicity of four herbicides to 0–4 hour nauplii ofCyclops Vernalis fisher (copepoda, cyclopoida)

Conclusions

• 1) When compared with published dataCyclops vernalis Fisher was found to be among the most sensitive crustaceans when exposed to amitrole-T and 2,4-D (free acid).

• 2) The toxiclty of amitrole toC. vernalis was somewhat less than published data forDaphnia magna. The 2,4-D (salt) was shown to be less toxic toC. vernalis than reported toxicity forLepomis macrochirus.

• 3) The toxicity of the commercial formulations was not dependent on the active ingredient content. Amitrole-T with 20 percent active ingredient proved to be more toxic than reagent grade amitrole. The alkanolamine salt of 2,4-D was less toxic than 2,4-D (free acid) to an extent much greater than could be expected from the examination of the acid equivalent of 2,4-D (salt).

• 4) Each of the herbicides examined apparently exhibited more than one mode of toxic action. This was demonstrated by the time-mortality data.

• 5) The method used here would be useful in the determination of effects other than mortality such as instar lengths, rates of molting and susceptability of different naupliar stages to stress factors.