COMPARISON OF THE TOXICITY OF A SYNERGIZED AND NON-SYNERGIZED INSECTICIDE TO YOUNG TROUT

The use of pyrethroid insecticides is increasing (Elliott 1989; Muelle r-Beilschmidt 1990). These insecticides tend to have short half-lives in the environment and as a class, have very low toxicities to birds a nd mammals (WHO 1989). Unfortunately pyrethroids are very toxic to fis h and other aquatic organisms (Demoute 1989). Resmethrin is a type one pyrethroid which is used as a mosquito and blackfly adulticide. It is available in several formulations, some of which contain the synergis t piperonyl butoxide (PBO). PBO increases the lethality of a particula r dose of resmethrin in target species (Casida 1980). The magnitude of the effect of the synergist on the toxicity of resmethrin to aquatic organisms is largely unknown. The action of this synergist on non-targ et aquatic organisms is likely to be similar to its action on target i nsects (Reinbold and Metcalf 1976). This study compares the toxicity o f two formulations of resmethrin using 96-hr toxicity tests, short exp osure tests, and toxicity tests of aged solutions of these insecticide s. One formulation contains the synergist PBO, and the other is a nons ynergized formulation.