The Relative Toxicities of Several Pesticides to Naiads of Three Species of Stoneflies

Static bioassays were conducted to determine the relative acute toxicities of some insecticides, herbicides, fungicides, a defoliant, and a molluscicide to the naiads of three species of stonefly, Pteronarcys californica, Pteronarcella badia, and Claassenia sabulosa. Toxic effects were measured by determination of median lethal concn (~~50) for 24-, 48-, and 96-hr exposures, at 15.X Endrin and dieldrin were the most and DDT the least toxic of the chlorinated hydrocarbon insccticidcs tested. Parathion was the most toxic organophosphate insecticide to P. californica naiads, but dmsban was the most toxic to P. badia and C. sabulosa naiads. Trichlorofon (Dipterex) was the least toxic to all three species. P. badia, the species of smallest size, was the species most susceptible to most pcsticidcs, followed in descending order of sensitivity by C. sabulosa and P. californica. Smaller specimens of P. californica naiads were consistently more susceptible to some insecticides than larger specimens of the same species.