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Laboratory bioassays were conducted with some chlorinated hydrocarbon insecticides, organophosphate insecticides, other insecticides and acaricides, and with herbicides to determine their relative toxicities and immobilization values for two species of daphnids, Daphnia pulex and Simocephalus serrulatus. Both species are satisfactory bioassay organisms for the determination of a wide variety of pesticides, with D. pulex being the more sensitive. The organophosphate insecticides were generally more toxic than the chlorinated hydrocarbons to both species. DDVP was the most toxic compound investigated. DDT was the most toxic chlorinated hydrocarbon tested, and lindane the least. There was a wide range in the toxicity of hydrocarbons to D. pulex, with 48‐hour EC50 values ranging from 0.36 to 460 ppb. DDT was 2.9 times more toxic at 50 F than at 80 F. Malathion was 8.8 times more toxic at 50 F than at 70 F to S. serrulatus. Endrin was 12 times more toxic than dieldrin to D. pulex. DDT was 2.6 times more toxic at 60 F to first‐instar organisms up to 18 hours old than to 7‐day‐old organisms.

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. INTBODUCTIONThe Plecoptcra are well-represented in North America, and their immatures form an important part of stream ecosystems in this country. Many fishes, especially the trouts, use stonefly naiads as major portions of the diet. The subject of this paper is the amounts of pesticides that kill stonefly nymphs.Our knowledge of the toxicity of pesticidcs to aquatic insects is currently limited to a few species and a few pesticides. Gaufin, Jensen, and Nelson ( 1961) conducted static bioassays with naiads of three species of stoneflies, Pteronarcys cakifomica Newport, Acroneuria pacifica IIagen, and Claassenia sabulosa Banks. These investigations revealed vast differences among the organic insecticides in toxicities to the three species. As an example, parathion was the most toxic of the insecticides to A. pacifica, with an Lc so of 1 part per billion at 96 hr and DDT was the least toxic to the same species with an LC~~ of 410 parts per billion. Jensen and Gaufin (1964a) made a similar study oE the acute effects of 10 organic insecticides on the same two species. Continuous-flow bioassays were later conducted by Jensen and GauEin (1964b) to determine long-term effects on P. californica and A. pacifica naiads; toxicities of some organic phosphate insecticides to the two species of naiads after 96 hr were essentially the same as measured by static and continuous-flow assays. That study also showed that normal molting was inhibited in concentrations that did not kill the naiads. Bridges and Cope (1965) made static bioassays to determine the relative acute toxicities of similar formulations of pyrethrum and rotenone to P. califomica naiads.This study was designed to determine the relative acute toxicities of several pcsticidcs to three species of stonefly naiads under static conditions. The species were chosen for the work because they were readily available and easily maintained in the laboratory. The investigation also included work on the relationship between toxicity and animal size. MATERIALS AND...

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Bluegills (Lepomis macrochirus) were exposed to the propylene glycol butyl ether ester of 2,4‐D in six ponds at Tishomingo, Oklahoma, one concentration per pond in five ponds, and a control pond. The fish and the pond environment were studied for five months to measure chronic effects on the fish and persistence of the herbicide in pond water, bottom sediments, and aquatic vegetation. Small quantities of 2,4‐D were found in pond waters for six weeks after application. Residues of 2,4‐D were found in vegetation and in bottom sediments in the highest‐treated pond for six weeks. No 2,4‐D was detected in fish after four days. One‐fifth of the fish treated at 10 ppm died within 8 days; mortality was almost negligible among bluegills exposed to 5 ppm or less. Spawning among bluegills treated at 10 and 5 ppm was delayed about two weeks. Growth was faster among bluegills in these high‐treatment ponds than in the low‐treatment ponds which received 1.0, 0.5, and 0.1 ppm 2,4‐D. Pathologic lesions were seen in the fish; high‐treatment fish had earlier and more severe effects than did low‐treatment fish. The pathology involved liver, vascular system, and brain, with depletion of liver glycogen, globular deposits in the blood vessels, and stasis and engorgement of the circulatory system of the brain. Little pathology was seen after 84 days.