eggs at 2.4 ppm, the only concentration used. Order of toxicity of 

 weedicides to clam larvae was the same as for egg development. Larvae grew 

 better in each of 4 concentrations of fenuron than in controls. Monuron at 

 low concentrations also increased growth of larvae but showed some toxicity 

 at 1 ppm and up. Diuron did not seriously interfere with growth at 1 ppm 

 and lower, but at 5 ppm drastically reduced growth and increased mortality. 

 Neburon at 2 . 4 and 4.8 ppm caused 100% larval mortality. Two oils, 

 orthodichlorobenzene and trichlorobenzene, are relatively insoluble in water 

 and were comparatively harmless to clam larvae at concentrations tested. 

 The first compound had no effect on egg development at concentrations less 

 than 10 ppm.. The second reduced the percentage of clam eggs developing 

 normally, but even at 10 ppm over 50% of eggs did develop normally. The 

 percentage of eggs developing normally was not affected by concentrations 

 of acetone as high as 100 ppm, but 1 ppm of allyl alcohol caused about 50% 

 reduction in number of eggs developing normally and completely prevented 

 normal development at 2.5 ppm. The difference in effect of these solvents 

 was even greater with clam larvae. Even 0.25 ppm of allyl alcohol killed 

 all larvae within 8 days, but survival was not affected by 250 ppm acetone, 

 and growth only slightly retarded. In tests with nemagon and sevin, results 

 were the same whether stock solutions were made up in water or acetone . 

 The insecticides guthion, sevin, lindane, toxaphene, aldrin, dicapthon, and 

 Niagara Compound N-3 514 were tested on clam eggs and larvae. Lindane was 

 the least toxic. About 60% of clam eggs developed normally in concentrations 

 up to 10 ppm, and no appreciable mortality of clam larvae occurred at this 

 concentration, which is essentially a saturated solution, but larval growth 

 was reduced. At 5 ppm and lower, lindane had no effect on survival or 

 growth of clam larvae. At 10 ppm aldrin, 64% of clam eggs developed 

 normally, but growth of larvae almost completely stopped at 0.25 and 0.5 

 ppm, although there was no mortality. At all higher concentrations of aldrin 

 mortality was 100%. Toxaphene also was more toxic to clam larvae than eggs. 

 Guthion was more toxic than sevin to clam eggs , but effects of the two on 

 larvae were about the same. Dicapthon was about as toxic as guthion and 

 sevin to clam eggs, but somewhat more toxic to larvae. Niagara Compound 

 N-3514 (2-chloro-l-nitropropane) was most lethal of all insecticides tested 

 to clam eggs and larvae. Concentrations as low as 1 ppm caused total 

 mortality. With almost every compound tested, slowing of larval growth 

 rate was the first evidence of toxicity. - J.L.M. 



437 



Davis, Harry C. 1962. 



Effects of some pesticides on eggs and larvae of oysters (Crassostrea 

 virginica) and clams (Mercenaria mercenaria) . Proc. Natl. Shellf. Assn. 51, 

 August 1960: iii. 



Listed by title only. - J.L.M. 



438 



Davis, Harry C. 1963. 



The effect of salinity on the temperature tolerance of eggs and larvae of 

 some lamellibranch mollusks. Proc. 16th Internatl. Congr. Zool., Vol. 1. 

 John A. Moore (edj : 226 (abstract) . 



A study of the effect of temperature on survival and growth of larvae of 

 hard clam, Mercenaria mercenaria, has shown that rate of growth at different 

 temperatures was critically affected by the type of food organisms available. 

 Clam and oyster larvae were able to use naked chrysophytes such as Mono- 

 chrysis lutheri, Isochrysis galbana, and Dicrateria sp., and show significant 

 growth, at lower temperatures than those at which chlorophytes, such as 

 Chlorella sp., which have cell walls, could be utilized. This implies that 

 the enzyme systems that digest naked flagellates are active at lower tempera- 

 tures than enzyme . systems required to digest cell walls. Cells of I. galbana 

 and M. lutheri are destroyed by temperatures of 27.5 to 30 °C and growth of 

 larvae receiving these foods at such temperatures is reduced. Chlorella sp. 

 can tolerate temperatures of 33°C and the rate of growth of larvae receiving 

 Chlorella sp. continues to increase with each 2.5°C increase in temperature 

 up to 33°C. Temperature tolerance of clam and oyster larvae is also signif- 



122 



