megalopa stage was reduced in concentrations of 0.01 ppm and 0.0001. 

 methoprene, but there was no significant effect on the survival for larvae 

 maintained in higher salinities. The developmental time was not significantly 

 altered by the two lower concentrations of the compound and super-numerary 

 larval stages were not observed in any of the experimental series. Tliere was 

 evidence that the early megalopa stage represented a period of extreme 

 sensitivity to environmental stress in any form, including the presence of 0.1 

 ppm methoprene when combined v^th 5 ppt or 35 ppt (Costlow, 1977). 



Chrisfiansen, Costlow, and Monroe (1) reported a significant reduction in 

 survival of zoeal larvae of Rhithropanopeus harrisii with increasing 

 concentrations of methoprene (Altosid^: ZR-515) and further observed an 

 increase in the duration of zoeal stages as the concentrafion of methoprene was 

 increased, irrespective of changes in temperature or salinity. Below 0.1 ppm, 

 methoprene did not inhibit metamorphosis. The work with a second 

 compound, hydroprene (Altozar^: ZR-512) also resulted in a significant 

 reduction of survival of larvae of Rhithropanopeus harrisii, and the first stage 

 larvae appear to be the most sensitive stage within the four zoeae and one 

 megalopa. Metamorphosis to the first crab stage was not inhibited at 

 concentrations of 0.5 ppm or lower. 



An additional study on the way in which a tliird compound, MONO-585, 

 affected the response of larvae of R, harrisii to light, indicated that both 

 shimming speed and phototaxis were altered by the presence of this compound 

 at sublethal concentrations (8). Further information on how this general group 

 of compounds may affect a variety of physiological and developmental 

 processes in marine crustacean larvae, however, is needed to determine if the 

 effects observed by previous authors are limited to the relatively few 

 compounds and few species which have heretofore been studied. 



From the present study it would appear that the compound MONO-585 is 

 not as toxic as methoprene. Although at the concentration of 10 ppm, 

 MONO-585 was lethal to larval stages of R. harrisii at salinities 5, 20 and 35 

 ppt, 1 ppm of this compound was only lethal when it was combined with a 

 salinity known to represent a stress condition to the developing larval stages (5 

 ppt). In similar studies on the effect of methoprene on the development o{ R. 

 harrisii (4) concentrations of 0.01 ppm and 0.0001 ppm methoprene resulted 

 in a reduction in survival of larvae at a salinity of 5 ppt but did not 

 significantly affect survival of larvae maintained in the higher salinities. A 

 concentration of 0.1 ppm MONO-585 had no obvious effect on survival in any 

 of the experimental salinities. As viith experiments on methoprene, duration of 

 the four zoeal stages and one megalopa of R. harrisii was not affected by the 

 lower concentrations of MONO-585. 



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