megalop stage was reduced in concentrations ot 0.01 ppm and 0.0001 
methoprene, but there was no significant effect on the survival lor 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. There 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 with 5 ppt or 35 ppt (Costlow, 1977). 
Christiansen, 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 concentration 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 third compound, MONO-585, 
affected the response of larvae of R. harrisii to light, indicated that both 
swimming 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 of 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 with 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. 
332 
