Previous studies on survival and length of life of megalopa of Callinectes 
sapidus (3) have indicated that they will withstand a wide range of salinity and 
temperature and display remarkably uniform survival in all but the lower 
salinities (5-10 ppt). In the present experiment, survival of the control series at 
20 and 35 ppt was similar to that recorded for previous studies, but the 
reduction in survival of the 10 ppm and 1 ppm MONO-585 clearly indicate the 
toxicity of this compound to the late larval stages of the commercial crab 
(Figure 21-3). Total mortality was observed when the larvae were exposed to 
10 ppm regardless of the salinity, and at 1 ppm, survival was reduced to 
approximately 40 percent, while survival at 0.1 ppm resulted in a slight 
reduction in survival relative to the control series (Figure 21-3). As with R. 
harrisii (4), there was no significant reduction in time required for 
metamorphosis, regardless of the concentration of MONO-585 (Figure 21-4). 
Earlier studies on the effect of cyclic temperatures, as opposed to constant 
temperatures, on the survival of larvae of the mud-crab Rhithropanopeus 
harrisii (6, 16) indicated that at one particular five degree cycle of temperature, 
30-35°C, a significantly higher survival could be expected relative to that 
observed in a constant temperature of either 30°C or 35°C. In the present 
study with megalopa of Callinectes sapidus , the only obvious effect on survival 
in three cycles of temperature combined with three salinities and two 
concentrations of MONO-585, was also associated with the high cycle of 
temperature, 30-35°C (Figure 21-5). Although there was no significant 
reduction in survival at 15 or 25 ppt combined with 1.0 ppm MONO-585, 
megalopa maintained in a salinity of 35 ppt, 1.0 ppm MONO-585, showed a 
significant reduction in survival at a cycle of 20-25°C and at 25-30°C. When 
the megalopa were maintained at 1.0 ppm MONO-585, 30-35°C, survival was 
considerably increased but, as with the study on larvae of R. harrisii , there is at 
present no obvious explanation as to how this high cycle of temperature 
contributes to an increase in survival of the larval stages. 
Very little information is available on the way in which early juvenile stages 
of any crab respond to natural environmental conditions or artificial 
compounds which may be present within the water. From the present study it 
would appear that the intermolt period for the first four juvenile crabs may 
exhibit considerable variability, but this variability cannot be attributed to 
either salinity, temperature, or insofar as this experiment is concenrned, the 
presence of sublethal concentrations of either MONO-585 or methoprene 
(Figures 21-5 and 21-7). 
A broad range of questions remains concerning the physiological response of 
many crustacean larvae and adults to the juvenile hormone mimics in insect 
growth regulators. Nothing is known as yet as to how these compounds may be 
incorporated within the animal, or the way in which they may further alter 
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