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 inortaHty 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 7?, 

 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 oi Callinectes sapidus, the only obvious effect on survival 

 in three cycles of ' temperature combined vdth 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 sahnity 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 Uttle information is available on the way in which early juvenile stages 

 of any crab respond to natural environmental conditions or artificial 

 compounds wliich 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 thejuvenile hormone mimics and 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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