Once the megalopa have metamorphosed to juvenile crabs, there is no 
significant effect on survival during the subsequent four juvenile molts due to 
either salinity or the presence of 1.0 ppm or 0.1 ppm MONO-585 (Figure 
21-6). The time required to complete the individual molts (first crab to second 
crab, second crab to third crab, third crab to fourth crab, and fourth crab to 
fifth crab) varies considerably in all experimental series (Figure 21-6). As might 
be expected, these same intervals were considerably reduced when the 
megalopa and juvenile crabs were maintained in the cyclic temperatures of 
25-30°C and 30-35°C (Figure 21-6). 
Effect of Methoprene on Development 
Neither the megalopa nor the early juvenile crabs of C. sapidus 
demonstrated significant changes in survival when exposed to 0.1 or 0.01 ppm 
dilutions of methoprene combined with salinities of 15, 25 and 35 ppt, and 
maintained in cyclic temperatures of 25-30°C or 30-35°C (Figure 21-7). In the 
reduced temperature cycle of 20-25°C, however, survival was reduced from 
20- 25 percent in the presence of 0.1 ppm methoprene, in all salinities. Juvenile 
crab stages, one, two, three, and four, however, did not show any reduction in 
survival when maintained in these same combinations. In the same 
combinations of cyclic temperature, salinity, and methoprene, there is no 
apparent change in time required for completion of the megalopa stage or in 
the interval periods observed for the first and subsequent crab stages (Figure 
21 - 8 ). 
DISCUSSION 
The relatively few studies to date on the effect of insect growth regulators 
on marine Crustacea have demonstrated that one may expect a variety of 
effects, depending upon the species and the chemical compound itself. Gomez 
et al (9) and Ramenofsky et al ( 13) found that hydroprene (Altozar R ) caused 
premature metamorphosis of larvae of the barnacle B. galeatus while a second 
mimic, methoprene (Altosid R ) had no effect on the time of metamorphosis, 
nor did it prevent settling when a proper substrate was available. 
Two other analogs, farnesyl methyl ether (FME) and ethyl, 10, 11-epoxy-3, 
7, 10, 1 l-tetramethyl-2-cis-trans-6-cis-trans-dodeca-dienoate (Ro-8-4314) were 
shown by Tighe-Ford (1977) to interfere with the development of Elminius 
modestus larvae, with the effect apparently related to the state of physiological 
development of larvae at the time of exposure. Costlow (4) described the 
effects of methoprene (Altosid R ) on larvae of the estuarine mudcrab, 
Rhi thro panop eus harrisii (Gould) and indicated that 1.0 ppm resulted in total 
mortality of the larval stages, usually within the First two days of hatching. If 
the larvae were maintained in salinities as low as 5 ppt, survival within the 
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