Once the megalopa have metamorphosed to juvenile crabs, there is no 

 significant effect on survival during the subsequent four juvenile molts due to 

 eitlier 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 sapidiis 

 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, tliree, 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 a/ (13) found that hydroprene (Altozar ) caused 

 premature metamorphosis of larvae of the barnacle B. galeatus while a second 

 mimic, methoprene (Altosid ) had no effect on the time of metamorphosis, 

 nor did it prevent settling when a proper substrate was available. 



Two other analogs, farnesyl methyl etlier (FME) and ethyl, 10, 1 l-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 oi 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 ) on larvae of the estuarine mudcrab, 

 Rhithropanopeus hanisii (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 v^thin the 



329 



