hormone mimics or analogs, are intended to simulate the activity of naturally 
occurring juvenile hormones and prevent metamorphosis or, in the case of a 
second group, insect growth regulators, to control differentiation or specific 
physiological processes during development. 
Several authors have reported the effects of juvenile hormone mimics on the 
development of insects (15, 17, 19 and others). Only a few studies, however, 
are reported on the effects of these compounds on other invertebrates (9, 10, 
13). Of these Gomez et al (9) and Ramenofsky et al (13) first described the 
effect of two juvenile hormone mimics on development and metamorphosis of 
the cirripede, Balanus galeatus, and Tighe-Ford (1977) subsequently reported 
juvenile hormone analog effects on another species of barnacle, Elminius 
modestus. Studies on representative species of other marine Crustacea are 
limited, but do include the effect of two juvenile hormone mimics on larval 
development of the mud-crab, Rhithropanopeus harrisii (1, 2, 4). A study by 
Forward and Costlow (8) describes the manner in which one of these 
compounds may affect the behavior of crab larvae. Pa yen and Costlow (11) 
studied the effects of juvenile hormone mimics on gametogenesis of adult 
Rhithropanopeus harrisii. 
Because of the phylogenetic relationships between insects and crustaceans, 
one might legitimately expect that those compounds which would alter or 
interfere with the developmental pattern of insects could also have similar 
effects during the development of marine decapods. 
The present study was undertaken to further explore the effects of two 
compounds, methoprene (Zoecon Corporation) and MONO-585 (Monsanto 
Corporation) on the development of larvae of estuarine crabs. Specifically, 
experiments were designed to determine if these compounds would affect 
survival of the larvae, alter the number of larval stages, change the time 
required for development of all stages and metamorphosis, or affect the 
frequency of molting within the early juvenile crab stages after metamorphosis. 
A second portion of the experiment was designed to determine if effects of 
these compounds would be altered by changes in such environmental factors as 
salinity and temperature. 
The two species which were selected for study were the small mud-crab, 
Rhithropanopeus harrisii (Gould), and the megalopa of the commercial blue 
crab, Callinectes sapidus Rathbun. 
MATERIALS AND METHODS 
Following the general rearing procedures described by Costlow and 
Bookhout (5) and Costlow, Bookhout and Monroe (7) ovigerous females of C 
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