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Effects of 0.01, 0.1 and 1.0 ppm methoprene (Altosid®: ZR-515), a juvenile hormone (JH) mimic which shows high activity against some economically important insect pests, especially Diptera, were tested on larvae of the mud-crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae) from hatching to the first crab stage under optimum and stress conditions of a number of salinities and cyclic temperatures. There was a significant reduction in survival of zoeal larvae with increasing concentrations of methoprene in nearly all combinations of salinity and temperature. On the average there was 9% less survival in the 0.01 ppm concentration of methoprene than in the control, and in the 0.1 ppm concentration the survival was further reduced by another 16%. At 1.0 ppm methoprene no larvae survived beyond the first zoeal stage under optimum conditions or under stressful combinations of salinity and temperature. Except at 0.2 ppm in 27.5% S, survival of the megalopa was not significantly reduced in 0.01 or 0.1 ppm methoprene in any salinity or temperature, although the percentage of abnormal megalopa increased under stress conditions. The first zoeal stage was the most sensitive of the larval stages to methoprene as well as to salinity and temperature stress. The duration of zoeal development was significantly lengthened with an increase in concentration of methoprene under nearly all conditions of salinity and temperature. The JH mimic had, however, no significant effect on the duration of megalopa development. A significant synergism between methoprene, salinity and temperature was not observed. It can be concluded from the results that methoprene does not inhibit metamophosis of R. harrisii larvae at the 0.1 ppm level or lower. Reduction in survival of zoeal stages and increased duration of zoeal development with increasing concentrations of methoprene are presumably related to stress.

Laboratory experiments wer conducted to determine the effects of Kepone on the larval development of the mud-crab,Rhithropanopeus harrisii, and the commercial blue crab,Callinectes sapidus, from the time of hatching until the 1st crab stage was reached.

Survival of Rhithropanopeus harrisii larvae from hatching to first crab stage occurred in Na2CrO4 concentrations from 1.1 to 29.1 ppm. Estimated LC50 for complete zoeal development was 17.8 ppm Na2CrO4 and it was 13.7 ppm for development to first crab stage. A concentration of 1.1 ppm Na2CrO4 was nontoxic, while Na2CrO4 concentrations of 7.2 and 14.5 ppm were sublethal and concentrations of 29.1 to 58.1 ppm were acutely toxic. Low concentrations of Na2Cr04 caused an increase in swimming speed and high concentrations caused a decline.

Laboratory experiments were conducted to determine the effects of methoxychlor on the larval development of the mud-crab, Rhithropanopeus harrisii, and the commercial blue crab, Callinectes sapidus, from the time of hatching until the 1st crab stage was reached. The effect of a range of concentrations of methoxychlor on survival of larvae of C. sapidus and R. harrisii was determined, as well as the concentrations which were sublethal and lethal. Since concentrations as low as 1.3, 1.6 and 1.9 ppb (μg l−1) methoxychlor were acutely toxic to C. sapidus larvae, and it took a concentration as high as 7.0 ppb to be acutely toxic to R. harrisii larvae, it was concluded that C. sapidus larvae were much more sensitive to methoxychlor than R. harrisii larvae. Zoeal and total development to the 1st crab stage of R. harrisii and C. sapidus were prolonged in relation to increased concentrations of methoxychlor. The developmental stages in which larvae were particularly sensitive varied in the two species. Methoxychlor residues of R. harrisii and C. sapidus larvae reared in concentrations of methoxychlor were determined.

Effects of the juvenile hormone (JH) mimic hydroprene (Altozar®: ZR-512), which exhibits high activity against Lepidoptera, were studied on the larval development of the mud-crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae). Larvae reared in 20‰ S at 3 cycles of temperature of 20° to 25°C, 25° to 30°C and 30° to 35°C, were exposed to 0.01, 0.1 and 0.5 ppm hydroprene from hatching to the first crab stage. Larvae were also exposed to 0.1 and 0.5 ppm hydroprene only from the megalopa stage to the first crab stage. When larvae were treated with hydroprene throughout larval life, survival was significantly reduced with increasing concentrations of the compound at all temperature cycles. Synergistic effect between hydroprene and temperature on survival of zoeal larvae was not observed. On the average there was 11% less survival in the zoeal stages at the 0.01 ppm concentration. of hydroprene than in the control, an additional reduction of 13% occurred at 0.1 ppm, and finally there was a further decrease of 46% at 0.5 ppm hydroprene. Significant decrease in survival in the megalopa stage occurred only in the 0.5 ppm concentration of hydroprene at the lowest temperature cycle when larvae were exposed to the compound from hatching. When larvae were treated with hydroprene only within the megalopa stage, a significant reduction in survival was not observed. First-stage zoeae were the most sensitive of the larval stages to hydroprene. Duration of zoeal development was significantly delayed at 0.5 ppm hydroprene at the two lower temperature cycles, whereas in the megalopa stage the delay began at the 0.1 ppm level at all 3 temperature cycles when larvae were exposed to hydroprene from hatching. A significant delay was also observed at 0.1 ppm hydroprene at the two lower cycles when larvae were exposed to hydroprene only in the megalopa stage; at 30° to 35°C a significant delay was observed only at the 0.5 ppm level. The results show that metamorphosis to the first crab stage was not inhibited at the 0.5 ppm level of hydroprene or lower. Reduction in survival and increase in duration of larval development were presumably related to stress conditions caused by hydroprene. The results also suggest an interaction between temperature and hydroprene on survival of megalopa larvae and duration of larval development.

The mud aqueous fraction (MAF) and suspended particulate phase (SPP) of low-density lignosulfonate type mud with uerrochrome added were nontoxic to larvae during the complete larval development of Rhithropanopeus harrisii. Five percent (5000 ppm, 0.5 % v/v mud in water) MAF and SPP were not toxic to Callinectes sapidus. Survival of C. sapidus larvae decreased as concentrations of MAF and SPP increased from 5 % (5000 ppm, 0.5 v/v mud in water) to 50% (50000 ppm, 5 % v/v mud in water). No larvae reached the 1st crab stage in 100% (100000 ppm, 10% v/v mud in water) MAF and SPP. Statistical analysis of the data on survival, mortality, and behavior are presented.

Effects of Dimilin® (TH 6040), an insect growth regulator which interferes with the formation of the insect cuticle, were studied on the larval development of Rhithropanopeus harrisii (Gould) and Sesarma reticulatum (Say) (Crustacea: Brachyura). When larvae were exposed to 0.5 (R. harrisii only), 1, 3, 5, 7, and 10 ppb Dimilin from hatching to the first crab stage, survival in both species decreased in relation to increased concentrations of Dimilin. Survival of R. harrisii larvae wa significantly lower at 1 ppb and higher levels compared with control experiments, and in S. reticulatum a significant decrease in survival began at the 3 ppb level. At 10 ppb Dimilin, no larvae survived to the megalopa stage in either of the two species. The results indicate that early stage larvae of R. harrisii are more sensitive to Dimilin than those of S. reticulatum. When R. harrisii larvae were treated with 10 ppb Dimilin during the intermolt period of each of the 4 zoeal stages, nearly all larvae died during molting to the succeeding stage. First zoeal larvae of R. harrisii exposed to 10 ppb Dimilin at various days during the intermolt period were more sensitive to the compound late than early in the period. It is suggested that Dimilin also may interfere with the formation of the cuticle in crab larvae.

LITT LE is known of the influence of physical factors on the complete larval development of Xanthid crabs. In reports on the successful rearing of the larvae in the laboratory, data on salinity and temperature are either omitted (Hart, 1935; Knudsen, 1958) or, when given, are limited in range (Chamberlain, 1957). Connolly (1925) mentions that the larvae of Rhithropanopeus harrisi were obtained from waters of different salinity but does not give the hydrographic data for the collecting stations. Bousfield (1955), concerned primarily with distribution of barnacle nauplii in the Miramichi Estuary, does indicate the range of salinity in which he found adults and zoeae of R. harrisi. Studies on the development of the Xanthidae have been primarily confined to descriptions of larval stages based on reconstructions from the plankton (Birge, 1883, Neopanope texana sayi; Hyman, 1925, N. texana sayi, Panopeus herbstii, Eurypanopeus depressus and a few stages of other Xanthids; Connolly, 1925, R. harrisi). More recently the larvae of some species of this family have been reared successfully in the laboratory (Hart, 1935, Lophopanopeus bellus; Chamberlain, 1957, N. texana sayi; Knudsen, 1958, 1959a, 1959b, L. leucomanus leucomanus, L. bellus diegensis, Paraxanthias taylori; and Costlow and Bookhout, 1961a, E. depressus, and 1961b, P. herbstii).