Marit E. Christiansen

The effect of salinity and cyclic temperature on larval development of the mud-crab Rhithropanopeus harrisii (Brachyura: Xanthidae) reared in the laboratory

Larvae of Rhithropanopeus harrisii (Gould) were reared from hatching to the first or second crab stages in 11 combinations of salinities and cyclic temperatures (5, 20, and 35‰ S at 20° to 25°C, 25° to 30°C, and 30° to 35°C; 25‰ S at 20° to 25°C and 30° to 35°C). The larvae survived to the megalops and first crab stages in all salinities and cycles of temperature other than 5‰ S at 30° to 35°C. The best survival to the megalops (94%) and first crab (90%) stages occurred in 20‰ S, 20° to 25°C. In all other combinations of salinities and temperatures there was a reduction in survival to the first crab stage. The duration of the larval stages was affected significantly by temperature, whereas the effect of salinity on the mean days from hatching to the first crab stage was not consistent at the different temperature cycles. Development to the first crab stage required the shortest time in 20‰ S, 30° to 35°C (mean 12.3 days), and the longest time in 5‰ and 35‰ S, 20° to 25°C (mean 22.6 days and 21.6 days, respectively). Megalops larvae reared in 35‰ S at all cycles of temperature, as well as larvae in 20‰ and 25‰ S, 30° to 35°C, showed a high percentage of abnormality, with the highest percentage occurring in 35‰ S, 30° to 35°C. It appears that larval development of R. harrisii is strongly influenced by environmental factors and not solely related to genetic differences.

Effects of the juvenile hormone mimic ZR-515 (Altosid®) on larval development of the mud-crab Rhithropanopeus harrisii in various salinities and cyclic temperatures

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.

Effects of the insect growth regulator Dimilin® (TH 6040) on larval development of two estuarine crabs

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.

Effects of the juvenile hormone mimic ZR-512 (Altozar®) on larval development of the mud-crab Rhithropanopeus harrisii at various cyclic temperatures

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.

Ultrastructural study of the exoskeleton of the estuarine crab Rhithropanopeus harrisii: Effect of the insect growth regulator Dimilin® (diflubenzuron) on the formation of the larval cuticle

Ultrastructure of larval cuticle during the molt cycle of the estuarine crab Rhitropanopeus harrisii (Gould) (Crustacea: Brachyura) was studied in control larvae as well as in larvae exposed to 10 ppb of the insect growth regulator Dimilin® (diflubenzuron). First zoeal larvae were used as test organisms. It has earlier been shown that 10 ppb Dimilin is lethal to zoeal larvae of R. harrisii, and nearly all exposed larvae died during molting to the next stage (Christiansen et al., 1978). Distinct differences in structure of the cuticle were found between the two groups of larvae. Both endocuticle and exocuticle appear to be deformed in Dimilin-treated larvae, whereas formation of epicuticle did not seem to be affected. The results indicate that Dimilin probably inhibits chitin synthesis in crab larvae as shown earlier by several authors for insect larvae.

Feeding experiments on the larvae of the fiddler crab Uca pugilator (Brachyura, Ocypodidae), reared in the laboratory

Abstract Larvae of Uca pugilator (Bosc) were reared in the laboratory from hatching to the megalopa stage on three different diets: (1) newly hatched Artemia salina nauplii (diet A), (2) the rotifer Brachionus plicatilis (O.F. Muller) and a ciliate Euplotes sp. (diet RC), and (3) a combination of the above two diets (diet ARC). The survival rate of zoeae fed diet A (90.0%) and diet ARC (93.8%) was much higher than that of the larvae fed diet RC (22.5%). The duration of the zoeal stages was significantly shorter for the larvae fed diet ARC than for those fed diets A and RC. The survival rate of megalopa larvae (reared on diets A and ARC in the zoeal stages) was high (above 90%) for megalopa fed Artemia nauplii only, as well as for those fed a combination of Artemia nauplii and shrimp. No significant differences in duration of the megalopa stage were found between the latter diet groups.

Effect of the insect growth regulator diflubenzuron (Dimilin®) on the uptake of glucose and N-acetylglucosamine into the cuticle of crab larvae

Incorporation of 3H-labelled glucose and 3H-labelled N-acetylglucosamine (NAGA) — both precursors to chitin —into the cuticle of Rhithropanopeus harrisii (Gould) larvae (Crustacea: Brachyura) has been examined at different stages of the moult cycle in control larvae as well as in larvae treated with the insect growth regulator diflubenzuron (Dimilin®). As far as the control larvae were concerned, the incorporation of both precursors was high at the postmoult stage when endocuticle was secreted. NAGA appeared to be a more specific precursor of cuticular material than glucose during the premoult stage when exocuticle was produced. Incorporation of both precursors was low immediately before ecdysis and during the intermoult stage when secretion of the cuticle is complete. The results show that incorporation of glucose into chitin was greatly inhibited by the pollutant during the postmoult stage when endocuticle is produced, while incorporation of NAGA was reduced to a lesser extent at this stage. Diflubenzuron treatment markedly affected the incorporation of both NAGA and glucose in the premoult stage during secretion of exocuticle.

Larval Development of Hy as Araneus (Linnaeus) With and Without Antibiotics (Decapoda, Brachyura, Majidae) 1)

[Die Larven von Hyas araneus (Linnaeus) wurden im Laboratorium aufgezogen, und zwar vom Schlupfen bis zum ersten Krabbenstadium. Die vollstandige Larvenentwicklung umfasst ein Prezoea-Stadium, zwei Zoea-Stadien und ein Megalopa-Stadium. Die Larven wurden bei 10°, 15° und 20°C gehalten. Kulturen, denen man Antibiotica (50 I.E. Penicillin/0,05 mg Streptomycin pro ml) zugesetzt hatte, wurden mit Kulturen, denen man keine Anti-biotica zugesetzt hatte, verglichen. Bei 10°C und 15°C hauteten sich 73% der Larven, denen Antibiotica zugesetzt worden waren, bis zum Megalopa-Stadium; wahrend sich bei der gleichen Temperatur keine der Larven, die ohne Antibiotica behandelt worden waren, bis zu diesem Stadium sich hauteten. Bei 20°C (21,5-22°C) hauteten sich jedoch keine der Larven bis zum Zoea 2-Stadium, ob sie nun mit oder ohne Antibiotica behandelt worden waren. Die Entwicklung bis zum Megalopa-Stadium dauerte im Durchschnitt 37,8 Tage bei einer Temperatur von 10°C, und 27,8 Tage bei einer Temperatur von 15°C. Die Entwicklung bis zum ersten Krabbenstadium umfasst, bei einer Temperatur von 10°C, 65 Tage, und bei einer Temperatur von 15°C, 52 Tage. Die Morphologie der Larven wird spater publiziert werden., Die Larven von Hyas araneus (Linnaeus) wurden im Laboratorium aufgezogen, und zwar vom Schlupfen bis zum ersten Krabbenstadium. Die vollstandige Larvenentwicklung umfasst ein Prezoea-Stadium, zwei Zoea-Stadien und ein Megalopa-Stadium. Die Larven wurden bei 10°, 15° und 20°C gehalten. Kulturen, denen man Antibiotica (50 I.E. Penicillin/0,05 mg Streptomycin pro ml) zugesetzt hatte, wurden mit Kulturen, denen man keine Anti-biotica zugesetzt hatte, verglichen. Bei 10°C und 15°C hauteten sich 73% der Larven, denen Antibiotica zugesetzt worden waren, bis zum Megalopa-Stadium; wahrend sich bei der gleichen Temperatur keine der Larven, die ohne Antibiotica behandelt worden waren, bis zu diesem Stadium sich hauteten. Bei 20°C (21,5-22°C) hauteten sich jedoch keine der Larven bis zum Zoea 2-Stadium, ob sie nun mit oder ohne Antibiotica behandelt worden waren. Die Entwicklung bis zum Megalopa-Stadium dauerte im Durchschnitt 37,8 Tage bei einer Temperatur von 10°C, und 27,8 Tage bei einer Temperatur von 15°C. Die Entwicklung bis zum ersten Krabbenstadium umfasst, bei einer Temperatur von 10°C, 65 Tage, und bei einer Temperatur von 15°C, 52 Tage. Die Morphologie der Larven wird spater publiziert werden.]

First record of the thalassinid Callianassa subterranea (Montagu) (Crustacea, Decapoda) from the coast of Norway

A small specimen of Callianassa subterranea has been found on the south coast of Norway between 60 and 100 m depth. This is the first published record of the species from the Norwegian coast.

Effect of Diflubenzuron on the Cuticle of Crab Larvae

During the last few years the chitin synthesis inhibitor diflubenzuron (DimilinR, TH 6040) [l-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)-urea] has been used for the control of a few insect pests. Marx (1) indicated that inhibitors of chitin synthesis might not be totally specific for insect pests, but could also affect other arthropods including such economically important crustaceans as crayfish, crab, lobster and shrimp.