イノコステロン投与によるクルマエビの脱皮促進について

抄録

Recent finding and isolation of an insect molt-inducing hormone, the inokosterone, from the root of plants, Achyranthes, let the present author to carry out experiments to examine its effectiveness on crustaceans. The inokosterone solution was made up from 5.1mg crystal with 0.2ml of ethanol and 49.9ml of sterilized re-distilled water, and was injected into abdominal muscles of young P. japonicus (2.8-15.5g in body weight) by means of a tuberculin syringe at various time lapses after the first molt in the experimental aquaria. Molt inducing effect was examined by the length of time between the first and the second molt.
A single injection of 0.03ml of the solution, which contained 3μg of inokosterone, per gram of live weight of the shrimp gave a remarkable molt-inducing effect. In the uninjected shrimps, or those injected with the comparable amount of sterilized re-distilled water (controls), intervals between molts varied from 9-16 days at the experimental temperature (25-27°C) depending on the body weight. Statistical treatment revealed that the interval between molts was increased by 0.8 day for every 1g increase in body weight. While, in the inokosterone injected shrimps intervals between molts no longer depended on body weight, but on the stage of molting cycle in which the inokosterone was injected. The intervals averaged 2.4 days for 6 shrimps which were injected on 0.5-1.5 days (stage B) after the first molt, and 7.0 days for 11 shrimps which were injected on 2.5-5.5 days (stage C) after the first molt. Thus the inokosterone injection during stages B or C markedly accerelated the molting cycle resulting in a precocious ecdysis on average of 3.3 days after the injection. When the shrimps were already in premolt condition (stage D) at the time of injection, molting occurred in less than 3 days (Fig. 3). Since the reaction time was too short to be in normal molting cycle it was postulated that the inokosterone may had a direct influence on the epidermis.
Out of 29 inokosterone injected shrimps, 16 shrimps died during or just after the second molt. In 4 shrimps exuviations were incomplete, some parts of old exoskeleton, head or the posterior parts of abdomen, remained unmolted. Only 9 shrimps passed the successful second molt. While, in the controls as well as in uninjected shrimps second molts were always successful.
Weight increases after the second molt were significantly less in the inokosterone injected shrimps, which had passed the successful molt, than in the controls or uninjected shrimps of comparable size.