Ecdysis effects

Weis, J.S. 1976. Effects of mercury, cadmium, and lead salts on regeneration and ecdysis in the fiddler crab, Uca pugilator. U.S. Natl. Mar. Fish. Serv., Fish. Bull. 74 464-467. 

Larvae of Inoplnatus emerge as major sequestrators of cardenolides primarily because their hemolymph, which is present in a relatively large volume, effectively sequesters high concentrations of polar cardenolides (26). Cardenolide excretion largely reflects loss of these steroids as components of the larval exuviae, the concentration of these compounds becoming relatively stable after pupal ecdysis. These steroids are ubiquitously distributed in the adult moth, having been derived primarily from the rich cardenolide pool in the larval blood. 

Ecdysone stimulates the synthesis of RNA in tissues. Visual demonstration of the effect is provided by its action on polytene chromosomes of fly larvae (Fig. 26-14).361 Fifteen minutes after the application of ecdysone, a puff is induced on one band of the chromosome a second puff forms at a later time while a preexisting puff diminishes. Thus, like steroid hormones in mammals, ecdysone appears to have a direct controlling effect on transcription. The cuticle-shedding process (ecdysis) is initiated by the brain peptide eclosian. However, the brain may be responding to the ecdysis-triggeiing hormone, a peptide that is secreted by a series of epitracheal glands located in various segments of the body.362... 

Buprofezin / A, / S (Cyclic urea) ) N NC(CH,j)3 N 0 CH(CHj)2 Probable chitin synthesis and prostaglandin inhibitor. Hormone disturbing effect, leading to suppression of ecdysis... 

Explanation In many lepidopterans, including T. ni, the presence of JH in the prepupa seems to accelerate the time of ecdysis to the pupa (18,35-38). Conversely, a reduction in the JH titer due to an AJH causes a delay in the time of ecdysis to the pupae and/or the tanning process (18,37). This particular effect can be prevented, in part, by the coapplication of JH I (18). Thus, a delay in the time of tanning/pupation seems to be related to the ability of a compound to block JH biosynthesis/release or action, and hence act as an AJH. 

One hypothesis on themecKanlsm of action of JH In the Inhibition of ecdysis Implicates the active role of JH In the regulation of ecdysone tltres In the Insect body (17), possibly a consequence of an effect on the prothoradc glands (22). Another hypothesis Implicates an effect of JH on ecloslon hormone or Its action (20, 18). 

Acetylation of the hydroxyl group at C-5 of plumbagln had no effect on the biological activity. However, elongation of the ester group at this position resulted In a loss of ecdysis inhibitory activity. Thus, plumbagln and its acetate were more potent In our bloassays than were the synthetic analogs (32). 

Our present meagre understanding of normal endocrine processes in invertebrates makes the assessment of chemical endocrine disruption in the field difficult (LeBlanc 1999). Steroid roles differ between species and sometimes sexes, and their influence may vary at different developmental stages. In most studies of invertebrates, endocrine disruption appears to involve androgenization rather than oestrogenic effects (see Box 7.2). Arthropods (crustaceans and insects), annelids and molluscs use ecdysteroids, terpenoids and vertebratelike sex steroids for endocrine control. For example, the ecdysteroid ecdysone is naturally converted to 20-hydroxyecdysone (Fig. 7.10), which induces moulting (ecdysis) in both insect larvae and crustaceans. 

Ecdysone induces the larval-pupal metamorphosis in the absence of JH or a JH-active insecticide, but the presence of active compounds leads to a new larval stage at ecdysis, or to the development of larval-nymphal, larval-pupal, or larval-adult intermediates that are unable to give rise to normal adults. Treated pupae (e.g., tobacco cutworms treated with pyriproxyfen) may develop into normal adults. However, the females are unable to deposit eggs because a substance that induces oviposition behavior after mating is not released in the hemolymph. Other physiological and behavioral effects of JH-active insecticides are also observed. 

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