Insects ecdysteroids

Although phytosterols are converted into other sterols (such as cholesterol) that serve as components of membranes and in other functions, one of the principal reasons that insects require phytosterols is for conversion to ecdysteroids. Insects differ in their ability to utilize different phytosterols (Svoboda and Thompson, 1987). Although cholesterol (7) will satisfy this demand in most insects, most plants contain only traces of this sterol (Svoboda and Thompson, 1987). 

Insects, crustaceans, platehelminthes, nematodes and annelids use homoses-quiterpenoid epoxides (juvenile hormones) and ecdysteroids (ecdysone, 20-... 

Sehnal F, Bryant P J 1993 Delayed pupariation in Drosophila imaginal disc overgrowth mutants is associated with reduced ecdysteroid titer. J Insect Physiol 39 1051-1059... 

Another aspect of the sex pheromone communication system concerns the endogenous signals that control pheromone production and release from the emitting insect. A number of hormones have been found to be involved in the control of pheromone production in various insect species (18). Juvenile hormone was found to induce vitellogenesis and sex pheromone production in some cockroach and beetle species. However, ecdysteroids were found to be involved in regulating reproductive processes, including vitellogenin synthesis, in dipteran species. 

Ecdysteroids. Ecdysteroids can be isolated from many species of the annual kingdom that belong to the phyla Protomia, e.g., insects, worms, and arthropods, as well as a variety of different plant species. Ecdysteroids include the molting hormones, however, nnl all the over 60 ecdysteroids that have been isolated are active hormones. Ecdysteroids from animals... 

Juvenile hormone (JH) regulates both vitellogenesis and pheromone production in some insect species (Tillman et al., 1999). In some Diptera, including the housefly, ovarian-produced ecdysteroids are involved in regulating vitellogenesis (Hagedom, 1985 Adams et al., 1997) at the transcriptional level (Martin et al., 2001). Because ovariectomy abolished sex pheromone production while alletectomy (which abolishes JH production) had no effect on pheromone production (Blomquist et al., 1992), it was therefore hypothesized that an ecdysteroid, and not JH,... 

HE into ovariectomized insects over several days resulted in as much (Z)-9-tricosene produced as in intact control females. Application of JH or JH analogs alone or in combination with ecdysteroids had no effect on pheromone production, confirming that JH does not have a role in regulating housefly pheromone production (Blomquist et al 1992). 

Adams T. S., Gerst J. W. and Masler E. P. (1997) Regulation of ovarian ecdysteroid production in the housefly, Musca domestica. Arch. Insect Biochem. Physiol. 35,135-148. 

Blomquist G. J., Adams T. S., Halamkar P. P., Gu P., Mackay M. E. and Brown L. (1992) Ecdysteroid induction of sex pheromone biosynthesis in the housefly, Musca domestica. Are other factors involved J. Insect Physiol. 38, 309-318. 

Endocrine mediators, including specific pheromonotropins (e.g. pheromone biosynthesis activating neuropeptide [PBAN]) (reviewed in Raina, 1993 Nagasawa et al., 1994 Rafaeli, 2002 Rafaeli and Jurenka, Chapter 5, in this volume), JH (reviewed in Tillman et al., 1999), and ecdysteroids (reviewed in Blomquist et al., 1993 Blomquist, Chapter 8, in this volume), can regulate pheromone biosynthesis in different insect species. 

Blomquist, G.J. (2003). Ecdysteroid regulation of pheromone production in the housefly, Musca domestica. In Insect Pheromone Biochemistry and Molecular Biology, ed. G.J. Blomquist and R.G. Vogt. London Elsevier, pp. 231-252. 

Trabalon, M Pourie, G. and Hartmann, N. (1998). Relationships among cannibalism, contact signals, ovarian development and ecdysteroid levels in Tegenaria atrica (Araneae, Agelenidae). Insect Biochem. Mol. Biol., 28,751-758. 

Two main hypotheses have been put forward to account for the occurrence of ecdysteroids in the plant world. The first is that PEs have a hormonal role within the plant, but there is very little hard evidence in support of this hypothesis (reviewed in [26]). Alternatively, PEs participate in the defence of plants against non-adapted phytophagous invertebrates. Deterrent effects of 20E on non-adapted insect species are... 

Recently, it has been demonstrated that ecdysteroid accumulation in spinach is inducible by mechanical [50] or insect [51] damage to roots. Evidence was further provided for the involvement of jasmonates in the induction of de novo ecdysteroid synthesis. Also, short- and long-term labelling of 20E from [2-14C]mevalonic acid in spinach demonstrate that ecdysteroids are metabolically stable in this species, which fits much better with a role in plant defence, rather than a phytohormonal role [52], Most recently, it has been demonstrated that root predation by the fungus gnat Bradysia impatiens results in elevated ecdysteroid levels in spinach and a significant reduction in larval establishment of B. impatiens [53],... 

It has been recognised for some time that certain insect species have the ability to perceive ecdysteroids [38,116,117], This is probably a general phenomenon for many phytophagous insect species, which would encounter phytoecdysteroids in their diets [26], Only recently have more extensive electrophysiological studies on ecdysteroid taste receptor cells been performed [40,118], but very little is currently known about their specificity [119], This will clearly be an important area for future research, if ecdysteroids (or their analogues) are to be developed further as crop protection agents. 

Ecdysteroids are generally regarded as not being able to penetrate insect cuticle readily [179], However, the rice stem borer, C. suppressalis, has a thin cuticle which allows ecdysteroids to penetrate when ligated last instar larvae are dipped into a methanolic solution of the test compound for 5 s [180], The proportion of pupated abdomina are assessed after 48 h. This assay is less sensitive than the Calliphora bioassay, but is easier to perform. Its main application has been in screening plant extracts for the presence of phytoecdysteroids [74],... 

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