Ecdysones source

At the physiological level it is well established that vital dyes such as nile blue, neutral red and methylene blue retard larval development under normal lighting conditions (12L/12D with source unspecified) (25 27). Female but not male pupal weights are also reduced. Unfortunately experiments were conducted without dark controls so that it is difficult to evaluate the role of photosensitization in these effects. As house flies and fire ants succumb to photosensitization, they lose motor control and become more excitable (28). This suggested a neurotoxic effect and investigation of fire ant acetylcholinesterase vitro revealed that this enzyme was sensitive to photo-oxidation. vivo results, however, revealed no effect on the enzyme which suggests another mode of action. Epoxldatlon of cholesterol and membrane lysis may be alternative primary sites. If this were the case ecdysone metabolism of insects would probably also be effected. 

PE-free callus from Polypodium vulgare was shown to biotransform ecdysone fo 20-hydroxyecdysone, which is the last step in the biosynthetic pathway of the main plant PE. This hydroxylation is catalysed by a cytochrome P450 enzyme which was subsequently purified from that source (Canals et al, 2005). In another study, Reixach et al. (1999) have shown that 25-deoxy-20-hydroxyecdysone was transformed efficiently in both tissues into 20-hydroxyecdysone, but no 25-deoxyecdysteroids such as pterosterone and inokosterone were formed. Likewise, incubation of 2-deoxyecdysone produced exclusively ecdysone and 20E, indicating a high 2-hydroxylase activity in both tissues. 

The formation of phosphate esters of ecdysteroids constitutes a potentially valuable mechanism for storing high titers of insect steroids in a form that is inactive but that provides a readily available source of the active ecdysteroid. Embryos of . gregaria contain a phosphatase that can hydrolyze ecdysone 22-phosphate (36) and this enzyme could effect the controlled release of ecdysone and possibly other ecdysteroids at appropriate stages of insect development. 

It is not too surprising that many plants produce ecdysteroids to defend themselves against potential insect pests. The so-called phyto-ecdysones have a potent molt-inducing effect, and some of them may be even more potent than p-ecdysone. Gymnosperms and ferns often contain much of phyto-ecdysones. Bracken (Pteridium aquilium) and the rhizomes of the well-known liquorice fern (Polypodium vulgare), for instance, have up to 1% of their dry weight of p-ecdysone, and the rhizomes of liquorice can be used as a commercial source of P-ecdysones. A Siberian medicinal plant (Leuzea carthamoides) was recently studied by Zeleny et al. (1997). The plant has as... 

The main types of insect-specific hormone are a-ecdysone, from the pro-thoracic glands, which causes moulting the brain hormone that stimulates the pro thoracic glands and the juvenile hormone, in the corpora allata, which causes metamorphosis. Further, the corpus cardiacum releases a hormone that increases the amplitude of the muscles of heart and gut, and also an adipo-kinetic hormone which regulates the use of lipids as a source of energy in flight (Stone etal., 1976). 

In contrast, no insecticide has been developed to interfere specifically with the process associated with the steroidal insect molting hormone, 20-hydroxyecdysone. Although active ecdysteroids can be obtained from plant and animal sources (S), the main reason for the failure to develop them as insecticides has been that (a) their structures are too complex to produce economically, (b) their hydrophilic nature prohibits their penetration into insect cuticle, and (c) insects have powerful mechanisms to eliminate ecdysones between molts. One approach to solve these problems is to synthesize a simple molecule which can mimic ecdysone, but with appropriate chemical and transport properties, and acceptable metabolic stability. 

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