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Résumé :
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The relationship between the structure of nineteen 2,2-dimethylchromene derivatives and their effects on aphid morphogenesis were investigated in a pink clone of the pea aphid, Acyrthosiphon pisum (Harris). Three bioassay systems were used: (1) wing induction-the induction of winged (alate) progeny by winged adults that normally produce only wingless (apterous) daughters, (2) wing inhibition-the inhibition of production of winged progeny by wingless adults that had been crowd-induced to promote the appearance of winged progeny, (3) the effect on metamorphosis-the production of precocious adults indicating a decrease in juvenile hormone titre or the induction of supernumerary moults indicating a juvenile hormone agonist effect. Compounds demonstrating wing-promoting effects had short (less than or equal to 2 carbon) side chains at the C6 and/or C7 positions while methylation of C5 tended to decrease this activity. Of the seven compounds inducing wing formation, three also inhibited the production of winged progeny. However, the compounds affecting metamorphosis, in particular promoting precocious adult development, were similar to those that promoted wing inhibition rather than those with wing inducing effects; they had alkoxy groups at C7 with lengths of greater than or equal to 2 carbons. There is a stronger correlation between compounds interfering with metamorphosis (and therefore evidenced to be affecting juvenile hormone levels, a classic property of some 2,2-dimethylchromene derivatives) and the promotion of wingless forms than the induction of winged forms. This finding is in contradiction to the idea that juvenile hormones are involved in promoting wingless forms. In addition, attempts to reduce the wing-inducing properties of Precocene II (the most potent compound effecting wing induction) by subsequent treatment with juvenile hormone III or the juvenile hormone analogue, pyriproxyfen, were inconclusive and attempts to inhibit wing formation with these two compounds after crowding were also unsuccessful. The precise mode of action of the 2,2-dimethylchromenes in relation to aphid wing induction remains unclear but it seems likely that the effect is not related to changes in juvenile hormone titres. (C) 1995 Wiley-Liss, Inc.
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