Precocene derivatives and aphid morphogenesis

The precocenes have notable effects on insect development, in particular they can induce specific destruction of corpora allatal cells and thus prevent the synthesis of juvenile hormones. As juvenile hormones have wide-ranging physiological roles in insects, from metamorphosis to reproduction, the effects of precocenes are also diverse. It has been suggested that high juvenile hormone titres in aphids induce the development of wingless adult forms while low titres promote the development of winged forms. The morphogenetic effects of precocene derivatives on aphids are complex. They can affect wing dimorphism in some species, both promoting wing development and inhibiting wing development, depending upon experimental strategy, and can exhibit the classical induction of precocious adult development indicating destruction of the corpus allatum. The morphogenetic effects promoted by a series of precocenes and 2,2-dimethylchromene derivatives have been investigated in the pea aphid, Acyrthosiphon pisum (Harris), and structure-activity relations determined for wing induction, wing inhibition, and precocious metamorphosis. These experiments show that compounds which promote wing development are not, or not so, effective in wing inhibition and that the compounds that inhibit wing formation are more closely aligned with those that induce precocious metamorphosis. Substitution of alkylthio for alkoxy groups at C7 alters the morphogenetic activity profile while 2,2-dimethylchroman derivatives have no morphogenetic activity.