Metabolic origin of 3,4-dihydroxyphenylacetic acid in Tenebrio molitor and differences in its content in larval, pupal, and adult cuticle

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Abstract
Pupal exuviae from Tenebrio molitor differ from larval exuviae and adult cuticle in that they lack 3,4-dihydroxyphenylacetic acid (3,4-DPA), a phenolic compound thought to be characteristic of coleopteran cuticle. This difference is not due to an absence of all cuticular o-dihydricphenols since all three cuticles yield comparable amounts of ketocatechol. The significance of this previously unreported stage difference is discussed in the light of the various functions proposed for 3,4-DPA in insect cuticle. Tyrosine is shown to be the primary precursor of 3,4-DPA in adult cuticle. Dopamine and N-acetyldopamine appear to make only a minor contribution to its formation.