Catecholamines and β-alanine in the red flour beetle, Tribolium castaneum: Roles in cuticle sclerotization and melanization

Abstract

Catecholamines and β-alanine titres were measured in a rust-red wild strain of the red flour beetle, Tribolium castaneum Herbst and in a mutant strain which has a black cuticle. During the first three days after adult eclosion, β-alanine and N-β- alanyldopamine (NBAD) are present in the former strain, but they are absent or very low in the latter. Dopamine is approx. 3-fold higher in the black than in the rust-red strain while N- acetyldopamine , the major catecholamine in both strains, is about two times more abundant in the black. Fully sclerotized rust-red elytra contain nearly ten times more NBAD than black elytra, while the latter have about ten times more dopamine. Injection of β-alanine into newly eclosed mutant adults rescues the rust-red phenotype. One-day and two-week-old adults of the black strain exhibit 2 to 3-fold higher levels of catechol oxidase activity than wild-type adults. Cuticle pigmentation is probably determined by the relative concentrations of catecholamines, β-alanine and catechol oxidase which are utilized for production of sclerotin and melanin. High dopamine titres appear to cause the black pigmentation through melanin synthesis while β-alanine and its dopamine conjugate NBAD are associated with the rust-red colouration.