Abstract
The concentrations of free amino acids, which were determined from haemolymph of individual fourth and fifth instars of Triatoma infestans, reflect the process of moulting, but high individual variations occur, especially of the concentrations of major cuticular amino acids. Concentrations of tyrosine, valine, phenylalanine, lysine and glycine were significantly lower in fifth than in fourth instars; those of glutamate, taurine, serine and histidine significantly higher. Similar moulting-induced alterations were found in bugs infected with the flagellate Blastocrithidia triatomae which causes reduced tanning in T. infestans. In infected fourth instars concentrations of methionine, tyrosine, alanine, arginine and histidine were significantly lower than in uninfected fourth instars. In fifth instars the infection also caused a lower concentration of these amino acids, but additionally an increase of concentrations of cyst(e)ine, lysine, aspartate and valine. Only in infected fifth instars was free β-alanine found in the haemolymph. This indicates that the reduced tanning might be caused by a low concentration of tyrosine and its metabolite dihydroxy-phenylalanine, thereby allowing no further conversion of β-alanine to β-alanyl-dopamine.
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