Tyrosine and catecholamine levels in the hemolymph of tobacco hornworm larvae, Manduca sexta, parasitized by the braconid wasp, Cotesia congregata, and in the developing parasitoids.

摘要

Parasitism of fifth-instar larvae of Manduca sexta by the gregarious parasitoid Cotesia congregata prevented normal storage of tyrosine in the haemolymph, whereas total tyrosine concentration increased over eight times in the haemolymph of unparasitized larvae by day 4. Tyrosine glucoside, the haemolymph storage form of tyrosine and the precursor for pupal cuticle sclerotizing agents, was found only in trace amounts in parasitized larvae at the time of parasitoid emergence, but had increased to over 6 mM in the haemolymph of unparasitized larvae. Concentrations of dopamine and N-beta-alanyldopamine (NBAD), precursors for melanization and sclerotization of cuticle, respectively, had approximately doubled in the haemolymph of parasitized larvae by the day of parasitoid emergence, but not in unparasitized larvae. Catecholamine biosynthesis may be transiently stimulated for wound-healing, as black melanic pigmentation appeared around the wasp emergence holes in the host integument. C. congregata larvae accumulated tyrosine, dopamine, and NBAD by the time of emergence and cocoon spinning, either by direct uptake or by synthesis from precursors obtained from the host. NBAD increased in parasitoid larvae close to pupation, suggesting it functions as the main precursor for pupal cuticle tanning. Both dopamine and NBAD increased dramatically in pharate adult wasps just before eclosion and N-acetyldopamine (NADA) appeared for the first time. Dopamine was highest in concentration and total amount, and itserved both as a precursor for black melanic pigmentation of adult wasp cuticle and for synthesis of NADA and NBAD, the precursors for cuticle sclerotization.