Juvenile hormones and their titer regulation in Galleria mellonella

Juvenile hormones I, II and III occur in Galleria but JH II is dominant. Its concentration reaches a peak of 3 pmol/g body wt in the penultimate instar, drops to zero in the last larval instar and, except for a small peak in prepupae (0.2 pmol/g), remains undetectable until pharate adults. After emergence the titer reaches over 5 pmol/g in both sexes. Presence of JH II is associated with JH II acid; JH III acid occurs even more often, including stages lacking JH III. Brain implantation into freshly ecdysed last instar larvae effects a similar JH peak as in the penultimate instar and causes an extra larval molt. The opposite treatment, i.e. decerebration of fresh last instar larvae, elicits a continuous rise of JH II to 10 pmol/g and an increase of otherwise rare JH I to 3 pmol/g. Sham operations of these larvae or decerebration of old larvae elevate practically only JH II titer to 1–1.5 pmol/g. Implanted brain-corpora cardiaca-corpora allata complexes maintain in various hosts 0.14–1.6 pmol/g of JH II. The significance and regulation of these fluctuations in JH titer are discussed.