| Popis: |
Brains from non-diapause-bound, diapause-bound and diapausing European corn borers contain prothoracicotropic hormone (PTTH) which stimulates the prothoracic glands of both Lymantria dispar and Ostrinia nubilalis to produce ecdysone and 3-dehydroecdysone in a dose-dependent manner. At a dose of 0.75 brain equivalents, PTTH activity is highest in non-diapause-bound and diapausing prepupae. Levels are approx. 50% as high in younger 5th instars. In diapausing prepupae, PTTH activity again falls to approx. 50% after 5–8 weeks of refrigeration. Prothoracic glands from diapausing O. nubilalis prepupae were refractory to stimulation. In vivo experiments indicate that brains from diapausing prepupae have more moult-stimulating activity than those from non-diapause-bound prepupae. However, this may be due to the presence of factors other than PTTH. Based on gel filtration HPLC, the molecular weight range of the small form of O. nubilalis PTTH is 1500–3300 Da, somewhat less than the 5000–7000 Da peptide reported for other lepidopterans. |
