Biology Reference
In-Depth Information
Figure 8.3 Model of pupal diapause in Manduca sexta. Under short days of autumn,
diapausing last fifth instar larvae exhibit normal temporal profiles of both ECD (in
red) and prothoracicotropic hormone (PTTH, in blue), but they metamorphose into dia-
pausing pupae. In diapausing pupae, PTTH falls down and the ECD pulse is not elicited
any more blocking the metamorphic progression and triggering dormancy. After an
established period of chilling, PTTH and ECD pulses are resumed and the metamorpho-
sis progresses without reporting growth defects (Ts, target organs). During the pupal
stage, diapausing animals exhibit low levels of 20-hydroxy-ecdysone (20ECD) compared
to nondiapausing ones. Red and blue arrowheads indicate diapausing and
“
nondia-
pausing
”
animals, respectively. Graph redrawn from
Saunders et al. (2002)
.
but its expression is strongly downregulated in diapausing pupae compared
to developing ones (in
Xu & Denlinger, 2004
). Similarly,
ptth
expression is
downregulated in diapausing pupae of
Heliothis virescens
(
Xu & Denlinger,
2003
) and
Helicoverpa armigera
(
Wei, Zhang, Kang, Xu, & Denlinger,
2005
). Consistent with the idea that low PTTH levels are responsible for
the induction of diapause, injections of PTTH induce the termination of
pupal dormancy in noctuids of Heliothis/Helicoverpa complex (
Wei
et al., 2005
). Similarly, injections of PTTH in both
Manduca sexta
and
Anthaerea pernyi
stimulate the resumption of metamorphic growth in both
normal diapausing pupae as well as in brain-less (brain surgically removed)
dormant ones that are arrested in permanent diapause (
Sauman & Reppert,
