Biology Reference
In-Depth Information
dormant embryos. For example, dormant pupae of
Papilio machaon
can
supercool to a temperature of
30
C,
they can remain alive for months (
Shimada, 1980
). Also just like diapausing
embryos, diapausing pupae have to remain in the cold for several months to
acquire developmental competence. Once the cold period ends, dormant
pupae can break diapause and reactivate metamorphosis if exposed to an
optimal environment (
Denlinger et al., 2012; Saunders et al., 2002
).
Pupal diapause is specified during a “sensitive period” of larval develop-
ment. In
Araschnia levana
,
Pararge aegeria
(Nymphalidae), and
Pieris Napi
(Pieridae) the pathway decision is primarily made in the middle larval instars
and most larvae shifted from long days (nondiapause trajectory) to short days
(diapause-inducing condition) after the “sensitive stage” are irreversibly
committed to the direct development and lose diapause inducibility
(
Friberg, Haugen, Dahlerus, Gotthard, & Wiklund, 2011
; Wiklund &
Friberg, 2011). While the potential for inducing diapause of “nondiapause”
larvae is restricted during development by the hormonal programming,
diapause-fated larvae maintain a potential of developmental reversibility
(
Friberg et al., 2011
). The hornworm moth,
Manduca sexta
, triggers pupal
diapause when, as larva, it is exposed to short days. This results in a failure
of the pupal ECD pulse. Interestingly, these larvae that are exposed to short
days exhibit no differences in larval ECD levels compared to “developing”
ones. However, ECD levels drop in diapausing pupae blockingmetamorphic
progression before the pharate stage (
Fig. 8.3
)(
Bowen, Bollenbacher, &
Gilbert, 1984; Bowen et al., 1985; Smith, Bowen, Bollenbacher, &
Gilbert, 1986
). That the low pupal ECD level is causative for inducing dia-
pause is suggested by the fact that dormant pupae break diapause when
injected with an ECD agonist (RH5849) (
Sielezniew & Cymborowski,
1997
). Moreover, developing pupae of
Pieris brassicae
enter into a state of per-
manent diapause if their PGs (source of ECD) are excised (
Calvez, 1976;
Pullin&Bale, 1989
). A similar ECD-based regulatorymechanism also occurs
in many other lepidopteran species (
Agui, 1975; Bodnaryk, 1985; Highnam,
1958; Islam et al., 2005; Loeb, 1982; Mishra et al., 2008; Roxstr¨m-
Lindquist, Assefaw-Redda, Rosinska, & Faye, 2005; Williams, 1946, 1952,
1968; Zhang & Denlinger, 2012
).
Since PTTH is the major neuropeptide hormone that sets the timing of
ECD pulses (
Smith &Rybczynski, 2012
), it is not surprising that its failure of
expression appears to be pivotal in eliciting pupal diapause (
Denlinger et al.,
2012; Saunders et al., 2002; Smith & Rybczynski, 2012
). For example, in
Manduca sexta
, the
MsPTTH
gene is expressed normally during larval life,
25
C, but even after freezing at
