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as autumnal or intermediate morphs instead of the presumptive summer
ones, and the effects depend on the timing of the injections (
Yamanaka
et al., 2000
). Thus, DH also seems to control seasonal polyphenism of
Bombyx, presumably by signaling to imaginal discs early during pupal devel-
opment (
Fig. 8.1
), in addition to its role on diapause.
Like Bombyx, the tussock moth
Orgyia thyellina
(Lymantriidae) diapauses
as an early embryo under the control of DH. This species also exhibits a
“multistage” polyphenism that is linked to dormancy (
Fig. 8.5
A). Larvae
grown during the long days of summer emerge as winged
Macropterus
mor-
phs, while autumn reared larvae develop into wingless
Brachypterus
. More-
over, pupae are also diphenic: pale pupae develop into
Macropteres
, while
dark ones become
Brachypteres
.
Macropteres
lay direct developing eggs,
Figure 8.5 Seasonal morphs and diapause in Orgyia thyellina. (A) Developing pupa
develops into Macropterus morph, which lays developing embryos because of low levels
of diapause hormone (DH). In contrast, Brachypterus moths emerge from dark pupae that
exhibit intense DH pulses. Brachypterus moths lay diapausing embryos, which exhibit
enhanced cryoprotecting potential. Dormant embryos are darker, heavier, and thicker
than developing ones. T, target organs. (B) Effects of the misregulation of DH on embry-
onic diapause. Eggs laid just after oviposition (day 0, A-D), 8 days since laying (E-H), and
embryos (I-L). Macropterus moths lay developing embryos, when reared under long days
(LD) during larval life (A, E, I). Brachypterus moths reared under short days (SD) lay diapaus-
ing embryos (B, F, J). Injection of DH into Macropterus moth induces the production of
diapausing embryos (C, G, K), instead of the developing ones. In contrast, injections of
anti-DH induce Brachypterus moths to lay developing eggs (D, H, L). The white arrow
and arrowhead indicate diapause and nondiapause eggs, respectively. The black arrows
and arrowheads indicate telson and cephalic lobes, respectively. Scale bar
¼
5mm.
Reproduced from
Uehara et al. (2011)
with the permission of PLoS One.
