Biology Reference
In-Depth Information
Figure 8.2 Larval diapause in Diatraea grandiosella. The spotted larva at the last instar
enters dormancy under high levels of JH which override the molting action of ECD to
induce the appearance of the dormant immaculate morph instead of the pupation.
Immaculate larva fails to initiate metamorphosis. After a period of chilling, the drop
of JH arrests diapause and larvae initiate normally the pupal life. Ts, target organs; F,
fat accumulation.
signaling similar to the way it does for normal larval-larval molts. In fact,
injections of ECD into immaculate larvae elicit only further immaculate-
to-immaculate molts failing to induce metamorphosis. Moreover, injections
of ECD into the body of neck-legated diapausing larvae (in which the
hemolymphatic diffusion of JH from the neurohemal glands producing it
is blocked) induce premature pupation of the segments posterior to the lig-
ature. Consistent with the pivotal role of JH, topical application of JH to
“spotted” (nondiapausing) larvae induces them to develop as immaculate
dormant morphs and continued exposure to exogenous JH maintains
diapause and enhances the number of “stationary” molts (
Chippendale,
1977, 1984
). Hemolymphatic levels of JH remain at high levels during dia-
pause after an immaculate molt. Only when JH levels decay does diapause
end and larva begin to undergo normal metamorphosis (
Chippendale, 1977,
1984; Chippendale & Yin, 1973; Saunders et al., 2002; Yin & Chippendale,
1973, 1974, 1975, 1976a, 1976b
)
Diapausing larval morphs or larval polyphenisms have also been reported
in other species (
Scott, 1979
and references therein). Asterocampa larvae
(Nymphalidae) diapause as third or fourth instar and, once diapause is ended,
they reach pupation in six larval instars rather than normal five. Larvae of
two nymphalids,
Chlosyne gorgone
and
Chlosyne nycteis
, diapause as dark larval
morphs, while
Euphydryas editha
(Nymphalidae) has a larval diapause morph
with thicker integument. The green larvae of
Plebejus icarioides
(Lycaenidae)
diapause as dark second larval instar, but they resume the green morph color
after diapause.
