PHOTOPERIODIC CONTROL OF SEASONAL DEVELOPMENT
IN THE SCUTELLERID BUG, POECILOCORIS LEWISI.
S. I. Tanaka1, Y. Natuhara2, C. Imai2 & H. Numata1.
1Dept. of Bio- and Geosciences, Grad. Sch.
of Sci., Osaka City Univ., Osaka 558-8585,
Japan, E-mail: shinchan@sci.osaka-cu.ac.jp;
2Osaka City Inst. of Publ. Health and Environ.
Sci., Osaka 543-0026, Japan.
In Heteroptera, only a small number of species
overwinter at the nymphal stages, and their
seasonal adaptations remain poorly understood.
A scutellerid bug, Poecilocoris lewisi is distributed in central Japan, China and
Taiwan, and overwinters in the final (5th)
instar. In Osaka (34.5N), final instar
nymphs appear in mid-summer and then most
of them overwinter. However, a small portion
of insects emerge as adults in the same summer.
Under long-day laboratory conditions at 25C,
adults emerged without any developmental
retardation, whereas under short-day conditions
final instar nymphs entered diapause. The
critical daylength for the induction of nymphal
diapause was about 14.5h, which corresponds
to the daylength including twilight in mid-August
in Osaka. On the other hand, under long-day
conditions, female adults entered reproductive
diapause. Under quasi-natural conditions,
female adults emerging from mid-May to mid-June
started oviposition only after summer solstice.
When nymphs were collected from the field
in May and then reared under a long-day photoperiod
(LD 16:8) at 25C, female adults did not
lay eggs until 37 days after emergence. However,
females transferred to LD 13:11 on the day
of adult emergence started oviposition 20
days after the transfer. Furthermore, when
insects were reared under LD 16:8 from eggs
and transferred to LD 13:11 on the day of
adult emergence, they started oviposition
11 days after emergence. The critical daylength
for the induction of adult diapause was between
14 and 15h. This photoperiodic response results
in a shorter preoviposition period in adults
emerging from non-diapause nymphs in mid-August
than in adults after overwintering as nymphs.
Seeds of the dogwood Cornus controversa, the principal food of this species, ripen
in July in Osaka. It is suggested that adult
diapause of P. lewisi prevents reproduction until the season when
ripen seeds of host plant are available.
Index terms: Heteroptera, nymphal diapause,
adult diapause, photoperiod, host plant.
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