Diapause in Pentatomoidea 523
The rate of spontaneous winter diapause termination in Nezara viridula depended on the photope-
riodic conditions during the preceding diapause induction and the subsequent regime. In other words,
the diapause that was induced and maintained under different photoperiodic conditions varied in its
intensity: a shorter photophase corresponded to a stronger diapause and a later onset of the postdiapause
oviposition (Figure 11.13A–D).
11.5.2 Cold Termination of Winter Diapause
Cold termination of diapause has been shown experimentally to be of primary significance for most
insect species in the Temperate Zone although under field conditions, its effect often is difficult to sepa-
rate from the spontaneous diapause termination processes (Hodek 1983, 1996, 2002).
Insect activity usually resumes after exposure of diapausing individuals to temperatures ranging
from 0 to 10°C; some species have narrower ranges of temperature favorable for diapause termination.
Negative temperatures usually hinder the diapause termination process, as do temperatures exceeding
15°C. The temperature requirements of diapausing stages are determined mostly by the living conditions
and geographic origin of the species but are almost independent of the stage at which overwintering
occurs (Saulich and Volkovich 2004).
Environmental conditions during overwintering and the diapause termination subphase (see Figure
11.1) affect the physiological state of the subsequent stages. For example, diapause in female Podisus
maculiventris was most efficiently terminated by temperature from 6 to 8°C; such conditions generally
facilitated the highest survival rate of the adults during diapause and highest reproductive indices after
diapause (e.g., fecundity). Even slight deviations from the optimal conditions during diapause may have
considerable negative consequences after diapause (e.g., low fecundity and/or survival rate; Goryshin
et al. 1989).
The duration of cold exposure required for winter diapause termination varies from 1 to 6 months
depending on the species. The neuroendocrine centers gradually resume activity in response to cold
exposure and become capable of providing immediate stimulation when the temperature rises in spring
(Tauber et al. 1986).
11.5.3 Photoperiodic Termination of Winter Diapause
After photoperiodic induction of diapause, many diapausing insect species remain sensitive to day length
and diapause in such species can be terminated by changes of photoperiodic conditions. For example, if
diapause was induced by short-day conditions, it can later be terminated by exposure to long-day con-
ditions. This type of winter diapause termination is typical of species with larval (nymphal) and adult
diapause.
Photoperiodic termination of winter diapause also is based on the interaction of spontaneous (i.e.,
horotelic) and induced (i.e., tachytelic) processes. This is indicated by the variable duration of the period
required for long-day diapause termination at different stages of diapause. During the initiation sub-
phase (see Figure 11.1), diapause is not intense/deep and not completely formed, but, nonetheless, the
diapause termination capacity is blocked most strongly. Therefore, insects transferred in autumn from
short-day to laboratory long-day conditions usually do not undergo fast photoperiodic termination of
diapause (as evidenced, for example, by oviposition in adult diapause). Later, due to the progress of the
horotelic process of diapause development, the blocking of morphogenesis becomes weaker, and the time
required for photoperiodic termination of diapause (i.e., induced, tachytelic process) gradually shortens
(Hodek 1983, 2002; Koštál 2006).
The photoperiodic responses of diapause termination sometimes show amazing similarity with those
of diapause induction, and the critical photoperiod values may be nearly the same. The coinciding PhPR
curves of diapause induction and termination may indicate that the terminating effect results from the
same physiological mechanism that controls the onset of diapause. In other cases, for example in Nezara
viridula, the PhPR curves may differ somewhat in shape, suggesting that more complicated mechanisms
are involved (Musolin et al. 2007).