Seasonal Cycles of Pentatomoidea 593
and reproduction) and (2) also is used for synchronization of seasonal development of different compo-
nents of the ecosystem (e.g., between a phytophagous insect and its host plant or between a parasitoid
and its insect host). Usually, both these functions are well coordinated. However, when organisms are
transferred to distant locations, coordination between the seasonal rhythm of the organisms and envi-
ronmental conditions could be seriously disturbed or successful establishment even prevented in the
new location. In such cases, diapause might still be formed, but it could happen too late or too early in
the season and, as a result, organisms might fail to form a proper diapause. In other words, day length
might still play a signal role inducing physiological change but fail to do it in appropriate time, i.e. to
successfully synchronize the seasonal development of the organism with its new environmental condi-
tions (Tyshchenko 1983).
Introduction of Podisus maculiventris into Europe was not particularly successful. Development of
one generation of this polyphagous predatory bug requires a SET of about 400 degree-days above the
LDT of 11°C (Saulich 1995, De Clercq 2000). The hibernating adults survive cooling down to –15°C
(Borisenko 1987). It was believed that all these traits would allow the predator to become naturalized in
the greater part of Europe where it would produce from one generation in the north to four generations in
the south, depending on the local temperature conditions. However, the parameters of the PhPR of adult
diapause induction of the population originating from Missouri, the United States of America (38°N),
could not ensure the timely formation of winter diapause in Europe and, thus, the survival of the species
in the temperate climate remains doubtful.
Indeed, photoperiodic sensitivity of Podisus maculiventris starts in the third instar (see Chapter 11),
which means that for proper induction of facultative winter adult diapause, the nymphs starting from
the third instar should experience day length below the critical value (13 hours 30 min). Development
of fourth and fifth instars takes 14 to 16 days at 20°C. In addition, according to experimental data, the
prediapause feeding period of adults lasts 17 to 19 more days until complete formation of diapause. Thus,
this species needs at least a month of favorable temperatures (not lower than 15 to 16°C) from the date of
the critical photoperiod until the onset of diapause (Volkovich et al. 1991b, Saulich and Musolin 2011).
The critical photoperiod for diapause induction in Podisus maculiventris (13 hours 30 min including the
civil twilights) is reached approximately on the same date (September 23 to 25) at all altitudes over Eastern
Europe. Due to this fact, the zone of possible acclimation of this species, for example, in Russia can be
determined easily. The regions favorable for the pentatomid should have a long and warm autumn, with
the temperatures of October exceeding 15 to 16°C. In Russia, such conditions occur only in the extreme
south of Krasnodar Territory. For example, in Sochi (43.5°N), the mean daily temperature drops below
12°C on October 30, whereas the SET above 11°C for the vegetative period is about 2,000 degree-days.
Such a SET value would support development of four generations of P. maculiventris, the last of which would
experience the photo-thermal conditions inducing adult diapause. The thermal requirements of diapausing
adults also would be met in this region. Thus, P. maculiventris can acclimate successfully on the Black Sea
coast of Krasnodar Territory but not further north. More northern native populations of this species, for
example, those from southern Canada, probably would have a greater potential for naturalization in
Europe (Saulich 1995).
The critical importance of the timing and duration of the day-length-sensitive stage clearly was dem-
onstrated in the comparative analysis of seasonal development outside of the natural ranges of two spe-
cies, Podisus maculiventris (population originated from North America, 38°N) and Riptortus pedestris
Thunberg [= R. clavatus (F.)] (Heteroptera, Alydidae; population originated from Japan, 35°N). These
two species are similar in many eco-physiological traits such as a SET of one full generation and facul-
tative winter adult diapause controlled by a thermostable PhPR of diapause induction with the critical
photoperiod of approximately 13 hours. However, in terms of the sensitive stage, induction of diapause in
P. maculiventris is determined by the conditions experienced mostly by nymphs starting from the third
instar and, to a lesser degree, by adults; whereas in R. pedestris, diapause induction is more flexible and
faster, being controlled by the conditions experienced by fourth and fifth instars but mostly by adults
(Numata 1985, 1990).
Ability of these two species to enter diapause outside their natural ranges was tested in field experiments
under quasi-natural conditions in the forest-steppe zone in Russia (50°N). In accordance with the tempera-
ture conditions of the region, both species potentially can produce two generations per year with emergence