592 Invasive Stink Bugs and Related Species (Pentatomoidea)
that older nymphs and adults are more sensitive to day length than younger nymphs (Niva 2003, Niva
and Takeda 2003).
In the bivoltine seasonal cycle exhibited in southern China, adults of the first generation of Halyomorpha
halys emerge in late June or early July when local photoperiodic conditions do not limit the possibility
of a second generation because day length during adult emergence is longer than the critical photoperiod
(Lee et al. 2013). As a result, adults of this generation are reproductive. In contrast, adults of the second
generation emerge in late August or early September and enter facultative winter adult diapause because
the natural day length at that time is already short.
The seasonal cycle of Halyomorpha halys also is well studied within its invasive range. In Pennsylvania
and New Jersey, the United States of America, only one generation per year is recorded. In these regions,
the SET for a full generation is approximately 700 degree-days with the LDT of 14°C. The peak of abun-
dance of the bug was recorded in August, when the accumulated SET is approximately 800–1,000 degree-
days, thus determining univoltine seasonal development in this part of the invasive range (Nielsen and
Hamilton 2009, Leskey et al. 2012). At this time of year, natural day length becomes short, strongly limit-
ing further active development of the species and promoting induction of facultative winter adult diapause.
In another part of the invasive range – in Switzerland, Europe – Halyomorpha halys is strictly uni-
voltine (Haye et al. 2014). Adults of the summer generation emerge in mid-August when natural day
length can be as short as 14 hours 15 minutes. The critical photoperiod of the PhPR of diapause induction
of the local population is not known but it likely is close to the one estimated for the Nagano population
(15 hours). Short-day conditions apparently prevent reproduction of these adults and promote induction
of the winter adult diapause. To ensure successful realization of two complete generations, adults of the
first generation should emerge no later than in late June when the day is longer than 15 hours; this does
not happen under natural conditions.
The available body of information on distribution and seasonal development of Halyomorpha halys in
its invasive range does not allow one to confidently predict the further secondary range of this dangerous
invader. Zhu et al. (2012) suggested that H. halys potentially could become established in nearly all parts
of Europe, but southern Europe would be the most favorable. Recently, it has been found in northern Italy
(Haye et al. 2014) and Greece (Milonas and Partsinevelos 2014). It is likely that the species will continue
to spread at least throughout the Mediterranean area. Temperature conditions in southern Europe would
clearly be more favorable for its development, which can result in production of two or even more annual
generations in many regions.
12.5.2 Intentional Introductions—Case Studies of the Spined Soldier Bug,
Podisus maculiventris, and Twospotted Stink Bug, Perillus bioculatus
Two North American predatory pentatomids, Podisus maculiventris and Perillus bioculatus (F.), can
serve as examples of intentional introductions of true bugs into several European countries that were
imported with the sole purpose of controlling two invasive and economically important pests, the fall
webworm, Hyphantria cunea (Lepidoptera: Arctiidae), and the Colorado potato beetle, Leptinotarsa
decemlineata Say (Coleoptera: Chrysomelidae), respectively. Both phytophagous pests have natural
ranges more or less similar to those of the two predatory bugs, and both pests became successfully
established in Europe in the 20th century. Based on the similarity of these ranges, it was expected that
the predatory bugs also would become successfully established on a new continent. However, fates of
these two introduced pentatomids in Europe differ substantially. Extensive research programs resulted
in a large body of eco-physiological information, which improved our understanding of the possibilities
of introductions and naturalization of pest and useful insects.
Availability of suitable food, a SET sufficient for at least one annual generation, and ability to survive
cold season (usually in a state of diapause) are the main conditions that determine the possibility and
success of any invasion or introduction to a new region. If at least these three conditions are met, then the
initial invasion/introduction and survival are possible. For further naturalization, the seasonal cycle of
the species should become well adapted to and coordinated with local environmental conditions.
As discussed in Chapter 11, day length plays a dual signal function: (1) it acts as a trigger controlling
seasonal changes of eco-physiological states of an organism (e.g., induction or termination of diapause