Seasonal Cycles of Pentatomoidea 587
fifth instar when the day is still long (exceeding 14 hours 30 minutes) and, thus, they do not enter winter
nymphal diapause but develop directly and quickly molt to the adult stage. These adults of the first sum-
mer generation also develop directly and start oviposition without entering any dormancy because the
day is already too short for induction of the summer adult diapause at this time (<14 hours 30 minutes).
Their progeny (i.e., eggs and newly emerged nymphs) belong to the partial second generation. In response
to short day, nymphs of this generation enter diapause when they reach the fifth instar and overwinter.
In contrast to the earlier nymphs of the first summer generation, the later nymphs of the same genera-
tion reach the fifth instar after mid-August. Under already short-day conditions (<14 hours 30 minutes)
these nymphs enter facultative winter nymphal diapause and overwinter together with the fifth instars of
the partial second generation (Figure 12.17).
Thus, in Poecilocoris lewisi, the facultative summer adult diapause removes critical pressure of the
trophic factor by postponing the beginning of reproduction until the period when food is available for
the progeny. At the same time, this summer diapause does not prevent realization of the partial second
generation (Figure 12.17; Tanaka et al. 2002).
12.4 The Semivoltine (Perennial) Seasonal Cycle
Perennial seasonal cycles are widespread in the Insecta and have been found in representatives of many
orders. They are formed for different reasons and result from different modifications of univoltine sea-
sonal cycles. Transition to this strategy can be realized in various ways, for example: (1) retardation of
preadult development, (2) inclusion of a long diapause in the life cycle, and (3) extension of the adult life
span with several periods of reproduction (Danks 1992, Saulich 2010). There must be other, still unde-
scribed, models of transition to the semivoltine cycle.
So far, semivoltine seasonal cycles have not been found in pentatomoids although, potentially, they
may exist. As mentioned above, many species, in particular the pentatomids Dolycoris baccarum,
Eurydema rugosum, and Graphosoma lineatum, are known to preserve or restore photoperiodic sensi-
tivity after the first overwintering. Because of this ability, they can, potentially, form diapause more than
once during the individual life cycle and probably switch to the semivoltine seasonal cycle. Therefore, it
is quite possible that, eventually, such a strategy will be discovered in some representatives of the large
and ecologically diverse superfamily Pentatomoidea.
12.5 The Significance of Photoperiodic and Thermal Responses
for Expansion of Insects Beyond Their Natural Distribution RangesThe results of many experiments indicate that exact correspondence between seasonal development and
local conditions creates a serious obstacle to the free movement of insects even within the species’ range
(Danilevsky and Kuznetsova 1968, Saulich 1999, Volkovich 2007). However, for various reasons (e.g.,
as the result of accidental introduction, intended introduction of biological control agents, and climate
changes), insects often enter into new habitats and must adapt or perish (Musolin 2007, Musolin and
Saulich 2012b). Detailed analysis of specific examples allows one to determine the cause of success or
failure of invasion or introduction and, in some cases, to predict the possibility of naturalization of cer-
tain species outside their original ranges.
12.5.1 Natural or Accidental Invasions—Case Studies of the Southern Green Stink
Bug, Nezara viridula, and Brown Marmorated Stink Bug, Halyomorpha halys
A convenient model species for such analysis is the southern green stink bug, Nezara viridula. This
pentatomid is characterized by diffuse range expansion. It must have originated in the Ethiopian region
of Africa and dispersed first into Asia and relatively recently into Europe and the American superconti-
nent (Kavar et al. 2006). In the middle of the 19th century, N. viridula appeared on the southern islands