Seasonal Cycles of Pentatomoidea 567
taxa studied (Danilevsky 1961, Tauber et al. 1986, Danks 1987). It usually is based on the photoperi-
odic response (PhPR) of facultative diapause induction of the long-day type; diapause is induced by
a decrease in day length in autumn often combined with a decrease in temperature (Chapter 11). The
system synchronizing the multivoltine seasonal development of insects with the periodically chang-
ing external conditions is made more reliable by the ability of different species to respond simultane-
ously to different external factors such as temperature (both its mean value and the daily and seasonal
rhythms), seasonal dynamics of day length, and qualitative composition of diet. Therefore, due to the
modifying effects of external conditions on the parameters of the PhPR of diapause induction, the tim-
ing of diapause and the number of annual generations can vary depending on the weather conditions of
a given year. The geographic variation of PhPR of diapause induction brings the seasonal cycle of each
geographic population into strict correspondence with the specific traits of the local climatic conditions
(Chapter 11 and references cited therein).
A comparatively small proportion of insect species or populations develop slowly and fail to finish
the preadult development within one calendar year. This is more typical of polar regions with limited
thermal conditions or low temperature environments (such as caves or mountain streams). Under such
conditions, insects may have semivoltine seasonal cycles that extend over two years or even longer.
In studies of insect seasonal cycles, of greatest interest is the geographic variation of voltinism and dia-
pause. According to climatic zonality, the annual number of generations of most insects in the Northern
Hemisphere increases from north to south. Usually, there is a regular transition from semi- or univolt-
inism in the northern parts of the species’ range to bi- and multivoltinism and, finally, to the homody-
namic seasonal cycle in the south. In many cases, the parameters of diapause, such as intensity, duration,
and tendency to form diapause, are modified in tropical populations but diapause is not completely lost
(Denlinger 1986). In the Northern Hemisphere, most of the potentially multivoltine species of true bugs
and other insects become univoltine or even semivoltine at the northern bound aries of their distribution.
On the contrary, in the Southern Hemisphere, potentially multivoltine species switch to univoltine devel-
opment towards the Southern Pole (Danks 1987, Saulich and Musolin 1996, Saulich 2010).
However, this rule has exceptions. Thus, stable annual development of more than one generation in the
north of the species’ range rarely is observed but has been recorded. For example, Nezara viridula, in
Japan, has two or even three generations a year even close to its northern distribution boundary (Kiritani
et al. 1963; Musolin and Numata 2003a,b; Musolin 2007, 2012; Chapters 7 and 11).
In this chapter, we analyze the most studied seasonal development patterns of the Pentatomoidea
living in the temperate climate, attempt to reveal the eco-physiological mechanisms participating in
the formation of a certain type of seasonal cycle, and estimate the similarities and differences in the
seasonal development patterns of species of different taxa within this superfamily of true bugs. The avail-
able published data and our own experimental material mostly focus on 3 out of 11 presently recognized
subfamilies of Pentatomidae (Asopinae [= Stiretrinae], Pentatominae, and Podopinae) because only a
few examples are available for other pentatomoid families. Unfortunately, the great majority of true bugs
of the world have not been studied as yet in respect to their seasonal development and the control mech-
anisms of their seasonal cycles.
12.2 The Univoltine Seasonal Cycle
In the univoltine seasonal cycle, only one generation develops during a vegetative season or year. Until
recently, it had been assumed that the only cause of univoltinism was obligate diapause that formed in
each development cycle (generation) regardless of the external conditions. However, it now is known
that a univoltine seasonal cycle can be maintained in a variety of ways, but the exact eco-physiological
mechanisms underlying it can be revealed only by special experiments (Saulich and Musolin 1996,
Saulich and Volkovich 1996).
Univoltinism presently is subdivided into endogenous univoltinism (based on obligate diapause in
each generation) and exogenous univoltinism (controlled by external factors that limit the number of
generations to only one per year in different parts of the ranges of potentially multivoltine species).