596 Invasive Stink Bugs and Related Species (Pentatomoidea)
seasonal development of individual species and populations. Still, the available original and published
data allow us to discuss the reasons and regularities of formation of the various seasonal patterns within
Pentatomidae and some other related families of true bugs and the eco-physiological responses involved
in their formation.
Among the 82 pentatomoid species analyzed (see Chapter 11, Table 11.2, for the list), the great
majority of species is characterized by the potentially multivoltine seasonal cycle with a facultative
winter adult diapause regulated by the PhPR of diapause induction of the long-day type. This property is
realized in the polyphagous species occurring in the regions with moderate humidity and temperatures
at middle and low latitudes, given the optimal trophic conditions and the choice of host plants (for phy-
tophages) or prey (for predators). The number of realized annual generations largely depends on local
thermal conditions, whereas day length acts as a cue and provides information necessary for optimal
timing of active development and dormancy in the given location.
However, under actual natural conditions in the Temperate Zone, few species of pentatomoids produce
more than one annual generation. The number of realized generations often is reduced in much of the
species’ range. Thus, for example, populations living at high and middle latitudes are usually univoltine.
The main factors limiting the number of generations are food and temperature. Transition to univoltine
development often is observed in the climatic belts where thermal conditions exceed the requirements of
one generation but are not sufficient for completion of two generations within one vegetation season. To
stop the series of nondiapausing generations at the only stage capable of overwintering, the population
requires a reliable cue to warn it of the impending changes in the environment. The day length usually
acts as such a cue for cessation of active development and transition to seasonal dormancy. The exact
eco-physiological mechanisms involved in each particular case can be determined only in special experi-
ments: they may include an increase in the thermal optimum of the PhPR of diapause induction (as in
Arma custos), a high critical photoperiod (as in pentatomids of the genus Graphosoma), and likely other
responses ensuring the timely formation of diapause.
The univoltine seasonal cycle based on obligate diapause is quite rare in Pentatomoidea but still has
been found in species with different types of winter diapause: embryonic (e.g., in Apoecilus cynicus,
A. bracteatus, and Picromerus bidens), nymphal (e.g., in Pentatoma rufipes), and adult (e.g., in Palomena
prasina and P. angulosa). The onset of diapause usually corresponds strictly to the period to which dia-
pause is adapted; otherwise, overwintering would be unsuccessful. Precise seasonal timing of diapause
induction can be ensured in different ways. Species with embryonic and nymphal diapause have acquired
adaptations slowing down the preadult development, so that the only stage capable of overwintering can
be shifted onto the autumn period. This is accomplished by inclusion of facultative adult estivation into
the seasonal cycle (e.g., in P. bidens), the result of which shifts oviposition to a later period, more favor-
able for the overwintering eggs. In species with winter adult diapause (e.g., in the genus Palomena), the
nymphal growth rate is controlled by day length: decelerated under long-day conditions and accelerated
under short-day conditions. This seasonal adaptation solves the opposite problem, allowing the only
overwintering stage (the adult) to appear before the autumn drop of temperature when preparation to
diapause would be difficult. The above seasonal adaptations have the same effect: the diapausing stage
is formed during a specific period of the year. In both cases, the formation of obligate winter diapause is
determined hereditarily in each generation, but the exact timing of appearance of the diapausing stage is
completely controlled by day length.
Adaptation of invasive species to new conditions is difficult, regardless of the type of seasonal cycle.
Polyphagous species with a univoltine seasonal cycle based on obligate diapause, which is to some extent
independent of the environmental conditions, adapt more easily. The species or populations with a mul-
tivoltine cycle, whose seasonal development is controlled by external conditions and strictly depends on
the local climate, face the greatest difficulties when relocated. One of the main obstacles to naturaliza-
tion is a mismatch between the parameters of the PhPR of diapause induction of the introduced popula-
tion and the new climatic conditions. If this obstacle is overcome, the phases of the life cycle become
synchronized with the periods of the year to which they are adapted.
The same seasonal adaptations participate in formation of different types of seasonal cycle, but their
occurrence can vary between taxa. In particular, photoperiodic regulation of the growth rate is used both
in univoltine (obligate or exogenously controlled) and in multivoltine cycles, but this adaptation seems to