Seasonal Cycles of Pentatomoidea 583
The SET required for completion of the developmental cycle is 480 degree-days in Aelia sibirica and
396 degree-days in A. acuminata. According to a lower SET value (by 84 degree-days), the final molt
in the first generation of A. acuminata occurs almost a week earlier, and the great majority of adults
remains reproductive (i.e., nondiapause). Under the conditions of Kustanai Province, the SET exceeding
the LDT of A. acuminata (13°C) barely exceeds 900 degree-days; therefore, even a slight decrease in
temperature will result in a situation when only some nymphs of the second generation (mostly those
hatching from early egg clusters) have sufficient time to develop into adults and properly form diapause,
whereas the remaining individuals cannot prepare for overwintering and gradually die out in winter
(Burov 1962). Due to its greater tendency for univoltinism, A. sibirica is better adapted to the conditions
of North Kazakhstan. Because adults of this species have enough time to feed before winter diapause,
they overwinter successfully and remain permanently abundant in the study region (Burov 1962).
The population of Aelia acuminata occurring in the southwest of Slovakia also shows a considerable
tendency towards univoltinism that is based, however, not on facultative but on obligate winter adult dia-
pause. Individuals of this population are highly heterogeneous with respect to voltinism. In the greater
part of the population, diapause occurs invariably in each generation whereas in the other part, diapause
is facultative. However, in Central Europe, the species usually produces only one generation even though
the critical photoperiod of the PhPR of diapause induction in the fraction with facultative diapause was
found to be much lower than in the North Kazakhstan population: between 15 and 16 hours of light
(Honěk 1969, Hodek and Honěk 1970). The female life span in this species is relatively long, reaching
two months under laboratory condition. Hodek (1977) felt the females do not fully realize their reproduc-
tive potential within one vegetative season and probably after reproduction, they can form a repeated
diapause and survive until the next year to reproduce again.
For this possibility to be realized, insects have to preserve the ability to evaluate day length during
most of their life. It is well known that photoperiodic sensitivity after winter diapause varies between
species, even among the phytophagous species with facultative winter adult diapause (Nakamura and
Numata 1995, Saulich and Musolin 2007b; see Chapter 11, Section 11.6.1). Some species lose photope-
riodic sensitivity irreversibly whereas others, in particular Aelia acuminata, lose sensitivity in autumn or
winter but restore it in early summer after a short refractory period in spring (Hodek 1971). This ability
allows the insects to form diapause more than once during their life and to switch to the multiyear adult
stage with repeated reproduction (i.e., semivoltine cycle; see Section 12.4).
Unlike Aelia acuminata, Aelia fieberi Scott does not preserve photoperiodic sensitivity after winter
diapause but loses it irreversibly so that after overwintering, the adult bugs continue ovipositing until the
end of their lives (Nakamura and Numata 1995). In the warm climate of Japan, the period favoring the
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12Incidence of diapause,%14 16 18 20 221 224
Photoperiod, hFIGURE 12.14 Photoperiodic responses of winter adult diapause induction in females of two pentatomids from the north-
ern Kazakhstan (53°N): Aelia sibirica ( 1 ) and Aelia acuminata ( 2 ). Nymphs were reared to adults and then maintained at
25°C under constant photoperiodic conditions (indicated under the horizontal axis). (From V. N. Burov, Entomologicheskoe
Obozrenie 41: 262–273, 1962, with permission.)