Seasonal Cycles of Pentatomoidea 579
Only a few multivoltine species of pentatomoids have been studied experimentally and thoroughly
analyzed in terms of the mechanisms ensuring their seasonal cycle. Detailed experimental data obtained
in the laboratory are rarely supplemented with reliable records and comprehensive analysis of seasonal
development in the field. In the following sections, we review only those few multivoltine pentatomoid
species whose seasonal development has been analyzed based on experimental data.
12.3.1 The True Multivoltine Seasonal Cycle
As mentioned above, insects having a multivoltine seasonal cycle are characterized by the number of
annual generations changing with altitude and latitude, most often under the influence of thermal con-
ditions. Such species usually develop in one generation near the poleward boundaries of their ranges,
under the conditions of heat deficit; the number of generations increases towards the equator in accor-
dance with the growing local SET. The seasonal development and timing of winter diapause in each
geographic population are adjusted to the local conditions by the specific parameters of its PhPR of
diapause induction.
An example of precise agreement between the number of completed generations and the thermal
and day-length conditions of a particular habitat is provided by the pentatomid Piezodorus hybneri
(Gmelin), which was studied in Japan (Higuchi 1994). This species is one of the major soybean pests in
southwestern Japan where it has four annual generations. The induction of the facultative winter adult
diapause of P. hybneri is controlled by a long-day type PhPR with the critical photoperiod between 12
and 13 hours (Figure 12.9). The sensitive stages are the fifth (last) instar and adult stage.
According to the laboratory data, the lower development threshold (LDT) of this species from egg
to adult is 14.2°C, and completion of its preadult development requires a SET value of about 280 degree-
days (283 for females and 278 for males). The LDT of adult maturation is 18.4°C, and oviposition starts
upon accumulation of 70 degree-days. Thus, about 350 degree-days are needed for one complete genera-
tion of Piezodorus hybneri (Higuchi 1994).
Under field conditions in Kumamoto, southwestern Japan (32.9°N), oviposition by overwintered adults
was observed in late April and early May; the timing of the subsequent oviposition peaks was consis-
tent with accumulation of the SET needed for each subsequent generation (Figure 12.10). Thus, the
thermal resources of southwestern Japan are sufficient for completion of four generations of P. hybneri,
whereas timely induction of diapause in the last (fourth) annual generation is ensured by PhPR of dia-
pause induction.
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10 11 12 13 14 15 1623 14 26 20 24 12 14Photoperiod, hFrequency, %123FIGURE 12.9 Effect of photoperiod on maturation of females of the pentatomid Piezodorus hybneri from Kumamoto,
Japan (32.9°N). Nymphs were reared to adults and then maintained at 25°C under constant photoperiodic conditions (indi-
cated under the horizontal axis). Proportions of females: 1 – mature (i.e., reproductive, or nondiapausing); 2 – with devel-
oped oocytes in ovarioles; 3 – with undeveloped oocytes (i.e., diapausing). The number of females tested is given above the
columns. (From H. Higuchi, Applied Entomology and Zoology 29: 585–592, 1994, with permission.)