Seasonal Cycles of Pentatomoidea 573
12.2.1.3 The Univoltine Seasonal Cycle Based on Obligate Adult Diapause
Strictly univoltine seasonal cycle with obligate adult diapause over the entire range of a species is well
documented in the sunn pest, Eurygaster integriceps Puton, a serious agricultural pest. The activity of
this species is limited to only 2.5–3.0 months per year. During the remaining 9.0–9.5 months, the bugs
are in dormancy, which is formed in young adults in June–July and lasts until the next spring. This pro-
longed dormancy of adults consists of two stages – summer diapause (i.e., estivation) and winter diapause
(i.e., hibernation). The first stage starts after a short but intensive prediapause feeding, which is followed
by migration of adults into their estivation quarters. In the lowland regions, forest edges, meadows, arti-
ficial tree belts, parks, and gardens can be used as estivation quarters. In mountainous regions, the bugs
can fly up to 2,500–2,800 meters a.s.l. Summer diapause lasts about two months and during this time,
adults lose about 20% of the reserves accumulated during prediapause preparation feeding (Ushatinskaya
1955). In autumn, as summer heat decreases, adults migrate downward and overwinter in a state of obli-
gate winter adult diapause. Survival over a long period with such contrasting conditions is possible only
because of the reserves accumulated during the prediapause feeding. In addition to the usual accumula-
tion of fat in the fat body, E. integriceps, and related species, can accumulate half-digested food (such as
starch) in the first section of the midgut (Fedotov 1947). These accumulated reserves provide resources
not only for survival during the whole dormancy period but also for maturation of sperm during winter
and the next spring (Shinyaeva 1980), a phenomenon very unusual for Heteroptera.
Maturation of males before winter, and difference in diapause development between sexes, may not
be as rare as was believed in the past. The pentatomid Menida disjecta (= M. scotti), found in Asia, has
a univoltine seasonal cycle in Japan with an obligate winter adult diapause. The physiological states of
females and males, however, differ during the winter. Even though adult diapause is obligate, males
already have mature sperm in autumn and copulate with females during the winter. While mating, the
males transfer nutrients to females, which likely increase the females’ chances of successfully overwin-
tering. Egg maturation in females, however, starts only in spring (Koshiyama et al. 1993, 1994).
A population of the green shield bug, Palomena prasina, from the forest-steppe zone of Russia
(Belgorod Province, 50°N), has been studied experimentally. In spring, after a short period of feeding,
overwintered adults start ovipositing, which lasts until the end of July. The nymphs feed, grow slowly,
and begin to molt to adults by mid- to late July. These adults hibernate after a period of prediapause feed-
ing (Figure 12.5; Saulich and Musolin 1996).
In the laboratory, Palomena prasina invariably formed adult diapause at all photoperiodic and tem-
perature regimes tested, and reproduction could not be induced by any special conditions. Based on
these results, we concluded that winter adult diapause in P. prasina is obligate. However, day length
still had a certain regulatory effect on seasonal development of the species, influencing the growth rate
of the nymphs (Saulich and Musolin 1996, Musolin and Saulich 1997): the shorter the day length, the
faster the nymphs grew. The difference in the growth rate became noticeable by the third instar and
increased gradually, reaching the maximum in the fifth instar. This growth acceleration was recorded
at all temperature regimes tested (20, 26, and 30°C), being the greatest at 20°C. At this temperature,
nymphs reared under short-day conditions molted to adults almost 20 days earlier than those under
OOO eggs – – – nymphs +++ adults
IV V VI VIIVIII IX XOOOOOOOOOOOO++++++++++
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–––––––––FIGURE 12.5 Seasonal development of the green shield bug Palomena prasina in the forest-steppe zone (Belgorod Province,
Russia; 50°N). Vertical line marks the date when the natural day length plus half the civil twilight equals 15 hours; months are
indicated on the top of the figure (Data from D. L. Musolin. Ph. D. Dissertation in Biology. Saint Petersburg, Russia, 1997.)