Nezara viridula ( L .) 379
in diapause (and then in postdiapause quiescence) and have russet coloration from late autumn to
early spring (Figure 7.11; Musolin and Numata 2003b, Musolin et al. 2010; also see Chapters 11
and 12 ). However, the value of coloration is not so apparent during the comparatively short transition
periods of diapause induction in early autumn or diapause termination in spring, or when diapause
is induced under inappropriate conditions (Musolin and Numata 2003a,b, 2004; Musolin et al. 2007,
2010; Takeda et al. 2010).
Photoperiodic conditions have a strong effect on the timing of diapause termination in Nezara
viridula, even when all the photoperiods tested are short enough to induce diapause in many (L:D
13:11) or all females (L:D 10:14 and 12:12) (Musolin and Numata 2003a). The shorter the photophase,
the longer adults remain russet and the later they start reproduction, thus the longer the duration of
diapause. Under short-day and near-critical conditions, the preoviposition period is 10–15 times lon-
ger than under long-day conditions (L:D 14:10) at the same temperature (Figure 7.12; Musolin and
Numata 2003a).
Comparison of the diapause induction response curve (i.e., diapause incidence recorded 60 days after
adult emergence) with diapause incidence recorded on days 180, 210, and 240 after adult emergence,
shows that the short-day and near-critical photoperiods differ in the effect on maintaining diapause:
the shorter the photoperiod, the longer the diapause is maintained (Figure 7.7). It remains to be shown,
however, whether the duration of diapause in Nezara viridula is determined during the diapause induc-
tion phase as a result of day-lengths experienced (Danks 1987, p. 136; Nakamura and Numata 2000), or if
the critical photoperiod for termination of diapause decreases during the further progression of diapause
development (= physiogenesis; Numata and Hidaka 1984; Danks 1987, p. 154). It is also possible that both
of these processes are involved.
7.4.4.7 Diapause Termination in the Field
In the spring, the percentage of dark-colored Nezara viridula adults in the population gradually decreases.
By mid-May in Kyoto (Takeda et al. 2010) or late May in Osaka (Figure 7.11; Musolin and Numata
2003b), all adults revert to the green coloration. At the same time, the behavior of adults changes dramat-
ically: they start to walk, bask, probe, and consume food and water (Takeda et al. 2010). In Kyoto, under
the quasi-natural conditions in 2008, the first copulation was recorded on 22 April and 50% of females
and males were active by 28 April and 2 May, respectively (Takeda et al. 2010; see Figure 11.12). By
mid-May, all adults were active. The state of reproductive organs also dramatically changes in the spring.
In 2008, ovaries of females started to show clear signs of reproductive maturation on 28 April; the sper-
matheca index (used as a measure of mating status) also increased in the late April (Takeda et al. 2010).
In males, the size and state of the ectodermal sacs changed considerably. Additionally, the size of the fat
bodies decreased further in both sexes by this time. The incidence of diapause decreased sharply from
100% in early April to 0% by mid-May and did not differ between males and females (Takeda et al.
2010). A field survey suggested that color change in spring precedes the exit from hibernacula (Kiritani
and Hokyo 1970).
7.4.4.8 Geographic Differences in Diapause Pattern
Nezara viridula is believed to be of southern origin, but occurs throughout tropical, subtropical, and
warm temperate regions (see Section 7. 3). In the areas where winters are mild, and long-term cold
does not occur regularly, it may be advantageous for an insect population to be able to terminate winter
diapause within a few months without having a requirement for low temperature exposure. Even though
the overwintering physiology in the more southern populations of N. viridula has not been studied in
detail, it is known that diapause in this species lasts only about two months in Australia (29°S; Coombs
2004). Nearer to the equator, populations of N. viridula may have no diapause as such, and low levels of
reproduction are observed during the colder weeks or months in India (23°N; Singh 1973) and southern
Brazil (23°S; Panizzi and Hirose 1995; Antônio R. Panizzi, personal communication). The expansion
of N. viridula into both northern and southern temperate zones probably has been associated with the
evolution of a more intensive and stable diapause, which seems to be necessary for survival in more