532 Invasive Stink Bugs and Related Species (Pentatomoidea)
The seasonal color polyphenism is irreversible in some species; in others, coloration changes gradually
and may be reversible. For example, the freshly molted adults of Nezara viridula may be either green or
yellow, depending on the genetic morph (a case of genetically controlled color polymorphism; see above
in this Section and in Chapter 7). The same green or yellow body coloration is preserved during repro-
duction (Figures 11.16 and 11.17A). However, diapausing individuals of both sexes turn from green or
yellow to reddish-brown soon after the adults emerge (Figures 7.1D, and Figures 11.16 and 11.17B–F;
Musolin and Numata 2003a) and retain this coloration until the complete termination of diapause. These
adult body color changes are controlled by day length and correlated with the physiological state (dia-
pause versus nondiapause) of the individual (Harris et al. 1984, Musolin and Numata 2003a, Musolin et
al. 2007, Musolin 2012).
The same pattern for Nezara viridula also was observed under field conditions in central Japan: repro-
ductive adults of the summer generations were green (or yellow), although adults of the late-season gen-
eration normally did not reproduce but changed body color to reddish-brown and entered winter diapause
(Figure 7.1C,D). After overwintering, the body color changed back to the initial green (yellow; Figure
11.17G –H), and the bugs began to reproduce (Figure 11.18; Musolin and Numata 2003b, Musolin et
al. 2010, Takeda et al. 2010). A similar pattern was observed in the field in the redbanded stink bug
Piezodorus guildinii (Zerbino et al. 2014, 2015).
Not so dramatic, but apparently an adaptive ontogenetic seasonal polyphenism was found in
Graphosoma lineatum. In Sweden, the majority of newly eclosed adults of this species appearing in
the late summer have no or very little red pigmentation. Instead, they exhibit a pale, light brownish
(epidermis) and black (melanized cuticula) striation. These adults leave their host plants for overwinter-
ing in the ground. When they appear again on their flowering host plants in early summer after winter
adult diapause, they show the typical red-and-black striation. Thus, the pale stripes turn red sometime
before the postdiapause reproductive period. It is stressed that the two broad functions of protective col-
oration, camouflage and warning coloration, need not be mutually exclusive. It also is apparent that the
five nymphal instars are all colored in various shades of brown and black and appear quite cryptic when
feeding on seeds in the dried umbels of host plants (Tullberg et al. 2008).
In Podisus maculiventris, the degree of melanization also changes over the seasons, and adults are
brighter in mid-summer than in spring or autumn. However, this response is mostly controlled by tem-
perature, not day length (Aldrich 1986).
Analysis of the above examples of seasonal body color changes in pentatomoids easily reveals the
dominant trend: the prevalence of brown coloration or dull texture of the integuments in overwintering
insects. This makes them less conspicuous, providing passive protection from predators (the seasonal
camouflage). Dark coloration also may give a certain adaptive advantage in thermoregulation, even
during the winter. However, exceptions also are known (e.g., the pentatomid Oebalus poecilus is darker
during the reproductive season than during overwintering; Albuquerque 1993).
The significance of seasonal body color changes is especially high in species forming large aggrega-
tions in winter and/or summer diapause sites; these color changes are common among pentatomoids.
It is important to note that day-length-controlled body color polyphenism has been found not only in
adults where, in some cases it precedes diapause or is not directly linked to diapause, but also has been
found in nymphs. In the nymphs of the pentatomid Plautia stali in Japan, six coloration forms (pheno-
types) can be distinguished with cuticle color varying from green to dark brown (Figure 11.19). The
incidence of these forms is controlled by photoperiod: under long-day conditions, incidence of brightly-
colored nymphs is higher; under short-day conditions, more intense pigmentation is evident. Diapause
in this species also is controlled by day length, but it is linked to the adult stage (Figure 11.19; Numata
and Kobayashi 1994).
Somewhat similar was found in the predatory pentatomid Arma custos (Volkovich and Saulich
1995). In this species, short-day and low-temperature conditions stimulated appearance of dark-colored
nymphs, whereas under long-day and high-temperature conditions incidence of nymphs with such col-
oration pattern was much lower and most or all nymphs were brightly colored (Figure 11.20). Similarly
to the just described case of Plautia stali, induction of adult diapause and body color determination in
nymphs in A. custos are two independently controlled processes because they are not only linked to dif-
ferent developmental stages (adults and nymphs) but also have different temperature optima. Thus, the