Nezara viridula ( L .) 375
evidence that adult body color change is controlled by day length, not only qualitatively (russet versus
green coloration), but also quantitatively (different rates of color change under different photoperiodic
conditions).
The color change in adult Nezara viridula is associated strongly with gonadal development. Two
months after adult emergence, under the short-day conditions (L:D 10:14) at 20 and 25°C, the gonads
of all individuals are in a diapause state, and the adults are deeply russet brown; conversely, almost all
adults are reproductively active and green under the long-day conditions at the same temperatures (com-
pare Figures 7.8 and 7.9). Under the near-critical conditions of photoperiods L:D 12:12 and L:D 13:11,
all color grades (i.e., green, intermediate, and russet) and both diapausing and nondiapausing adults were
present (Figure 7.10). It is important to note that under such near-critical photoperiodic conditions, on
the day of dissection, diapausing individuals can have different body colors (i.e., green, intermediate, and
russet). The same is true for nondiapausing adults – they can have different body colors. However, even
though most of the green adults are reproductive (i.e., nondiapausing) under such conditions, some of
them are considered to be in diapause (judged by the state of their reproductive organs). The same is true
for intermediately colored or russet adults – some of them might be in diapause whereas others under the
same conditions might be in nondiapause (Figure 7.10). These results show that winter diapause induc-
tion and adult body color change are complex and dynamic processes (Musolin and Numata 2003a; also
see Chapter 11).
The strong link between winter diapause and body coloration in Nezara viridula adults suggested that
body color could serve as a reliable indicator of diapause in this species (Harris et al. 1984); however, the
reliability of coloration as an indicator of diapause is contradicted (Seymour and Bowman 1994), and the
issue is discussed in detail below.
7.4.4.3 Diapause Induction and Adult Color Change in the Field
In central Japan, the nonreproductive adults of the final annual generation of Nezara viridula typically
start to change body color from green/yellow to intermediate/russet in mid-October. The percentage of
russet adults in the population reaches a plateau of 85–100% between late November and mid-January
and continues to April (Figures 7.11 and 7.14; Musolin and Numata 2003b, Musolin et al. 2010, Takeda
et al. 2010). Beginning in October, adults minimize their walking and probing activities, as well as their
consumption of food and water. They aggregate under large leaves or other shelters (Figure 7.1D and
Figure 11.17). Their reproductive organs are in a diapause state (Figures 11.11 and 11.12). In females,
the ovaries are clear and contain no oocytes in the germaria. The spermathecae are also small and empty.
In males, the ectodermal sacs are transparent, empty, collapsed, and not readily visible. Diapausing
adults of both sexes accumulate fat reserves and their fat bodies are extended and dense (Esquivel 2009,
2011; Takeda et al. 2010).
Field experiments have clarified the importance of the two leading environmental factors (namely,
day length [= photoperiod] and temperature) in preparation for overwintering in Nezara viridula. Even
though the shortening autumn days accelerate color change in the last annual (= overwintering) genera-
tion of the species, relatively high temperatures are necessary for the successful preparation for diapause
120
80
40
0
Green
Intermediate
Russet
NondiapauseDiapause100
802040600
Green
Intermediate
Russet
NondiapauseDiapauseL:D 12:12 L:D 13:11Number of insectsFIGURE 7.10 Diapause status and color of adult Nezara viridula at day 60 after emergence at L:D 12:12 and L:D 13:11
and 25°C (the sexes are combined). (From D. L. Musolin and H. Numata, Physiological Entomology 28: 65–74, 2003a,
with permission.)