572 Invasive Stink Bugs and Related Species (Pentatomoidea)
photoperiods failed to provoke direct (i.e., nondiapause) development of nymphs: all of them formed
diapause in the third and fourth instars, and none of them molted into the fifth instar before diapause
(Musolin 1997). Nymphs completed metamorphosis only after overwintering in spring – they molted
into the fifth instar, became adults, and continued ontogenesis. Their progeny grew slowly and entered
obligate nymphal diapause as third and fourth instars.
Apparently, some nymphs reach the diapausing stage as early as mid-July or early August. Adaptive
value of such a seasonal pattern of Coptosoma scutellatum is not clear. Early formation of winter dia-
pause (in July) seems not to be efficient, as the vegetative season is not fully used for feeding and growth.
Moreover, diapausing nymphs do not actively move during dormancy and, thus, are more susceptible
in summer and autumn to abiotic and biotic influence than nondiapausing older nymphs and adults.
Nevertheless, such dormant nymphs experience and must survive the hottest period of summer (Musolin
1997, Saulich and Musolin 2014a).
It then was suggested by Musolin (1997) that in addition to the winter nymphal diapause in the fourth
instar, Coptosoma scutellatum might pass mid-summer in the state of summer diapause in the younger
(most likely the third) instar. This hypothesis was supported indirectly by observations in the field and
laboratory. Thus, under the outdoor conditions in Ukraine, first and second instars last (in total) 25–30
days and the third instar about another month (Putshkov 1961).
According to laboratory data obtained at 24.5°C, third instars took twice as long to develop under
long-day L:D 18:6 conditions (on average 22.5 days) than under short-day L:D 15:9 conditions (on aver-
age 10.6 days; Musolin 1997). It is likely that this pronounced photoperiodically controlled retardation
of nymphal growth during the third instar postpones molting into the fourth instar in which nymphs
enter winter diapause. Moreover, in the laboratory, starting from the third instars, nymphs were reluc-
tant to move from old food to new food, whereas younger nymphs did so quickly. In such cases, we
can suppose that in the seasonal cycle of Coptosoma scutellatum, there are two dormancy periods:
facultative summer diapause of third instars and obligate winter diapause of fourth instars. These two
dormancy periods might look like a single long summer–winter diapause of third and fourth instars.
Similar patterns are known in many insect species with prolonged diapause of an unclear nature that
starts early or in the middle of summer. To better understand the nature of the dormancy and structure
of the seasonal cycle of this species, additional eco-physiological research in the field and laboratory
is needed.
Coptosoma mucronatum Seedenstücker is a second East-Palaearctic plataspid species studied in the
neighboring region – southern Slovakia. Ecologically, it is similar to C. scutellatum and has a similar
seasonal cycle (Figure 12.4). Older nymphs of both plataspid species can be parasitized by the braconid
Aridelus egregius (Schmiedeknecht) (Hymenoptera: Braconidae, Euphorinae). Development of parasit-
ized nymphs is retarded, fifth instars appear somewhat later in the season than nonparasitized nymphs
(Figure 12.4), and these nymphs cannot become adults (Davidová-Vilimová and Štys 1982).
The forest bug, Pentatoma rufipes, is a typical large pentatomid that is widespread in the Palaearctic
and inhabits broad-leaved forests. Detailed phenological data confirming univoltinism of this species
have been obtained from southwestern England. The species apparently overwinters as young nymphs,
as tiny nymphs have been seen in September and large third and fourth instar nymphs have been recorded
in May. Fifth instar nymphs typically are found in June–July and adults mostly in July–September.
Copulation has been recorded in August and September (Hawkins 2003). Nymphal diapause probably is
obligate, which ensures the univoltine seasonal cycle of this pentatomid across its entire range (Putshkov
1961). Some cases of overwintering adults of P. rufipes have been recorded (Southwood and Leston
1959), but it is likely that only the adults infested with phasiinine flies (Diptera: Tachinidae) can over-
winter. The bivoltine tachinid fly Phasia hemiptera (F.) is known to parasitize P. rufipes in spring and
the green shield bug, Palomena prasina, in autumn (Sun and Marshall 2003).
Univoltine seasonal development with nymphal (and likely obligate) diapause also is recorded in
the shieldbacked bugs Odontoscelis fuliginosa ( L .), Odontoscelis dorsalis (F.), and Irochrotus lanatus
(Pallas) (Putshkov 1961).
In general, seasonal cycles with overwintering nymphs are quite rare in Pentatomoidea and other true
bugs. They have been recorded in no more than 1.7–11.0% of the species that have been studied, accord-
ing to various sources (Saulich and Musolin 2007b; also see Chapter 11, Table 11.2).