Diapause in Pentatomoidea 501
adult (sometimes called reproductive, or imaginal) diapause (Table 11.1). However, each species of
insects, as a rule, can form diapause only at one particular developmental stage. Often (if not always),
even within one stadium, there is a strict association of diapause with a particular ontogenetic stage.
Cobben (1968) gave 16 different species-specific examples of timing of diapause only within the embry-
onic diapause in Heteroptera.
In the literature, however, there are examples of overwintering of insects from the same species or
population at different stages of their life cycle. For example, nymphs and adults have been reported
to overwinter together in Ischnodemus sabuleti (Fallen) (Lygaeidae; Tischler 1960) and Chiloxanthus
pilosus (Fallen) (Saldidae; Cobben 1968). Finally, some species of true bugs have life cycles that last two
or even more years and, thus, these species form diapause more than once in their life cycle; it usually
happens during different developmental stadia (e.g., in Aradidae, Aphelocheiridae, and Reduviidae).
11.2.3 Two Forms of Diapause: Obligate and Facultative Diapause
As briefly mentioned above, diapause in insects may be of two forms. In some species, diapause is
obligate (or obligatory) in which case, it does not need to be induced; it is determined hereditarily and
always present in each generation regardless of external conditions. Obligate diapause in a particular
species strictly determines a univoltine seasonal cycle (i.e., a pattern with one generation per year)
over the entire range of the species because, in this case, active development is interrupted by obligate
diapause in each generation (see Chapter 12). In other cases, diapause is facultative, and, therefore, it
is induced by external (i.e., exogenous) factors and does not occur necessarily in each generation (Table
11.1). The facultative nature of diapause makes it possible to produce two or more generations during a
year, with individuals of the last generation in the season entering facultative winter diapause.
Due to the facultative nature of diapause, different geographic populations of some species can pro-
duce different numbers of annual generations. Volt i n i s m may also differ between particularly cold and
warm years even in the same location.
In Pentatomoidea, both forms of diapause (i.e., facultative and obligate) have been documented. Among
79 experimentally studied species of stink bugs and their allies that have winter diapause, 29 species (about 37%)
had an obligate winter diapause, whereas others (about 63%) had a facultative winter diapause (Table 11.1).
At the same time, no pronounced relationship between the form of diapause (i.e., facultative or obli-
gate) and its type (i.e., association with a particular developmental stage – embryonic, nymphal or adult)
TABLE 11.1
Different Forms and Types of Winter Diapause in Pentatomoidea
Family
Total Number of
Species StudiedAssociations between Two Forms (Obligate and Facultative)
and Three Types of Winter Diapause^1
Embryonic Nymphal AdultAcanthosomatidae 5 O – 3; F – 2
Cydnidae 6 O – 4; F – 2
Parastrachiidae 1 O – 1
Pentatomidae^248 O – 2; F – 1 O – 1; F – 1 O – 3; F – 38
Plataspidae 4 O – 2 F – 2
Scutelleridae^211 O – 3; F – 1 O – 4; F – 2
Tessaratomidae 2 O – 1 O – 1
Thaumastocoridae 1 F – 1
Thyreocoridae 4 O – 4
Subtotal O – 2; F – 1 O – 7; F – 2 O – 20; F – 47
Total^2823967
(^1) Forms of diapause: F – facultative, O – obligate.
(^2) In the rows Pentatomidae, Scutelleridae, and Total, the total number of species studied differs from the total number of diapause
cases because some species do not have winter diapause (they have homodynamic seasonal development; see Section 11.2.3).