Cockroache; Ecology, behavior & history - W.J. Bell

hatching by nymphs increases when other protein sources
are lacking (WJB, unpubl. obs.).
Live bearing permits females to dispense with producing
a thick, protective oothecal case, and allows them to
channel the protein that would have been required for its
manufacture into present or future offspring or into their
own maintenance. Nonetheless, the burden of “wearing”
the next generation may be metabolically expensive and
impair mobility, with consequences for predator evasion
and foraging efficiency. In B. germanica, however, Lee
(1994) found no correlation between the physical load on
the female and oxygen consumption, and in N. cinerea the
mass-specific metabolic heat flux of pregnant females at
rest was actually reduced in relation to non-pregnant females.
This suggests that the energetic demands of gestation
in these species do not translate into increased metabolic
rates (Schultze-Motel and Greven, 1998). Still, most
female cockroaches feed little, if at all, during gestation,
even when offered food ad libitum in the laboratory (e.g.,
Blattella—Cochran, 1983b; Hamilton and Schal, 1988;
Rhyparobia—Engelmann and Rau, 1965; Trichoblatta—
Reuben, 1988). The most commonly offered explanation
for fasting at this time is that the cumbersome bodies of
pregnant females may increase their vulnerability to predation.
This seems reasonable, given that, first, the mass
of the reproductive product is 30% or more of female
body weight in both B. germanica (Mullins et al., 1992;
Lee, 1994) and N. cinerea (Schultze-Motel and Greven,
1998), and second, pregnant N. cinerea are demonstrably
slower than virgin females of the same age (Meller and
Greven, 1996a). Agility also may be affected. Ross (1929),
however, opined that pregnant B. germanica“do not show
any signs of being impeded by their burden” despite the
clumsy ootheca dragging from their nether regions. Loss
of agility may not be an issue in cockroaches that rely on
crypsis or thanatosis to escape predators, but the larger
body of gravid females requires a larger crevice in species
that seek protective shelter (Koehler et al., 1994; Wille,
1920). It is unknown whether the physical burden of an
egg clutch hinders flying in those species that depend on
it for evasion. Blattella karnyi females can take to the air
while carrying an impressive ootheca of up to 40 eggs
(Roth, 1985).
In viviparous D. punctata, gravid females normally
double their body weight during gestation but nonetheless
forage; the nutrient secretion of the brood sac is derived
from the maternal diet rather than stored nutrients,
particularly in early pregnancy (Stay and Coop, 1974;
WJB, unpubl. data). This species has hard, dome-shaped
tegmina (common name “beetle cockroach”) and impressive
defensive secretions (Eisner, 1958; Roth and Stay,
1958) that may permit some bravery when under attack
by ants (Fig. 1.11A). Vertebrate predators, however, are
threats, and lizards, toads, and birds have been observed
eating them in the field (Roth and Stay, 1958; WJB, pers.
obs.). It is possible that D. punctata females rely on readily
accessible, predictable sources of high-quality food for
supporting the explosive growth of their embryos. Their
diet, however, appears little different from that of many
other cockroaches.
Reduced Fecundity
One of the most significant costs exacted by carrying egg
cases lies in terms of fecundity. Oviparous type A cockroaches
have relatively high reproductive rates because
the interval between successive oothecae is short, usually
much shorter than the period of incubation. Females typically
produce a second egg case long before the first laid
hatches. Oviparous species with external egg retention as
well as ovoviviparous females produce relatively few
oothecae because oocytes do not mature in the ovaries
while an ootheca is being carried. Viviparity is particularly
expensive, in that female D. punctata have fewer eggs
per oothecae, produce fewer oothecae per lifetime, and
have a longer period of gestation than any other blaberid
(Roth and Stay, 1961; Roth, 1967d). Consequently, the
number of egg cases per lifetime decreases and the oviposition
interval increases in the order oviparous, ovoviviparous,
viviparous (Fig. 7.9) (Willis et al., 1958; Roth and
Stay, 1959, 1962a; Breed, 1983).
Fecundity also appears reduced in cockroach species
that exhibit parental care, particularly if the care involves
feeding young dependents on bodily fluids. Such pabulum
may be demanding in terms of the structures involved
in its manufacture, the nutrients incorporated into
the secretions, and the energy required to produce them.
Fig. 7.9 Frequency of oviposition by individuals of different
species of cockroach. Each dot represents the formation of an
ootheca; the length of the line is the adult lifespan of the female.
Symploce pallens ( hospes) and Supella longipalpa (Blattellidae)
are oviparous and drop the ootheca shortly after it is
formed. Blattella germanica and B. vaga (Blattellidae) carry
their ootheca externally until the eggs hatch. The blaberids
Pycnoscelus surinamensis (parthenogenetic) and Nauphoeta
cinerea are ovoviviparous, and Diploptera punctata is viviparous.
After Roth (1970a).
128 COCKROACHES