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

glion but require a longer period to reach the brain, or
that there is another source of stimulation in the genital
region. If firmly inserted spermatophores are removed
from mated females, about 15% will mate again (Roth,
1964b). After copulation, females remain unreceptive until
after partition, at which time most remate. The absence
of sperm in the spermatheca does not influence the return
of receptivity after the first oviposition (Roth, 1962,
1964a, 1964b).
Mating Plugs
In cockroaches, the physical presence of a spermatophore
in the genital tract of a female may play a dual role in preventing
sperm transfer from other males. Besides acting
as mechanical triggers in turning off female receptivity,
they may also serve as short-term physical barriers to the
placement of additional spermatophores. Copulating
males typically deposit spermatophores directly over the
spermathecal openings. If a female accepts an additional
male and a second spermatophore is inserted, it is doubtful
that the second male’s sperm could access female
sperm storage organs. Additional spermatophores are
usually improperly positioned (Roth, 1962; Graves, 1969).
Spermatophore shape and its mechanism of attachment
vary among cockroach taxonomic groups and some types
are probably more refractory to dislodgment than others.
In some blaberids the spermatophore has a dorsal groove
that fits closely against the female genital papilla (Graves,
1969). In blattellids with uricose glands, uric acid deposited
on the spermatophore can fill the genital atrium
of the female (Roth, 1967c).
The spermatophore is discarded by the female after
20–24 hr in P. americana (Jaiswal and Naidu, 1976), after
2–3 days in Blatta orientalis (Roth and Willis, 1954b), after
4–9 days in Eub. posticus (Roth, 1968c), by the 5th day
in Blab. craniifer (Nutting, 1953b), by the 6th day in D.
punctata (Engelmann, 1960), and after 6–13 days in R.
maderae (Roth, 1964b). Young females of N. cinerea extrude
the spermatophore after 5 or 6 days, but older females
may retain it for over a month (Roth, 1964b). The
mechanism by which cockroach females eject the spermatophore
is not altogether clear. In B. germanica, the
spermatophore remains in place about 12 hr and then
shrinks; the shriveled remains may adhere to the female
for several days (Roth and Willis, 1952a). Jaiswal and
Naidu (1976) indicate that shrinkage of the outermost
layer also causes spermatophore separation in P. americana,
but Hughes and Davey (1969) thought that it disintegrated
as a result of exposure to spermathecal secretions.
Disintegration of the spermatophore is also
reported in Blab. craniifer (Hohmann et al., 1978). A secretion
from the spermathecal glands apparently facilitates
spermathecal extrusion in four examined Blaberidae
(D. punctata, R. maderae, N. cinerea, Byr. fumigata).
The secretion is under the control of the corpora allata,
and loosens the spermatophore by softening the material
covering it (reviewed by Roth, 1970b). Nonetheless, a few
experimental females of R. maderae were able to extrude
their spermatophores despite surgical removal of the
spermathecal glands (Engelmann, 1957).
Mechanical Stimulation and “Imposed Monogamy”
Roth’s (1964b) demonstration that the suppression of female
receptivity results from the physical insertion of the
spermatophore into the bursa in N. cinerea has been interpreted
as evidence that males force monandry on females
during their first reproductive cycle. The bursa and
the brood sac are in close physical proximity within the
female genital tract. This serves as the basis for the
argument that males are co-opting the physiological
mechanism evolved to suppress female receptivity during
pregnancy, and so females are precluded from evolving
countermeasures to this manipulation (Harris and
Moore, 2004; Montrose et al., 2004). Several points must
be carefully considered before accepting this interpretation.
First, while the brood sac is spatially proximate to the
genital papilla on which the spermatophore is secured,
there is no evidence that the two structures share a mechanism
for suppressing female receptivity. The highly distensible
brood sac is situated at the anterior end of the
vestibulum. It is separated from the genital papilla by the
laterosternal shelf (McKittrick, 1965) (Fig. 6.14A). When
the female is incubating an ootheca, the genital papilla is
forced to stretch as the egg case projects into the vestibulum
(Fig. 6.14B). Nonetheless, engaging the mechanoreceptors
in the brood sac of a virgin has little to no effect
on her receptivity. When glass beads were inserted into
the brood sac without applying pressure to the bursa,
72% of virgins subsequently mated. Some physiological
change occurs after ovulation that makes females responsive
to inhibitory stimuli from the stretched brood sac
(Roth, 1964b, p. 925). The loss of receptivity after the first
copulation of her adult life, and the loss of receptivity in
response to an ootheca stretching the brood sac, then, do
not have a shared control mechanism.
Second, the imposed monogamy scenario is predicated
on the assumption that multiple copulations within the
first reproductive cycle confer benefits on female N. cinera.
In many insects, females profit from multiple matings
because they can increase fitness via increased egg production
and fertility (Arnqvist and Nilsson, 2000). A
male, on the other hand, benefits by rendering females
sexually unreceptive after mating, thus increasing the
probability that his sperm will fertilize the majority of
the female’s eggs (Cordero, 1995; Eberhard, 1996; Gillott,
108 COCKROACHES