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

duct and is pressed by the male’s endophallus against the
female genital sclerites (Khalifa, 1950). In Periplaneta the
spermatophore is not discharged until at least an hour
from the beginning of copulation (Gupta, 1947). In N.
cinerea, where copulation length is typically short, mating
pairs detached after 10–12 min can be separated into
three groups. In some, only a copious secretion is present;
in others a spermatophore has been transferred but is not
secured. A third group has a spermatophore firmly inserted
(Roth, 1964b).
Three spermatophore layers can be distinguished in
Blattella: a clear, transparent section covering the ventral
surface, a lamellated portion that forms the dorsal wall,
and at its core, suspended in a milky white mass, are two
sacs containing the sperm (Khalifa, 1950). Periplaneta’s
spermatophore has just one sperm sac (Jaiswal and
Naidu, 1976). In Blaberus craniifer the spermatophore
consists of four heterogeneous layers, and is invested with
a variety of enzymes including proteases, esterases, lipases,
and phosphatases (Perriere and Goudey-Perriere,
1988). Several mechanisms exist for fixing the spermatophore
in the female (Graves, 1969): (1) the soft outer
layer hardens against the female genital sclerites (Blattinae);
(2) a thick, wax-like shell holds it in place (most
Blattellidae); (3) a large quantity of glue-like secretion secures
it (Blaberinae, one Zetoborinae); (4) a uniquely
shaped, elongated spermatophore is enclosed in a large
membranous bursa copulatrix in the female (Diplopterinae,
Oxyhaloinae, Panchlorinae, Pycnoscelinae, one Zetoborinae).
When transferring the spermatophore, the male orients
its tip so that the openings of the sperm sacs are
aligned directly with the female spermathecal pores
(Khalifa, 1950; Roth and Willis, 1954b; Gupta and Smith,
1969); this is apparently unusual among insects (Gillott,
2003). The sperm do not migrate from the spermatophore
until copulation is terminated. When first transferred,
the spermatophore of N. cinerea contains nonmotile,
twisted sperm; they became active about 2 hr later.
Two to three days after mating only a few sperm remain
in the spermatophore but the spermathecae are densely
filled with them (Roth, 1964b; Vidlička and Huckova,
1993). If the spermatophore is removed 25 min after the
male and female detach in B. germanica, “a thin thread of
spermatozoa, hair-like in appearance, may extend from
the female’s spermathecal opening” (Roth and Willis,
1952a). It takes about 5 hr for sperm to migrate into the
spermathecae of D. punctata (Roth and Stay, 1961). The
stimulus for sperm activation may be in male accessory
gland secretions transferred along with the sperm (Gillott,
2003), produced by the female in the spermathecae
or spermathecal glands (Khalifa, 1950; Roth and Willis,
1954b), or both. Little is known regarding the mechanism
by which sperm move from the spermatophore to the
spermatheca. Among the nonexclusive hypotheses are the
active motility of sperm, migration in chemotactic response
to spermathecal or spermathecal gland secretions,
contractions of visceral muscles associated with the female
genital ducts, and aspiration by pumping movements
of the musculature of the spermatheca (Gupta and
Smith, 1969). Male accessory gland secretions may play a
role in stimulating female muscle contraction (Davey,
1960). The activity and morphology of sperm may
change once they reach the spermatheca. In Periplaneta,
alterations were noted chiefly in the acrosome (Hughes
and Davey, 1969).
Sperm Morphology
Cockroaches have extremely thin sperm, with long, actively
motile flagellae (Baccetti, 1987). The sperm head
and the tail are indistinguishable in some species, such as
B. germanica, but can be distinct and variable among
other examined cockroaches. The sperm head in Arenivaga
boliana, for example, is helical, and that of Su. longipalpa
is extremely elongated (Breland et al., 1968). Total
sperm length varies considerably, with B. germanica and
P. americana at the extremes of the range in 10 examined
cockroach species (Breland et al., 1968). The limited data
we have suggest that body size and sperm length may be
negatively correlated (Table 6.1), but the relative influences
of body size, cryptic choice mechanisms, and sperm
competition have not been studied.
Dimorphic sperm have been described in P. americana
(Richards, 1963). A small proportion are “giants,” sperm
that have big heads and tails that are similar in length but
two or more times the diameter of typical sperm. These
chunky little gametes swim at approximately the same
speeds as the “normal,” more streamlined, sperm, and are
thought to be the result of multinucleate, diploid, or
Table 6.1. Sperm length relative to body length in cockroaches.
Sperm data from Jamieson (1987) and Vidlička and Huckova
(1993).
Approximate 1 Sperm Ratio body
body length length length:sperm
Species length (mm) (µ) length
Blattella germanica 12.0 450 27:1
Pycnoscelus indicus ~ 21.0 2 250 84:1
Nauphoeta cinerea 27.0 300 90:1
Periplaneta americana 37.5 85 441:1
Blaberus craniifer 55.0 180 306:1
1
Body length can range fairly widely within a species, for example, male
B. germanica ranges from 9.6 to 13.8 mm in length (Roth, 1985).
2
Body length based on its sibling species, Pyc. surinamensis.
94 COCKROACHES