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

Table 7.2. Changes in wet weight, water, and solids of cockroach
eggs during embryogenesis (Roth and Willis, 1955a).
closure of the dorsal body wall occurs at 19% of gestation,
after which the embryos begin feeding on maternal secretions
(Stay and Coop, 1973). Dorsal closure occurs at
46% of gestation time in R. maderae (Aiouaz, 1974), at
50% of gestation in N. cinerea (Imboden et al., 1978), and
at 56% of gestation in P. americana (Lenoir-Rousseaux
and Lender, 1970). Gestation of D. punctata embryos
takes 63 days at 27C (Stay and Coop, 1973); nymphs require
just 43 to 52 days to become adults (Willis et al.,
1958).
As might be expected of a group of embryos competing
for food in a limited space, fewer eggs incubated by
the mother results in larger nymphs. This was shown experimentally
by Roth and Hahn (1964), who reduced the
size of the litter in D. punctata by surgically removing one
of the ovaries. Neonates in these broods were larger than
those of control families, presumably because of the
greater amount of nutritive material made available to
the fewer developing embryos. In ovoviviparous N.
cinerea, R. maderae, and Eublaberus posticus, however, the
size of nymphs remains constant regardless of the number
of incubated eggs (Roth and Hahn, 1964; Darlington,
1970). Nymphs within the same ootheca of D. punctata
also can differ considerably in size depending on their position
during development; embryos that have poor contact
with the wall of the brood sac have less ready access
to the nutritive secretion provided by the mother (Roth
and Hahn, 1964). Neonate size, in turn, influences the
number of stadia required to reach adulthood, the developmental
response of individuals to their social environment,
final adult size, and male sexual performance
(Woodhead, 1984; Holbrook and Schal, 2004).
PARTHENOGENESIS
Factors by which initial weights
change, per egg
Species Wet weight Water Solids
Blatta orientalis 1.21 1.35 0.96
Blattella vaga 1.12 1.32 0.81
Blattella germanica 1.21 1.49 0.74
Nauphoeta cinerea 2.11 4.62 0.81
Diploptera punctata 73.47 85.80 49.28
In a number of cockroach species, females are known to
switch to an asexual mode of reproduction when isolated
from males. The resultant offspring are always females,
that is, these cockroaches display facultative thelytokous
parthenogenesis. The phenomenon is known in Blatta
orientalis, B. germanica, Byr. fumigata, E. lapponicus, E.
pallidus, N. cinerea, P. americana, P. fuliginosa, Polyphaga
saussurei, and Su. longipalpa (Roth and Willis, 1956;
Barth, in Roth and Stay, 1962a; Brown, 1973a; Xian,
1998). Not all females of N. cinerea can reproduce by
parthenogenesis; only those with a high level of heterozygosity
are capable, and the ability tends to run in
families (Corley et al., 2001). Parthenogenesis is rather
common in P. americana, and can persist through two
generations in the laboratory (Roth and Willis, 1956).
Asexual reproduction, however, is clearly a fallback strategy
that results in significantly reduced fitness in comparison
to mated females. Nauphoeta cinerea virgins produce
10-fold fewer offspring than mated females, and
nymphs are less viable, take longer to develop, have
shorter adult life spans, and produce fewer offspring of
their own when mated (Corley and Moore, 1999). Asexually
produced oothecae, embryos, and hatched nymphs
are often visibly deformed (Griffiths and Tauber, 1942a;
Roth and Willis, 1956; Xian, 1998), and in Ectobius, few
nymphs develop beyond the second instar (Brown,
1973a). Although the chromosome numbers of asexually
produced embryos of N. cinerea ranged from 2n 19 to
40, only those with the karyotype typical of the species
(2n 36) completed development to the hatching stage
(Corley et al., 1999). Extreme variation in embryonic development
within an ootheca can cause failure of the entire
clutch. If few eggs develop, nymphs may be trapped
in the oothecal casing, as hatch seems to require a group
effort even in the thin, membranous oothecae of ovoviviparous
cockroaches (Roth, 1974b).
Two cockroach species are known to be exclusively
parthenogenetic. The best known is the cosmopolitan
Surinam cockroach, Pycnoscelus surinamensis. This taxon
is the asexual form of its sibling species Pyc. indicus (Roth,
1967b), and includes at least 21 diploid clones derived independently
from sexual females and 11 triploid clones
produced by backcrosses between clones and Pyc. indicus.
There are more than 10 clones of Pyc. surinamensis in the
southeastern United States alone (Roth and Cohen, 1968;
Parker et al., 1977; Parker, 2002). In laboratory experiments
females of Pyc. surinamensis tended to resist the
overtures of male Pyc. indicus, but a few did mate and
sperm transfer was successful. In these, the oocytes matured
at the same rate as in virgins. Fertility was reduced,
however, and all of the resultant offspring were female
(Roth and Willis, 1961). In the bisexual Pyc. indicus, the
oocytes of virgins develop slightly more slowly than those
of mated females, but the proportion of oocytes that mature
is the same. The oothecae, however, are almost always
dropped without being retracted into the brood sac (Roth
and Willis, 1961). Sperm in the spermathecae are re-
REPRODUCTION 121