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

direct sunlight. In species that leave oothecae exposed, the
egg case may be cryptically colored. Shelford (1912b) described
the ootheca of an unknown species from Ceylon
(now Sri Lanka) that was attached to the upper surface of
a leaf. It was white, mottled with brown, and looked “singularly
like a drop of bird’s excrement.”
External Egg Retention
Fig. 7.2 The diurnal Australian cockroach Polyzosteria mitchelli
digging a hole for hiding her ootheca. It is a beautiful
species, with a bronze dorsal surface spotted and barred with
orange or yellow, a pale yellow ventral surface, and sky-blue
tibiae. The lively colors fade after death. Photo by E. Nielsen,
courtesy of David Rentz.
glue the ootheca in a precise position inside it, then conceal
it with bits of debris, pieces of the substrate, or excrement
(Fig. 7.2). Ootheca concealment is known in
blattids (e.g., Blatta orientalis, Eurycotis floridana,
Methana marginalis, Pelmatosilpha purpurascens, Periplaneta
americana, P. australasiae, P. brunnea, P. fuliginosa),
blattellids (Ectobius sylvestris, Parcoblatta pennsylvanica,
Supella longipalpa, Loboptera decipiens, Ellipsidion
affine, Ell. australe), and cryptocercids (Cryptocercus
punctulatus). In the latter, wood and saliva are used to
pack oothecae into slits carved in the ceilings of their
wood galleries; the keels of the oothecae are left uncovered
(Nalepa, 1988a). Concealment behavior may vary
among closely related cockroach species. Female Ectobius
pallidus, for example, carefully bury their oothecae after
deposition; E. lapponicus and E. panzeri seldom do
(Brown, 1973a). Intraspecific variation in this behavior
may depend to some extent on the substrate on which the
insects are found or maintained. Nyctibora noctivaga simply
drops its ootheca in the laboratory, but in Panama,
oothecae were found glued to leaves and in crevices of the
piles supporting a house (McKittrick, 1964). Although
females whose eggs absorb water from the substrate have
to be exceptionally discriminating in where they place
oothecae, they do not always make wise choices. In five
species of Parcoblatta, it is common to find shrunken
oothecae, as well as oothecae that have burst and extruded
material from the keel (Cochran, 1986a). A great
many unhatched and shriveled oothecae of Parc. pennsylvanica
were found under the bark of pine logs in an early
stage successional forest by Strohecker (1937); mortality
was attributed to the high temperature of logs exposed to
In cockroaches displaying oviparity type B, the egg cases
are carried externally for the entire period of embryogenesis
with the end of the ootheca closely pressed to the
vestibular tissues of the female’s genital cavity. The proximal
end of the egg case is permeable, allowing for transport
of water from the female to the developing eggs
(Roth and Willis, 1955b, 1955c; Willis et al., 1958). Recently,
Mullins et al. (2002) injected radiolabeled water
into female Blattella germanica carrying egg cases. The
water was detected moving from the female to the proximal
end of her ootheca, then spreading throughout the
egg case following a concentration gradient (Fig. 7.3). A
variety of water-soluble materials were also transferred
across the female-ootheca divide, including glucose, leucine,
glycine, and formate. Preliminary experiments of
these authors indicate that the labeled materials also can
be detected in nymphs after hatch. Scanning electron microscopy
and the use of fluorescent stains pinpointed the
structural basis of flow into the ootheca (Fig. 7.4). Small
pores completely penetrating the oothecal covering are
Fig. 7.3 Distribution of radiolabel in oothecae attached to
Blattella germanica females at four time intervals after injection
of 3 H 2
O into the females. See original paper for sample sizes
and variation. After Mullins et al. (2002), with permission from
The Journal of Experimental Biology. Image courtesy of Donald
and June Mullins.
118 COCKROACHES