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

americana, and are thought to have a structural and protective
function (Stay et al., 1960; Rajulu and Renganathan,
1966), just as they do in plants that possess
them (Hudgins et al., 2003). The oothecal casing is thinner
and less rigid in species that externally carry the egg
case (oviparous type B); calcium oxalate crystals are
sparse in both B. germanica and Loph. brevis (Roth,
1968b). Ovoviviparous type A cockroaches typically produce
a thin, soft, lightly colored ootheca that lacks a keel
and which in some species only partially covers the eggs,
particularly in later stages of gestation (Roth, 1968a) (Fig
7.5A); calcium oxalate is absent. This type of egg case is
produced by Blaberidae and also Sliferia, one of few Blattellidae
that retract their ootheca into a brood sac (Stay et
al., 1960; Roth, 1968a). The nature of the ootheca, then,
changes in parallel with stages of internalization of the
egg case. It goes from having a rigid outer casing in those
species that abandon the egg case, to a flexible, soft membrane
in those that have internalized it. It has intermediate
properties in those cockroaches that carry the ootheca
externally during gestation, and has been completely lost
in one derived lineage (Geoscapheini: ovoviviparous type
B) (Roth and Willis, 1958a; Roth, 1968a, 1970a). Females
exhibit a parallel regression of the morphological structures
associated with oothecal production (reviewed by
Nalepa and Lenz, 2000).
Oviparous cockroaches in protected environments,
like social insect nests, also may exhibit reduction or loss
of the egg case. The ootheca of Attaphila fungicola, for example,
lacks a keel (Roth, 1971a), and several species of
Nocticolidae have thin, transparent oothecal cases. Nocticola
termitophila apparently lays its eggs singly, without
any external covering (Roth, 1988). Termites, the “social
cockroaches” (Chapter 9), exhibit a parallel loss of protective
egg cases. The basal termite Mastotermes darwiniensis
packages its eggs within a thin, flexible outer
covering that lacks keel. The site and mode of production,
associated morphological structures in the female, parallel
arrangement of eggs, and discrete, tanned outer covering
together indicate that the ootheca of Mastotermes is
homologous with those of cockroaches (Nalepa and
Lenz, 2000). All other termites lay their eggs singly, without
a covering. Both the heart of a social insect colony and
the brood sacs of live bearing cockroaches are moist, protected
sites for incubating eggs, allowing for the reduction
and eventual elimination of defensive structures in evolutionary
time. The oothecal case is 86–95% protein
(Table 4.5), so “it is no wild supposition that in the course
of time the chitinous ootheca, being in these species a
work of supererogation, will disappear” (Shelford, 1912b).
Perhaps the main reason that the ootheca has not been
completely eliminated in most ovoviviparous cockroaches
is because it determines the orderly arrangement of eggs
and therefore assures contact and exchange of water and
other materials between each egg and the wall of the
brood sac (Rugg and Rose, 1984b). A study of the Geoscapheini
whose eggs are incubated in a disordered mass
in the brood sac (Rugg and Rose, 1984c) (Fig. 7.5B) is the
logical focal group for testing this hypothesis.
Selective Pressures
Most hypotheses offered to explain why live bearing has
evolved in animals invoke agents affecting offspring viability
as the selective pressure for an evolutionary shift in
reproductive mode. Costs that accrue to mothers then either
facilitate or constrain the transition. These may include
reduced maternal mobility, with consequences for
foraging efficiency and predator evasion, reduced fecundity,
and the increased metabolic demands of carrying
offspring throughout their development (Shine, 1985;
Goodwin et al., 2002, among others). It is difficult, however,
to use present-day characteristics of ovoviviparous
or viviparous organisms as evidence for hypotheses on
the evolution of these traits, as current habitats may be
different from the habitats in which the reproductive
modes first evolved (Shine, 1989). It is also important to
note that each strategy has its benefits and liabilities in a
given environment. Oviparity is not inherently inferior to
ovoviviparity or viviparity just because it is the ancestral
state. The problem of water balance in cockroaches, for
example, is handled by each reproductive mode in different
ways, each of which may be optimal in different habitats.
Egg desiccation can be minimized if: (1) the ootheca
is deposited in a moist environment, (2) the ootheca has
a waterproofing layer, or (3) the female dynamically
maintains water balance while the egg case is externally
attached or housed in a brood sac (Roth, 1967d).
Increased Offspring Viability
McKittrick (1964) was of the opinion that the burial and
concealment of oothecae by oviparous females is a response
to pressure from parasitoids and cannibals. Although
few studies directly address this question, some
evidence suggests that concealing oothecae may attract
rather than deter hymenopterous parasitoids. The mucopolysaccharides
in the saliva used to attach egg cases to
the substrate may act as kairomones, making oothecae
more vulnerable to attack. Parasitic wasps may even expose
buried oothecae by digging them out from their
protective cover (Narasimham, 1984; Vinson and Piper,
1986; Benson and Huber, 1989). On the other hand,
oothecae of P. fuliginosa that were glued to a substrate had
a higher eclosion rate than those that were not glued, suggesting
that salivary secretions may enhance egg viability
in some unknown way (Gordon et al., 1994). Oothecae of
126 COCKROACHES