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

Fig 7.8 Parasitism of cockroach eggs. (A) Anastatus floridanus
ovipositing into an ootheca carried by Eurycotis floridana. (B)
Detail of oviposition by the parasitoid. Photos by L.M. Roth
and E.R. Willis.
oviparous cockroaches are also prone to parasitism prior
to deposition, while females are forming and carrying
them. The window of vulnerability can be a wide one. Females
of Nyc. acaciana, for example, can take 72 hr to
form an ootheca (Deans and Roth, 2003). The parasitoid
Anastatus floridanus (Eupelmidae) oviposits in egg cases
attached to female Eur. floridana (Fig. 7.8) (Roth and
Willis, 1954a). The cockroach can detect the presence of
the wasp on the surface of the ootheca and tries to dislodge
it with her hind legs (LMR, pers. obs.). Blattella spp.
that carry egg cases externally until hatch are also vulnerable
to egg parasitoids, and continue to carry the parasitized
ootheca (Roth, 1985). External retention of egg
cases, then, may be little better than concealment in conferring
protection from parasitism.
The value of egg case burial lies primarily in protecting
them from predation and cannibalism; concealment is almost
100% effective in saving oothecae from being devoured
by other cockroaches (Rau, 1940). McKittrick et
al. (1961) found that in Eur. floridana, burial of oothecae
prevented cannibalism by conspecifics and predation by
ants, carabids, rodents, and other predators. Conversely,
exposed egg cases and those still attached to a female are
subject to biting and cannibalism (Roth and Willis,
1954b; Willis et al., 1958; Gorton, 1979). These improprieties
are countered with aggression on the part of the
mother. Female P. brunnea, P. americana, and Paratemnopteryx
couloniana drive other females away from exposed
oothecae (Haber, 1920; Edmunds, 1957; Gorton,
1979). Two behavioral classes of female can be distinguished
in B. germanica; females carrying oothecae are
more aggressive than females that had not yet formed
them (Breed et al., 1975). Aggressive behavior is favored
despite its attendant risks, given that one nip taken from
an ootheca can result in the death of the entire clutch
from desiccation (Roth and Willis, 1955b).
Ovoviviparity is viewed as a solution to this constant
battle against predators and parasites, and is thought to
have appeared in the Mesozoic as an evolutionary response
to cockroach enemies that first appeared during
that time (Vishniakova, 1968). Parasitoids have not been
detected in the oothecae of ovoviviparous blaberids
(LMR, pers. obs.). The eggs are exposed to the environment
for only the brief period of time between formation
of the ootheca and its subsequent retraction into the
body, allowing only a narrow time frame for parasitoid
oviposition. Once in this enemy free space, the eggs are
subject only to “the vicissitudes that beset the mother”
(Roth and Willis, 1954b). Nonetheless, nymphs of ovoviviparous
cockroaches are at risk from cannibalism at the
time of hatch. Attempts by conspecifics to eat the hatchlings
as the female ejects the ootheca have been noted and
may include pulling the still attached egg case away from
the mother (Willis et al., 1958). We note, however, that
laboratory observations of cannibalism in cockroaches of
any reproductive mode may be of little consequence in
natural populations, with the exception of highly gregarious
species like cave dwellers. Females of at least one
species of the latter are known to be choosy about where
they expel their neonates. Darlington (1970) reported
that pregnant females of Eub. posticus preferred one
chamber of the Tamana cave for giving birth, and migrated
into that chamber from other parts of the cave.
Defense against pathogens as agents of egg mortality is
unstudied, despite the disease-conducive environments
typical of cockroaches.
Parental Costs
Indirect reproductive costs of oviparity in cockroaches
include the time, energy, and predation risks involved in
concealing the ootheca in the environment and the metabolic
expense of producing a protective oothecal case.
The case consists primarily of quinone-tanned protein
(Brunet and Kent, 1955) (Table 4.5), much of which can
be recovered after hatch if the parent or neonates eat the
embryonic membranes, unviable eggs, and the oothecal
case after hatch (Roth and Willis, 1954b; Willis et al.,
1958). In several species of cockroaches, oothecal predation
by adults and the ingestion of oothecal cases after
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