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

the South American frog Phyllomedusa iheringii indicates
that cockroaches are a major part of its diet (Lagone,
1996). Blattellid cockroaches of the genus Parcoblatta are
a high proportion of the menu of endangered red-cockaded
woodpeckers (Picoides borealis) in the Coastal Plain
of South Carolina (Horn and Hanula, 2002). Cockroaches
were consistently taken by all observed birds,
made up 50% of the overall diet, and were 69.4% of the
prey fed to nestlings (Hanula and Franzreb, 1995; Hanula
et al., 2000). Pycnoscelus indicus on Cousine Island in the
Seychelles is the favored prey of the endangered magpie
robin (Copsychus sechellarum) (S. Le Maitre, pers. comm.
to LMR); the birds feed on American cockroaches as well.
Attempts to control urban infestations of Periplaneta
americana with toxic insecticides may have contributed
to the decline of this species on Frégate Island. The birds
feed close to human habitations and take advantage of
dead and dying insecticide-treated cockroaches. Lethal
doses accumulated in the birds, with subacute effects on
their behavior. The current use of juvenile hormone
analogs for cockroach control appears to result in good
control of the pests while posing a negligible hazard to the
birds (Edwards, 2004). These few examples (see Roth and
Willis, 1960 for more) suffice to emphasize that in their
role as prey, cockroaches may significantly influence the
population structure of insectivores in terrestrial ecosystems.
They may also be a link between terrestrial and
aquatic food chains at river and stream edges, and in delicately
balanced cave ecosystems. Cave-dwelling cockroaches
accidentally introduced into water are one of the
Fig. 10.4 Scorpion feeding on the ground-dwelling cockroach
Homalopteryx laminata, Trinidad. Photo courtesy of Betty
Faber.
principal foods of some cavernicolous fishes; they are
26% of the diet of Milyeringa veritas (Humphreys and
Feinberg, 1995). Cockroaches are considered the base of
the food web in South African bat caves and support a
large community of predators and parasites. Their feces
are also an important food source for smaller invertebrates
(Poulson and Lavoie, 2000). Hill (1981) noted that
for most of the guano community in Tamana cave,
Trinidad, the incoming supply of energy was in the form
of cockroach, not bat, feces.
At the top of the food chain, there are numerous reports
of cockroaches preying on other insects (detailed by
Roth and Willis, 1960). Most of these accounts are observations
of opportunistic predation on a broad range of
vulnerable taxa and life stages, particularly eggs and larvae.
Instances of cockroaches controlling prey populations
of crickets and bedbugs in urban settings are frequent
in the historic literature but largely anecdotal and
unverified. One ecological setting in which cockroaches
do have potential for influencing population densities of
prey is in caves (Chapter 4).
LARGE-SCALE EFFECTS
Cockroaches potentially influence biogeochemical cycles
via two known pathways: nitrogen fixation and methane
production. Cryptocercus is the only cockroach currently
known to harbor gut microbes capable of fixing atmospheric
nitrogen (Breznak et al., 1974), but spirochetes
found in the hindgut of other species also may have the
ability (Lilburn et al., 2001). Acetylene reduction assays
indicate that adults and juveniles of Cryptocercus fix nitrogen
at rates comparable to those of termites on a body
weight basis (0.01–0.12 mg N day 1 g 1 wet weight)
(Breznak et al., 1973; Breznak et al., 1974, 1975). The
process provides a mechanism for nitrogen return to the
ecosystem and may have a significant ecological impact
(Nardi et al., 2002), particularly in the food chains of the
montane mesic forests where Cryptocercus is the dominant
macroarthropod feeding in rotting logs.
A more universal characteristic of cockroaches is an association
with methanogenic bacteria in the hindgut and
the consequent emission of methane. Almost all tropical
cockroaches tested emit methane, regardless of the origin
of specimens and their duration of laboratory captivity.
Methane, carbon dioxide, and water are released synchronously
in a resting cockroach, in slow periodic cycles
that suggest the gases are respired (Bijnen et al., 1995,
1996). Among temperate species, North American C.
punctulatus emits the gas (Breznak et al., 1974), but
the European genus Ectobius does not (Hackstein and
Strumm, 1994). Cockroaches (n 34 species) produce
an average of 39 nmol/g methane/h, with a maximum of
ECOLOGICAL IMPACT 171