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

oach guts, like termite guts (Ohkuma, 2003), may be a
source of novel microorganisms with wide-ranging industrial
applications.
CONSERVATION
Cockroaches are not generally considered a charismatic
taxon; species that are threatened with extinction are unlikely
to rally conservationists to action. They are nonetheless
an integral part of a stable and productive ecosystem
in tropical rainforest and other habitats. Cockroaches
deserve our consideration and respect for the range of
services they perform and for their membership in an
intricate web of interdependent and interacting flora,
fauna, and microbes. Many cockroach species live in
habitats of conservation concern and are threatened by
canopy removal, urbanization, and agricultural practices.
Philopatric species with naturally small population sizes
and specific habitat requirements are particularly vulnerable
to perturbations (Pimm et al., 1995; Tscharntke et al.,
2002; Boyer and Rivault, 2003). These taxa are frequently
wingless, and their consequent low dispersal ability
makes them vulnerable to habitat fragmentation and genetic
bottlenecks. Several species of Australian burrowing
cockroaches have restricted ranges and are affected by
farming/forestry practices or by urbanization. The accompanying
soil disturbance, soil compaction, and loss of
their leaf litter food sources have devastated some populations
of these unique insects (H.A. Rose, pers. comm. to
CAN).
Caves are delicately balanced and vulnerable ecosystems
whose resident cockroaches can be severely affected
by guano compaction, guano collection, and other human
disturbances (Braack, 1989). Nocticola uenoi miyakoensis,
for example, became rare in the largest known
limestone cave on Miyako-jima Island after it was opened
to tourists (Asahina, 1974), and the invertebrate community
of an Australian cave disappeared due to soil compaction
by human visitors (Slaney and Weinstein, 1997a).
According to Gordon (1996), the cave-dwelling species
Aspiduchus cavernicola (Tuna Cave cockroach) living in a
network of caves in southern Puerto Rico is officially
classified as a “species at risk”by the U.S. Fish and Wildlife
Service. Roth and Naskrecki (2003) recently described a
new species of cave cockroach collected during a Conservation
International survey of West African sites under
threat from large-scale mining operations. The removal
of cave cockroaches for scientific study also can have a
significant impact on their populations (Slaney and Weinstein,
1997a).
Global warming and the resultant decrease in snow
cover at high elevations may put cockroaches such as the
New Zealand alpine species Celatoblatta quinquemaculata
at risk (Sinclair, 2001). Although the species is physiologically
protected against the cold, it relies on the thermal
buffering effect of snow cover in particularly harsh
winters. Reduced snow cover results in an increased number
of freeze-thaw cycles and lower absolute minimum
temperatures, making the “mild” winter more, rather
than less, stressful to the insect.
Wood-feeding and other log-dependent cockroaches
(Table 3.2) are sensitive to the ecological changes brought
about by both modern forestry and human settlement
and, like many saproxylic arthropods (Grove and Stork,
1999; Schiegg, 2000), may be used as habitat continuity
indicators in ecological assessment. These insects rely on
a resource whose removal from the ecosystem is the usual
objective of forest management (Grove and Stork, 1999)
and compete with lumber companies (Cleveland et al.,
1934) and resident humans who prize coarse woody debris
as fuel and building material. Wood-feeding cockroaches
may survive canopy removal and subsequent desiccating
conditions if logs of a size sufficient to provide a
suitable microhabitat are left on the ground. Cryptocercus
primarius, for example, has been collected from largediameter
logs in young re-growth forest in China (Fig.
10.5). More often, however, coarse woody debris left on
the forest floor after logging operations is gathered and
used as fuel (Nalepa et al., 2001b). Based on the work of
Harley Rose (University of Sydney), the endemic Lord
Howe Island wood-feeding cockroach Panesthia lata was
recently listed by the New South Wales Scientific Committee
as an endangered species (Adams, 2004). It has not
been found on Lord Howe Island since the 1960s, probably
because of rats introduced in 1918. Small numbers of
the cockroach were recently discovered on Blackburn Island
and Roach Island.
Litter-dwelling cockroaches can be sensitive habitat indicators.
The Russian cockroach Ectobius duskei, normally
found at levels of up to 10 individuals/m 2 in undisturbed
steppe, disappears if these grasslands are plowed
to grow wheat. If the fields are allowed to lie fallow, the
cockroaches gradually become reestablished (Bei-Bienko,
1969, 1970). Although the species has been eliminated in
intensely cultivated areas, a 1999 study found E. duskei
well represented in the leaf litter of steppe meadows in the
Samara district (Lyubechanskii and Smelyanskii, 1999).
The effect of disturbance on litter invertebrates depends
not only on the type of disturbance, but also on
site-specific factors. In the dry Mediterranean-type climate
of western Australia cockroaches appear resilient to
moderate disturbances. Cockroach numbers and species
richness as measured by pitfall traps declined significantly
after logging and fire, yet recovered within 48 mon.
ECOLOGICAL IMPACT 173