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

sites in the clay wall of a terrarium (Deleporte, 1985), and
Pyc. surinamensis can excavate tunnels that extend up to
13 cm beneath the soil surface. These tubes may end in a
small chamber where juveniles molt and females bear
young (Roesner, 1940). At least two unstudied blaberids
in the subfamily Perisphaeriinae appear to live in permanent
soil burrows. Female Cyrtotria ( Stenopilema) are
found in a burrows surrounded by juveniles (Shelford,
1912b). Similarly, a female Pilema thoracica accompanied
by several nymphs was taken from the bottom of a neat
round hole about 15 cm in depth; there were about a
dozen such holes in half an acre and all contained families
of this species (Shelford, 1908). Cockroaches of a
Gromphadorhina sp. have been observed in a ground burrow
in grassland of the Isalo National Park in Madagascar.
The heads and antennae of both adults and nymphs
were projecting from the entrance, which was about 5 cm
in diameter (G. Alpert, pers. comm. to LMR).
All other cockroaches that form permanent burrows
in compacted soil belong to four Australian genera of
the subfamily Panesthiinae: Macropanesthia, Geoscapheus,
Neogeoscapheus, and Parapanesthia (Roth, 1991a). They
are distributed mainly east of the Great Dividing Range
with a concentration in southeast Queensland (Roach
and Rentz, 1998). The giant burrowing cockroach M. rhinoceros
is the best studied (Rugg and Rose, 1991; Matsumoto,
1992), but the biology of the other species is similar
(D. Rugg, pers. comm. to CAN). All feed on dry plant
litter that they drag down into their burrows. Burrow entrances
have the characteristic shape of a flattened semicircle,
but may be slightly collapsed or covered by debris
during the dry season. Tunnels initially snake along just
beneath the soil, then spiral as they descend and widen
out; they tend to get narrow again at the bottom. Litter
provisions are typically stored in the wider part, and the
cockroaches retreat to the narrow blind terminus when
alarmed. They are not known to clean galleries; consequently,
debris and excrement accumulate (Rugg and
Rose, 1991; D. Rugg, pers. comm. to CAN). Species distribution
is better correlated with soil type than with vegetation
type. Burrows of M. rhinoceros may be found in Eucalyptus
woodland, rainforest, or dry Acacia scrub, as long
as the soil is sandy. Other species are associated with gray
sandy loams, red loam, or hard red soil (Roach and Rentz,
1998). The depth of Macropanesthia saxicola burrows is
limited by the hard heavy loam of their habitat, and those
of M. mackerrasae tend to be shallow and non-spiraling
because they run up against large slabs of rock. The deepest
burrows are those of females with nymphs, the shallowest
are those of single nymphs (Rugg and Rose, 1991;
Roach and Rentz, 1998). Female M. rhinoceros reproduce
once per year, and nymphs remain in the tunnel with
females for 5 or 6 mon before they disperse, initiate
their own burrows, and begin foraging. These mid-size
nymphs then enlarge their burrows until adulthood. Development
requires a minimum of 2 or 3 yr in the field,
but growth rates are highly variable. Adults live an additional
6 yr (Rugg and Rose, 1991; Matsumoto, 1992).
Males are occasionally found in the family during early
stages of the nesting cycle. Both sexes emerge from burrows
after a rainfall, with females foraging and males
looking for females. Surface activity in M. rhinoceros occurs
from just before midnight to a couple of hours after
sunrise; peak of activity is 2 or 3 hr before sunrise. Small
nymphs are never observed above ground (Rugg and
Rose, 1991).
Recent evidence indicates that among the Panesthiinae,
the ecological and evolutionary boundaries between
the soil-burrowing–litter-feeding habit, and one of living
in and feeding on wood, are more fluid than expected. In
1984, Rugg and Rose (1984c) proposed that the soil-burrowing
cockroaches be elevated to the rank of subfamily
(Geoscapheinae) on the basis of their unique reproductive
biology. Recently, however, a molecular analysis of
three genes from representatives of nine of the 10 Panesthiinae
and Geoscapheini genera by Maekawa et al.
(2003) indicates that these taxa form a well-supported
monophyletic group, with the former paraphyletic with
respect to the latter (Fig. 2.13). These authors propose
that the ancestors of soil-burrowing cockroaches were
wood feeders driven underground during the Miocene
and Pliocene, when dry surface conditions forced them to
seek humid environments and alternative sources of
food. This suggestion is eminently reasonable, as there are
isolated cases of otherwise wood-feeding cockroach taxa
collected from soil burrows or observed feeding on leaf
litter. Ancaudellia rennellensis in the Solomon Islands lives
in underground burrows (Roth, 1982b), even though the
remaining species in the genus are wood feeders. There is
also a record of a male, a female, and 19 nymphs of
Panesthia missimensis in Papua New Guinea collected
0.75 m deep in clay, although others in the species were
collected in rotten logs (Roth, 1982b). Although the preferred
habitat of the endangered Panesthia lata is decaying
logs, Harley Rose (University of Sydney) has also
found them under rocks, sustaining themselves on Poa
grass and Cyperus leaves (Adams, 2004). Even individuals
or small groups of C. punctulatus are sometimes found in
a small pocket of soil under a log, directly beneath a
gallery opening (Nalepa, 2005), particularly when logs
become dry. These examples are evidence that the morphological
adaptations for burrowing in wood also allow
for tunneling in soil, and that the digestive physiology of
wood-feeding Panesthiinae may be flexible enough to al-
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