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

ingested because they serve as fuel for microbial growth
on the ingested substrate, on feces, and in the gut, and it
is the microbes and their products that are of primary nutritive
importance to the cockroach (Nalepa et al., 2001a).
Fig 5.1 Scanning electron micrograph of the ciliate Nyctotherus
ovalis from the hindgut of Periplaneta americana. Scale
bar 20 m. From van Hoek et al. (1998); photo courtesy of
J. Hackstein, with permission of the journal Molecular Biology
and Evolution.
digestive system, and these enzymes are both endogenous
and microbial in origin (Wharton and Wharton, 1965;
Wharton et al., 1965; Bignell, 1977a; Cruden and Markovetz,
1979; Gijzen et al., 1994; Scrivener and Slaytor,
1994b). The nature of the contribution of cellulose to
cockroach nutritional ecology, however, has been difficult
to determine; in most cases no obvious nutritional benefit
can be detected (Bignell, 1976, 1978), even in some
wood-feeding cockroaches. Zhang et al. (1993), for example,
found that Geoscapheus dilatatus, which feeds on
dead, dry leaves, was able to utilize cellulose and hemicellulose
more efficiently than the wood-feeding species
Panesthia cribrata. The latter was surprisingly inefficient
in extracting both cellulose (15%) and hemicellulose
(3%) from its diet. In omnivorous domestic species, cellulose
digestion may be a backup strategy, to be used
when other available foods are inadequate (Jones and
Raubenheimer, 2001). This is supported by evidence that
solids are retained longer in the gut of starving Periplaneta
americana (Bignell, 1981), allowing more time for
processing the less digestible components. Retention time
in animals with hindgut fermentation is directly related
to digestive assimilation and efficiency (Dow, 1986; van
Soest, 1994). The fact that so many cockroaches feed on
cellulose-based substrates in the field but there is so little
evidence for it playing a significant metabolic role suggests
another possible function: the breakdown of cellulose
may primarily provide energy for bacterial metabolism
(Slaytor, 1992, 2000). Fibrous materials, then, may be
Ontogeny of Microbial Dependence
Although it is often tacitly assumed that hosts derive net
advantage from their mutualists throughout their lifecycle,
in a number of associations it is only at key stages
in the host lifecycle that exploitation of symbionts is important
(Smith, 1992; Bronstein, 1994). Regardless of the
exact nature of the benefits, young cockroaches depend
more than older stages on gut microbiota. If the hindgut
anaerobic community is eliminated, adequately fed
adults are not affected. The overall growth of juvenile
hosts, however, is impeded, and results in extended developmental
periods. The weight of antibiotic-treated P.
americana differed by 33% from controls at 60 days of
age. Defaunation also lowered methane production and
VFA concentrations within the hindgut, and the gut itself
became atrophied (Bracke et al., 1978; Cruden and
Markovetz, 1987; Gijzen and Barugahare, 1992; Zurek
and Keddie, 1996).
The nutritional requisites of young cockroaches also
differ from those of adults (P. americana), and are reflected
in the activities of hindgut anaerobic bacteria, including
methanogens (Kane and Breznak, 1991; Gijzen
and Barugahare, 1992; Zurek and Keddie, 1996). Juvenile
P. americana produce significantly more methane than
adults, particularly when on high-fiber diets (Kane and
Breznak, 1991), and demonstrable differences occur in
the proportions of VFAs in the guts of adults versus juvenile
stages (Blaberus discoidalis) fed on the same dog food
diet (McFarlane and Alli, 1985).
Coprophagy
Although coprophagy simply means feeding on fecal material,
it is an extremely complex, multifactorial behavior
(Ullrich et al., 1992; Nalepa et al., 2001a). Fecal ingestion
can be subdivided into several broadly overlapping categories,
depending on the identity of the depositor, the nature
of the fecal material, the developmental stage of the
coprophage, and the degree to which feces are a mainstay
of the diet. Many cockroaches feed on the feces of vertebrates,
such as Periplaneta spp. in sewers or caves, desert
cockroaches attracted to bovine and equine dung
(Schoenly, 1983), and a variety of species attracted to bird
droppings (Fig. 5.2). Here we highlight the feces of invertebrate
detritivores (including conspecifics) as a source of
cockroach food, and divide the behavior into three, not
mutually exclusive categories.
78 COCKROACHES