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

Fig. 5.11 Diagrammatic sagittal section of a cockroach abdomen,
showing gland types I–IV and location of the secretory
field for gland type V. One of the two type I glands has been
omitted and its position indicated by an arrow. Only half of the
medially opening Type III gland is shown. From Roth and Alsop
(1978), after Alsop (1970), with permission from David W.
Alsop.
dibular glands of Eub. distanti, for example, is a blend of
14 products (Brossut, 1979). Brossut and Sreng (1985) list
93 chemicals from cockroach glands, some of which are
known to be fungistatic in other systems, for example,
phenols (Dillon and Charnley, 1986, 1995), naphthol,
p-cresol, quinones (Brossut, 1983), and hexanoic acid
(Rosengaus et al., 2004). Phenols have been identified
from both the sternal secretions and the feces of P. americana,
and neither feces nor the filter paper lining the
floor of rearing chambers exhibit significant fungal
growth (Takahashi and Kitamura, 1972). Other cockroaches
also produce a strong phenolic odor when handled
(Roth and Alsop, 1978). It is of interest, then, that
phenols in the fecal pellets and gut fluids of locusts originate
from gut bacteria, and are selectively bacteriocidal
(Dillon and Charnley, 1986, 1995). Given the extraordinarily
complex nutritional dynamics between cockroaches
and microbes in the gut and on feces, these kinds
of probiotic interactions are probably mandatory. It is a
safe assumption that cockroaches engage in biochemical
warfare with microbes, but they have to do so judiciously.
Blattaria have both behavioral and immunological
mechanisms for countering pathogens that successfully
breach the cuticular or gut barrier. Wounds heal quickly
(Bell, 1990), and cockroaches are known to use behavioral
fever to support an immune system challenged by
disease. When Gromphadorhina portentosa was injected
with bacteria or bacterial endotoxin and placed in a thermal
gradient, the cockroaches preferred temperatures
significantly higher than control cockroaches (Bronstein
and Conner, 1984). The immune system of cockroaches
differs from that of shorter-lived, holometabolous insects,
and mimics all characteristics of vertebrate immunity,
including both humoral and cell-mediated responses
(Duwel-Eby et al., 1991). Blaberus giganteus
synthesizes novel proteins when challenged with fungi
(Bidochka et al., 1997), and when American cockroaches
are injected with dead Pseudomonas aeruginosa, they respond
in two phases. Initially there is a short-term, nonspecific
phase, which is superseded by a relatively longterm,
specific response (Faulhaber and Karp, 1992).
When challenged with E. coli, P. americana makes broadspectrum
antibacterial peptides. Activity is highest 72–96
hr after treatment, and newly emerged males respond
best (Zhang et al., 1990). Cellular immune responses are
mediated by hemocytes, primarily granulocytes and plasmatocytes
(Chiang et al., 1988; Han and Gupta, 1988)
whose numbers increase in response to invasion and
counter it using phagocytosis and encapsulation (Verrett
et al., 1987; Kulshrestha and Pathak, 1997).
Sexual contact carries with it the risk of sexually transmitted
diseases (e.g., Thrall et al., 1997), but no cockroaches
were listed in an extensive literature survey on the
topic (Lockhart et al., 1996). Wolbachia, a group of cytoplasmically
inherited bacteria that are widespread among
insects (including termites—Bandi et al., 1997) have not
yet been detected in cockroaches, but few species have
been studied to date (Werren, 1995; Jeyaprakash and Hoy,
2000). Further surveys of Blattaria may yet detect Wolbachia,
but because they are transmitted through the
cytoplasm of eggs, these rickettsiae may have trouble
competing with transovariolly transmitted bacteroids
(Nathan Lo, pers. comm. to CAN).
The cost of battling pathogens likely has life history
consequences for cockroaches, since it does in many animals
that inhabit more salubrious environments (Zuk and
Stoehr, 2002). Immune systems can be costly in that they
use energy and resources that otherwise may be invested
into growth, reproduction, or maintenance, thus making
them subject to trade-offs against other fitness components
(Moret and Schmidt-Hempel, 2000; Møller et al.,
2001; Zuk and Stoehr, 2002). It may be possible, for example,
that the prolonged periods of development typical
of many cockroaches may be at least partially correlated
with an increased investment in immune function. The
life of a cockroach has to be a fine-tuned balancing act between
exploiting, cultivating, and transmitting microbes,
while at the same time suppressing, killing, or avoiding the
siege of harmful members of the microbial consortia that
surround them. Until recently, these relationships have
been difficult to study because the microbes of interest are
poorly defined, many have labile or nondescript external
morphology, and most cannot be cultured in vitro. The
availability of new methodology that allows insight into
the origins, nature, and functioning of microbes (Moran,
2002) in, on, and around cockroaches portends a bright
future for studies on the subject. Until then, it should be
considered that the ability of cockroaches to live in just
about any organic environment may have its basis in their
successful management of the varied, sophisticated, cooperative,
and adversarial relationships with “inconspicuous
associates” (Moran, 2002).
88 COCKROACHES