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

Bolker, 2003). The highly complex and tightly coordinated
interactions of Blattabacterium endosymbionts
with their hosts during transovarial transmission and
embryogenesis (Sacchi et al., 1988, 1996, 1998b) suggest
that these symbionts may influence the earliest stages of
cockroach development.
MICROBES AS PATHOGENS
Microbes can be formidable foes. Most animals battle infection
throughout their lives, and devote substantial resources
to responding defensively to microbial invaders
(e.g., Irving et al., 2001). Cockroaches, like other animals
that utilize rotting organic matter (Janzen, 1977), must
fend off pathogenesis and avoid or detoxify the chemical
offenses of microbes. Most Blattaria lead particularly
vulnerable lifestyles. They are relatively long-lived insects
that favor humid, microbe-saturated environments;
many live in close association with conspecifics, particularly
during the early, vulnerable part of life. They also
have a predilection for feeding on rotting material, conspecifics,
feces, and dead bodies. Pathogens and parasites
such as protozoa and helminths (e.g., Fig. 5.10) are no
doubt a strong and unrelenting selective pressure, but
cockroach defensive strategies must be delicately balanced
so that their vast array of mutualists are not placed
in the line of fire. An example of these conflicting pressures
lies in cockroach social behavior. On the one hand,
beneficial microbes promote social behavior. Transmission
of hindgut microbes requires behavioral adaptations
so that each generation acquires microflora from the previous
one, and consequently selects for association of
neonates with older conspecifics. On the other hand,
pathogenic microbes exploit cockroach social behavior,
in that their transmission occurs via inter-individual
Fig. 5.10 Hairworm parasite (Paleochordodes protus) of an
adult blattellid cockroach (in or near the genus Supella) in
Dominican amber (15–45 mya). From Poinar (1999); photo
courtesy of George Poinar Jr.
transfer. Oocysts of parasitic Gregarina, for example, are
transmitted via feces (Lopes and Alves, 2005), and the biological
control of urban pest cockroaches with pathogens
is predicated largely on their spread via inter-individual
contact in aggregations (e.g., Mohan et al. 1999;
Kaakeh et al.,1996). Roth and Willis (1957) document inter-individual
transfer of a variety of gregarines, coccids,
amoebae, and nematodes via cannibalism, coprophagy,
or proximity.
Cockroaches have a variety of behavioral and physiological
mechanisms for preventing and managing disease.
At least two cockroach species recognize foci of potential
infection and take behavioral measures to evade them.
Healthy nymphs of B. germanica are known to avoid dead
nymphs infected with the fungus Metarhizium anisopliae
(Kaakeh et al., 1996). The wood-feeding cockroach Cryptocercus
sequesters corpses and controls fungal growth in
nurseries (Chapter 9). The former behavior may function
to shield remaining members of the family from infection.
Vigilant hygienic behavior or fungistatic properties
of their excreta or secretions may also play a role throughout
the gallery system. Fungal overgrowth of tunnels is
never observed unless the galleries are abandoned (CAN,
pers. obs.).
The glandular system of cockroaches is complex and
sophisticated, with seven types of exocrine glands found
in the head alone (Brossut, 1973). The mandibular glands
of two species (Blaberus craniifer and Eublaberus distanti)
secrete an aggregation pheromone; otherwise the function
of cephalic glands is unknown (Brossut, 1970, 1979).
The secretion of some of these may have antimicrobial
properties, and could be spread over the surface of the
body to form an antibiotic “shell” during autogrooming,
particularly if the cockroach periodically runs a leg over
its head or through its mouthparts during the grooming
behavioral sequence. Autogrooming therefore may function
not only to remove potential cuticular pathogens
physically, but also to disseminate chemicals that curtail
their growth or spore germination. Dermal glands are
typically spread over the entire abdominal integument of
both males and females (200–400/mm 2 ) (Sreng, 1984),
and five types of defensive-type exocrine glands have
been described (Roth and Alsop, 1978) (Fig. 5.11). Most
of the latter produce chemical defenses effective against
an array of vertebrate and invertebrate predators (Fig.
1.11A), but the influence of these chemicals on non-visible
organisms is unexplored. They may well function as
“immediate effronteries” to predators as well as “long
term antagonists” to bacteria and fungi (Roth and Eisner,
1961; Duffy, 1976), and act subtly, by altering growth
rates, spore germination, virulence, or chemotaxis (Duffy,
1976). Most cockroach exocrine glands produce multicomponent
secretions (Roth and Alsop, 1978). The man-
MICROBES: THE UNSEEN INFLUENCE 87