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

gether freely in the laboratory (e.g., Panesthia cribrata—
O’Neill et al., 1987), but this is quite different from a solitary
insect attempting to join an established group under
natural conditions. When two isolated young nymphs of
P. americana are placed in contact with each other, they
undergo a “ritual of accommodation” which may become
aggressive (Wharton et al., 1968). Behaviors include
“sampling” each other’s deposited saliva with palpi or antennae,
stilting, tilting their bodies, bending their abdomens,
antennal fencing, leg strikes, and biting. The decision
to accept new members into the aggregation can be
important when changing ecological conditions (e.g.,
food availability) alter the relationship between group
size and fitness (Giraldeau and Caraco, 1993).
Choosing Shelter
Cockroaches use a variety of criteria in selecting harborage
sites. In general, cockroaches orient to sheltered sites
near food and water, and will remain true to a site as long
as both are adequate (Ross et al., unpubl., in Bret et al.,
1983; Rivault, 1990). Both the texture (Berthold, 1967)
and orientation of surfaces (Bell et al., 1972) and the size
of the harborage (Berthold and Wilson, 1967; Mizuno
and Tsuji, 1974) are influential. Groups of cockroaches
may segregate by body size, depending on the height of
available space (reviewed by Roth and Willis, 1960). Small
nymphs in the absence of older conspecifics prefer narrower
crevices than do adults; however, they prefer larger
harborages if other cockroaches are present, indicating
that social stimuli supersede harborage height preferences
(Tsuji and Mizuno, 1973; Koehler et al., 1994). Aggregation
behavior of young nymphs is more pronounced
in open areas than in shelters, suggesting that
they may satisfy their thigmotactic tendencies with each
other when the physical environment is devoid of tactile
stimuli (Ledoux, 1945).
Pheromones
Pheromones rule the social world of cockroaches. The
chemical repertoire includes both contact pheromones
and volatiles, and these function as sex pheromones, attractants,
arrestants, dispersants, alarm pheromones, trail
pheromones, and mediators of kin recognition. Chemical
stimuli help orchestrate cockroach aggregation behavior,
and have been studied primarily for their potential
in pest management.
Oviposition Pheromones
The location of first instars within their habitat is largely
determined by the oviposition behavior of females, who
tend to deposit their eggs near resources. Female Periplaneta
brunnea, for example, generally glue their oothecae
near a food supply (at least they do in 1 gal battery
jars) (Edmunds, 1957). There is some evidence to suggest,
however, that, like locusts (Lauga and Hatté, 1977; Loher,
1990), some cockroaches may employ oviposition pheromones.
These serve to either convene gravid females in
certain locations for egg laying, or attract them to sites
where conspecifics have previously deposited oothecae.
Edmunds (1952) found 184 oothecae of Parcoblatta sp.
deposited in close proximity under tree bark. Similarly,
oothecae of Supella longipalpa were found in clusters by
Benson and Huber (1989). The authors observed ovipositing
females deposit a drop of “genital fluid” on
oothecae, and suggested that it contains a pheromone
that attracts other females. Gravid females of B. germanica
generally do not leave the harborage (Cochran,
1983b); consequently, first instars hatch into an aggregation
(Rivault, 1989; Koehler et al., 1994). Stray females,
however, may actively seek aggregations for oviposition.
Escaped females of B. germanica in laboratory colonies
laid their oothecae near a group of conspecific nymphs
(Ledoux, 1945).
Aggregation Pheromones?
Enormous effort has been dedicated to localizing and
characterizing the aggregation pheromone of pest cockroaches.
The results, however, are still equivocal. Ledoux
(1945) first proposed that aggregation in cockroaches was
the result of mutual attraction of a chemical nature, and
Ishii and Kuwahara (1967, 1968) identified fecal material
as the source of the cue. Riding the wave of pheromone
research during the 1960s, these authors dubbed the fecal
chemical “aggregation pheromone.” They suggested that
it originates in the rectal pad cells and that it is applied to
fecal pellets as they are being excreted. Cuticular waxes
apparently absorbed the fecal pheromone also, as ether
washings of the abdomen had higher activity than ether
washings of other parts of the body. More recent work has
identified more than 150 volatile and contact chemicals
from German cockroach fecal pellets (Fuchs et al., 1985,
in Metzger, 1995; Sakuma and Fukami, 1990). The attractiveness
of individual components depends not only
on the type of extraction used, but also the biological assay
used to test them (reviewed by Dambach et al., 1995),
and the stock or population of B. germanica used as test
subjects. Mixtures of fecal compounds are generally more
effective than single components (Scherkenbeck et al.,
1999). Cuticular wax may be attractive independent of
any chemicals absorbed from excretory material. Rivault
et al. (1998) found that cuticular hydrocarbons alone,
from any part of the body, can elicit aggregation behavior.
Fecal chemicals seem to function initially as short-
SOCIAL BEHAVIOR 135