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

Table 8.2. Aggregation of cockroach nymphs on filter paper conditioned with the feces of other
cockroach species. Six to eight trials were performed with each combination using 20 nymphs per
run. Plus-signs represent significant aggregation to conditioned paper as compared to controls.
From Bell et al. (1972).
Species conditioning papers
Nymph species P. am. B.o. P.p. E.p. B.d. B.f.
After 20 min
P. americana
Blatta orientalis
Parc. pennsylvanica
Eub. posticus
Blab. discoidalis
Byr. fumigata
After 12 hr
P. americana
Blatta orientalis
Parc. pennsylvanica
Eub. posticus
Blab. discoidalis
Byr. fumigata
range attractants (Ishii and Kuwahara, 1967; Bell et al.,
1972; Roth and Cohen, 1973), then as arrestants (Burk
and Bell, 1973). Nymphs halt their forward progress
when they encounter a filter paper contaminated with feces;
the response, however, is not strictly species specific
(Bell et al., 1972; Roth and Cohen, 1973). Cockroaches
prefer substrates contaminated by feces of their own
species, but will aggregate on surfaces contaminated by
distant relatives (Table 8.2). Periplaneta americana was attracted
to paper contaminated by all species tested, and
after 12 hr, Parcoblatta pennsylvanica was attracted to
none, not even their own. Locomotor inhibition is enhanced
by social interaction between assembled individuals;
a nymph is more likely to stop on feces-contaminated
filter paper if one or more nymphs are already in
residence. Young nymphs are most responsive to the
chemical cues, adults are intermediate, and middle instars
the least (Bret and Ross, 1985; Runstrom and Bennett,
1990). Experience matters; nymphs that hatch in an aggregation
are more likely to aggregate (Dambach et al.,
1995).
The evidence suggests that the fecal substances that
elicit aggregation behavior in cockroaches, then, are not
pheromones in the classic sense, but a functional category
of behavior-eliciting chemicals (Brossut, 1975).
Their origin is unclear, they are poorly defined, and they
lack specificity. Pheromones are, however, clearly implicated
in two species, Blab. craniifer and Eub. distanti,
where the origin of the intraspecific attractant has been
traced to the mandibular glands (Brossut et al., 1974;
Brossut, 1979). In these cockroaches the pheromone is
secreted by all individuals at all times except during the
molting period. The insects are unattractive from 72 hr
before to 24 hr after ecdysis (Brossut et al., 1974; Brossut,
1975). This inactive period occurs because the mandibular
gland is lined with cuticle (Noirot and Quennedy,
1974), which is shed along with the rest of the exoskeleton
during molt.
Proximate Mechanisms:
How Do They Aggregate?
If specific pheromones are not involved in many species,
how do groups form? Aggregation in cockroaches is generally
mediated by visual, acoustic, tactile, and/or olfactory
stimuli (Grassé, 1951). The complication is that these
often are not the only causes. Environmental factors, including
light (Gunn, 1940), temperature (Gunn, 1935),
and air movement (Cornwell, 1968) also play an important
role. Humidity is a factor, although the degree to
which it exerts an influence may be species specific (Roth
and Willis, 1960). In some cockroaches, the lower the
humidity, the stronger the tendency to aggregate (Sommer,
1974; Dambach and Goehlen, 1999). Response to
these, as well as other environmental stimuli, results in
the initial selection of a harborage, which is consequently
136 COCKROACHES