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

lated congener B. signata, however, is apparently solitary
(Tsai and Lee, 2001). Sixth, laboratory data can conflict
with field descriptions. One example: studies on Schultesia
lampyridiformis reared for 20 yr in the laboratory suggest
that females use aggression to disperse nymphs after
hatch (Van Baaren and Deleporte, 2001; Van Baaren et al.,
2003). In the field (Brazil), however, Roth (1973a) found
adults and nymphs living together in birds’ nests. One
nest contained 4 males, 8 females, and 29 nymphs, and
other cockroach species were also present. Lastly, the division
of species into group living and solitary categories
is largely artificial in any case because most animal species
are in an intermediate category, found in association with
conspecifics at certain times of their lives, but not others
(Krause and Ruxton, 2002).
These issues, and others, have bearing on phylogenetically
based comparative analyses of cockroach social behavior.
While these can be powerful tools for generating
and testing ideas about the links between behavior and
ecology, attempts to map social characteristics onto
cladograms of cockroach taxa are premature. We are still
early in the descriptive phase of cockroach social behavior,
and unresolved phylogenies in many cases preclude
meaningful comparative study. Some general trends are
detectable and will be discussed below.
SOLITARY COCKROACHES
Currently, few cockroach species are convincingly classified
as solitary, that is, leading separate lives except for a
brief period of mating. One category of loners may be
those cockroaches adapted to deep caves. Although they
may cluster around food sources, troglobites are typically
solitary animals, have wide home ranges, and meet only
for mating (Langecker, 2000). The blattellid Phyllodromica
maculata is considered solitary, as juveniles do not
aggregate, nor are they attracted to filter paper contaminated
by conspecifics (Gaim and Seelinger, 1984). Paratemnopteryx
couloniana was called “relatively solitary”
by Gorton (1979), but without statement of criteria.
Thanatophyllum akinetum was described as solitary by
Grandcolas (1993a). The insects spend much of their
time motionless and flattened against dead leaves on the
forest floor in French Guiana. Laboratory tests support
the observation that individuals actively distance themselves
from conspecifics (Van Baaren and Deleporte,
2001). A solitary, cryptic lifestyle is thought to allow them
to escape detection by army ants (Grandcolas, 1998).
Nonetheless, the female broods offspring for several
hours following hatch, which is a subsocial interaction,
albeit short term, between a mother and her offspring.
Lamproblatta albipalpus was described as solitary by Gautier
et al. (1988), but considered “weakly gregarious” by
Gautier and Deleporte (1986). Males and females of this
species are found together in resting sites, but their bodies
are not in direct contact. Even strongly gregarious
cockroaches, however, can be separated in space within a
shelter under certain environmental conditions, for example,
high relative humidity (Dambach and Goehlen,
1999).
AGGREGATIONS: WHAT CRITERIA?
A variety of nonexclusive criteria have been used to delineate
cockroach aggregation behavior. These include
their arrangement in space (are they in physical contact?),
mechanisms that induce grouping (is a pheromone involved?),
and the outcome of physical proximity (do
group effects occur?). Aggregations have been described
as mandatory, nonobligatory, strong, weak, and loose,
without further detail. To most entomologists, mutual
attraction is considered the primary criterion of aggregation
behavior (Grassé, 1951; Sommer, 1974); group
membership involves more than co-location, with individuals
behaving in ways that maintain proximity to
other group members. In practice, the distinction is not
easily made, because in most cases both environmental
and social influences play a role (Chopard, 1938). Many
cockroaches predictably seek dark, humid, enclosed
spaces as shelter, and live in close association with nutritional
resources. The functional basis of a nonrandom
distribution is especially vague for the vast majority of
cockroaches regarded as crevice fauna: those found in
small groups in small shelters, for example, under logs, in
leaves, under stones, under loose bark. Eickwort (1981)
suggested testing aggregation behavior by supplementing
the resources of a group to see if it results in dispersion of
the insects. Tsuji and Mizuno (1973) and Mizuno and
Tsuji (1974) gave Periplaneta americana, P. fuliginosa, P.
japonica, and B. germanica excess harborage and found
that while adults and older nymphs shelter individually,
young nymphs seek conspecifics. The results are difficult
to interpret, because all these test species are commonly
found in multigenerational aggregations.
What, then, are necessary and sufficient criteria for
calling a cockroach gregarious? Are two nymphs found
together considered a group? Do they have to be the same
species? Are neonates that remain near a hatched ootheca
for an hour before dispersing gregarious? What if they remain
for 3 days? Do aggregation pheromones have to be
involved? Do the insects have to be touching? The literature
provides no easy answers. A broad range of variables
influences the degree to which individuals are positive,
neutral, or negative with regard to joining a group. These
include genetics, physiology, informational state, geographic
region, and the experimental protocol used to test
132 COCKROACHES