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

them (Prokopy and Roitberg, 2001). Behavioral observations,
distance measures, and association patterns in the
field are all appropriate (Whitehead, 1999), but an explicit
description of the criteria used in arriving at a social
description is the logical first step.
Aggregations:Two Subdivisions
We divide cockroach aggregations into two categories, on
the basis of the mechanism by which they are formed: cohort
aggregations and affiliative aggregations. Cohort
groups are formed by the non-dispersal of neonates after
the hatch of an ootheca, and represent kin groups.
Whether a cohesive sib group results in a cohort aggregation
or is incorporated into an affiliative aggregation depends
on the oviposition behavior of the female. The
placement of an ootheca in an area remote from conspecifics
by an oviparous female, or oviposition by a solitary
ovoviviparous female will result in a group comprised
solely of siblings. There are currently few reports
of this kind of aggregation. In Lanxoblatta emarginata,
group size is the mean brood size or slightly less, suggesting
that in this case, aggregation of nymphs results from
non-dispersal of a sib group (Grandcolas, 1993a).We suspect
that some species of forest cockroaches whose
nymphs live in the leaf litter form cohort aggregations.
Affiliative aggregations are multigenerational groups that
may include all developmental stages and both sexes.
They are fluid societies formed by both the incorporation
of cohorts of nymphs hatched into the group and by
immigration. No genetic relationships are implied for
affiliative aggregations, but they are not ruled out. Cockroaches
that are urban pests form affiliative aggregations,
and, along with cave cockroaches, are the best characterized
in terms of gregarious behavior.
Relatedness within Groups
A key issue to address in the analysis of any social behavior
is the degree of relatedness of group members; in
cockroaches the variation is considerable. At one end of
the spectrum, cockroach aggregations are not always
species specific (Table 8.1). No overt agonistic encounters
are observed in mixed-species groups, but, given the
choice, individuals will usually associate with conspecifics
(Brossut, 1975; Rust and Appel, 1985). Blatta orientalis
and B. germanica mixed in the laboratory soon form segregated
groups (Ledoux, 1945). Initially separated taxa,
however, may eventually mingle if their habitat requirements
coincide. Everaerts et al. (1997) placed two closely
related Oxyhaloinae species, Nauphoeta cinerea and Rhyparobia
maderae, together in laboratory culture. At first
they stayed in monospecific groups, but the degree of
mixing increased with time, and the taxa were randomly
distributed by the fifth day. While intraspecific grouping
in cockroaches should be considered the general rule,
conditions of high density or scarcity of resources, such
as suitable harborage or pockets of high humidity, may
result in mixed groups. Mixed-species social groups also
are reported from birds, hoofed mammals, primates, and
fish, and these typically display gregarious behavior similar
to that seen in single-species groups (Morse, 1980).
Although there are no available data on the relatedness
of individuals in natural aggregations, populations of B.
germanica within a building are more closely related than
populations between buildings (C. Rivault, pers. comm.
to CAN). There are also indications that aggregations are
cohesive relative to other groups of the same species. In
B. germanica almost no mixing of aggregations occurs,
even if several are in close proximity (Metzger, 1995);
mark-recapture studies show that only 15% of the animals
left their initial site of capture (Rivault, 1990). In the
cave cockroach Eublaberus distanti, 90% of individuals
remained in the same group during a 30-day period (R.
Brossut in Schal et al., 1984). Site constancy is also known
in P. americana (Deleporte, 1976; Coler et al., 1987). It is
Table 8.1. Examples of mixed-species aggregations in
cockroaches. Additional examples are given in Roth
and Willis (1960).
Species Harborage Reference
Periplaneta americana, In stumps, under Dozier (1920)
Eurycotis floridana bark, in corded
wood
P. americana, Blatta In cupboard of Adair (1923)
orientalis, Blattella home
germanica
Schizopilia fissicollis, Under bark Grandcolas (1993a)
Lanxoblatta
emarginata
Schultesia In bird’s nest Roth (1973a)
lampyridiformis,
Chorisoneura sp.,
Dendroblatta
onephia
B. germanica, In cracked tele- Appel and Tucker
P. fuliginosa, phone pole (1986)
P. americana
Aglaopteryx diaphana, In bromeliads, Hebard (1917)
Nyctibora laevigata, Jamaica
Cariblatta insularis
Variety of combinations: In sewers Eads et al. (1954,
Blatta orientalis,
pers. comm. to
P. americana, LMR)
P. fuliginosa,
Parcoblatta spp.
SOCIAL BEHAVIOR 133