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

ton, 1980). Males are good fliers and are generally located
higher than females, most of which remain on or near the
ground. Females seldom fly and, except for Parc. pennsylvanica,
all have reduced wings. The inability to fly, however,
is not always correlated with low perch height. Both
nymphs and brachypterous females of Ectobius sylvestris
walk on trunks into tree canopies (Vidlička, 1993).
Cockroaches appear to sort themselves in the vertical
dimension via their differential sensitivity to zones of temperature,
humidity, and wind currents (Edney et al., 1978;
Appel et al., 1983). Schal (1982) found significant differences
in these variables up to a height of 2 m in the tropical
forest subcanopy. In one experiment, individually
marked E. involucris were blinded, then placed at heights
where they usually do not occur; all individuals migrated
back to their typical perch zone. This stratification along
micrometeorological gradients relates to the ascent of
warm air and pheromone dispersion at night. Females
emit sex pheromones while perching, and temperature
inversions carry the pheromones aloft. Males perching
higher than females would be able to detect rising pheromones
and locate receptive females. Perching behavior in
adults, then, is primarily a mate-finding strategy (Schal,
1982; Schal and Bell, 1986), a conclusion supported by the
observations of Gorton (1980). Among the temperate
species he studied in Kansas, males were generally found
high, females low, and copulating pairs in between. Vertical
stratification may also be related to communication
between males and females in desert cockroaches (Hawke
and Farley, 1973), but data are lacking to support this idea
or to exclude other explanations.
SEASONAL ACTIVITY
Although many cockroach species live in relatively stable
environments like tropical caves and lowland rainforests,
others contend with the annual rhythmicity of seasonal
climates. These include the warm-cold cycles of temperate
zones and high mountains, and the alteration of wet
and dry seasons in various tropical habitats. Cockroaches
cope with environmental extremes and fluctuating availability
of food in these environs by using varying combinations
of movement, habitat choice, physiological
mechanisms, and lifecycle strategies. Cockroaches may
track food sources, such as those species that move into
the canopy or beneath particular trees coincident with
new leaf production or the appearance of spent flowers or
rotten fruit. In Puerto Rico, for example, branch bagging
indicated that cockroaches were more abundant on
Manilkara spp. during the wet season, but on Sloanea
berteriana during the dry season (Schowalter and Ganio,
2003). Cockroaches in seasonal environments may move
into more benign microhabitats during harsh climatic
conditions, like burrowing into deeper soil horizons or
litter piles. In summer when their open woodlands habitat
is excessively dry, Ischnoptera deropeltiformis can be
found clustered in the damp area beneath recumbent
portions of sedge-like grass clumps in creek beds (Lawson,
1967). Logs lying on the soil surface also serve as
refugia for forest-dwelling cockroaches during dry periods
(Lloyd, 1963; Horn and Hanula, 2002). Because of
surface contact with the soil and the concomitant higher
level of fungal invasion, recumbent logs maintain a
higher moisture content than standing wood or the top
layers of the forest floor (van Lear, 1996). Log refugia may
be particularly important in deciduous forests, where 50–
70% of incident radiation penetrates to the forest floor
when trees are in their leafless state, as compared to less
than 10% when leaves are fully expanded (Archibold,
1995). Likewise, the spaces beneath stones and logs as well
as similarly buffered microhabitats may be seasonally occupied.
In the high alpine zone of New Zealand, individuals
of Cel. quinquemaculata burrow deep among buried
rock fragments in winter, but in summer are found under
surface rocks (Sinclair et al., 2001). In the United Kingdom
and most of Western Europe, Blatta orientalis can
survive normal winters outdoors provided it can avoid
short-term extremes of temperature by choosing suitable
harborage such as sewers, culverts, and loose soil (le
Patourel, 1993). Roth (1995b) noted that cavernicolous
Nocticola brooksi leave the more open caves of western
Australia as these lose moisture during the dry season.
Using light trap collections in Panama, Wolda and Fisk
(1981) demonstrated that cockroaches may show cyclic
activity even in habitats lacking obvious climatic cycles.
In both a seasonal and an aseasonal site, adults were most
common between April and July, corresponding to the
rainy season in the seasonal site. In follow-up experiments,
Wolda and Wright (1992) regularly watered two
plots throughout the dry season on Barro Colorado Island
in Panama for 3 yr, with two unwatered plots as
controls. Windowpane traps were used to monitor cockroaches
and other insects. Forty-six cockroach species
were captured, with tremendous variation in numbers
between years. Seasonal variation was also common but
could not be attributed to the experimental treatment.
The author concluded that rainfall was not the proximate
cause of cockroach seasonal activity. Staggered seasonal
peaks suggested strong interactions among some congeneric
species (Fig. 3.5) (Wolda and Fisk, 1981).
Withstanding Cold
Cockroaches, like other invertebrates, have a diversity of
responses to cold temperatures (Block, 1991). Each strategy
entails energetic costs, with many interacting factors,
42 COCKROACHES