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

Fig. 1.6 Diagrammatic representation of cockroach species showing comparative size, comparison
between males (left) and females (right), degree of size variation within a sex (minimum
measurement on left, maximum measurement on right), and relationship between tegmen and
body length. From Cornwell (1968), based on data from Hebard (1917). With permission of Rentokil
Initial plc.
Parcoblatta species (Fig 1.6) (Parc. lata, Parc. bolliana,
Parc. divisa, Parc. pennsylvanica). Males of the latter are
22–30 mm in length, while females measure 13–20 mm.
In Parc. fulvescens, however, females outsize the males
(Cornwell, 1968; Horn and Hanula, 2002).
Like other animals, the pattern of sexual size dimorphism
within a cockroach species is related to the relative
influence of body size on fecundity in females and mating
success in males. In G. portentosa, males tend to be
larger than females, and big males are the more frequent
victors in male-male contests (Barth, 1968c; Clark and
Moore, 1995). In species where males offer food items to
the female as part of courtship and mating, nuptial gifts
may reduce the value of large size in females and increase
its value in males (Leimar et al., 1994; Fedorka and
Mousseau, 2002). This hypothesis is unexplored in the
cockroach species that employ such a mating strategy.
One proximate cause of female-biased sexual size dimorphism
in cockroaches is protandry. Males may mature
faster than females because it gives them a mating advantage,
but become smaller adults as a consequence. Males
of Diploptera punctata, for example, usually undergo one
fewer molt than do females, and require a shorter period
of time to mature (Willis et al., 1958). Males of Anisogamia
tamerlana mature in five instars, and females in six
(Kaplin, 1995).
Physiological correlates of body size have been examined
in some cockroaches; these include studies of metabolic
rate and the ability to withstand extremes of temperature,
desiccation, and starvation. Coelho and Moore
8 COCKROACHES