Circadian Activity

Many species exhibit daily and seasonal movements in response to their dietary, reproductive, and microenviron-mental needs; these vary with the individual, sex, developmental stage, species, day, season, and habitat. Activity patterns are expected to differ, for instance, between those cockroaches that forage, find mates, reproduce, and take refuge all in the same habitat (in logs, under bark, in leaf litter) and those that move daily between their harborage and the habitats in which they conduct most other life activities. The most common circadian activity pattern among the latter is for nymphs and adults to rest in harborages during the day, then become active as the sun sets. At dusk, adults climb or fly to above-ground perching sites (Schal and Bell, 1986), while nymphs confine their activities to the leaf litter. Some species are evidently active for short periods just after sunset, whereas others may be observed throughout the night. Within 60 min after sunset, adult males and small nymphs of Periplaneta fuliginosa emerge from their harborage, followed by medium and large nymphs and adult females. After feeding, males climb vertical surfaces, while nymphs and most females return to shelter (Appel and Rust, 1986). Males also become active earlier than females in Ectobius lap-ponicus. They begin moving in the late afternoon, while females and nymphs wait until after sunset (Dreisig, 1971). In Nesomylacris sp., most females do not become active until just before dawn, while males are active throughout the night. Females of Epilampra involucris are active at both dusk and dawn (Fig. 3.2). With few exceptions, temporal overlap among nocturnally active species is large.

Fig. 3.2 Orcadian activity of three nocturnal and one diurnal cockroach species in Costa Rican rainforest. Solid bars are a measure of conspicuousness in the field; open bars indicate locomotor activity in an outdoor insectary. Modified from Schal and Bell (1986).

Not all cockroach individuals are mobile on a nightly basis. Kaplin (1996) found that 40% of individuals of the desert cockroach Anisogamia tamerlana are active in a single summer night. In females, locomotor patterns are often associated with the reproductive cycle. In Blattella germanica, activity increases when females are sexually receptive and peaks during ovarian development. Locomotion decreases when she is forming or carrying an ootheca (Lee and Wu, 1994; Tsai and Lee, 2000). Nau-phoeta cinerea females likewise stop locomotor activity shortly after mating; activity rhythms begin again after partition (Meller and Greven, 1996b). In Rhyparobia maderae daily activity gradually decreases in parallel with the progressive development of eggs until the level characteristic of pregnancy is reached (Engelmann and Rau, 1965; Leuthold, 1966). This inactivity is correlated with a decreased requirement for locating food and mates; females rarely forage during gestation. An increase in movement prior to partition is associated with locating a suitable nursery for forthcoming neonates. In juvenile cockroaches activity is correlated with the developmental cycle. Blattella germanica nymphs are active during the first half of a nymphal stadium. During the last third of the stadium, they remain in the harborage and move very little (Demark and Bennett, 1994). Cockroaches may also "stay home" during adverse weather. The activity of E. lapponicus is inhibited by wind (Dreisig, 1971), and Lam-problatta albipalpus individuals return to harborage when disturbed by heavy rain (Gautier and Deleporte, 1986).

The distance traveled between shelter and sites of foraging and other activity varies from 28 m in field populations of Periplaneta americana (Seelinger, 1984) to no more than a meter or two in female Macropanesthia rhinoceros (D. Rugg, pers. comm. to CAN) and Lam. albipalpus (Gautier and Deleporte, 1986).

There are a number of day-active cockroach species, but little is known of their biology. Some, such as Eu-phyllodromia angustata (Fig. 3.3), live in tropical rainforest. Others inhabit more arid landscapes; these include

Fig. 3.3 The diurnal species Euphyllodromia angustata perching on a leaf, Costa Rica. Note the dead edges of leaf holes and the presence of epiphylls on the leaf surface, both of which are included in the diet of many tropical cockroaches. Photo courtesy of Piotr Naskrecki.

brightly colored Australian species in the blattellid genus Ellipsidion, and members of the blattid subfamily Poly-zosteriinae (Tepper, 1893; Mackerras, 1965a; Rentz, 1996). In Platyzosteria alternans, nymphs are diurnal while adults are nocturnal (Roach and Rentz, 1998).

Activity rhythms in cockroaches are controlled by a circadian master clock in a region of the brain anatomically and functionally connected to the optic system. Light entrains the rhythm and allows for synchronization with environmental light-dark cycles (Foerster, 2004). An absence of cockroach activity rhythms has been observed in deep tropical caves, for example, Eublaberus posticus in Trinidad (Darlington, 1970), Gyna maculipennis (probably Apotrogia n. sp.) in Gabon (Gautier, 1980), but no study has demonstrated free-running activity. Blaberus colloseus, Blab. atropos, and P. americana positioned close to cave entrances become active when the light intensity falls below 0.7 Lux (Gautier, 1974a; Deleporte, 1976). Adult and older nymphs emerge from their shelters, and younger nymphs crawl onto the surface of the cave floor at nightfall. An intensity change of 1 Lux influences activity rhythms of Blaberus craniifer in the laboratory (Wobus, 1966). Observations of cave-dwelling cockroaches in Trinidad suggest that activity rhythms also may be cued by micrometerological events like wind disturbances or an increase in temperature at the beginning of bat activity. Darlington (1968) recorded a 2.5°C increase in temperature in the evening when bats become active in the deep part of Tamana Cave. In the laboratory, Roberts (1960) found that a thermoperiod with varia tions of 5°C was sufficient to set the rhythm of R. maderae in continuous darkness.

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