Wings And Flight

Adult cockroaches with fully developed flight organs have two sets of wings that reach or surpass the end of the abdomen, completely covering the abdominal terga. The hindwings are membranous, but the forewings (tegmina) are somewhat sclerotized. In most species the tegmina cross each other, with the left tegmen covering a portion of the right, and with the covered portion of a different texture and color. There are also cases where the fore-

wings are transparent and similar in size and texture to the hindwings (e.g., Paratemnopteryx suffuscula, Pilema cribrosa, Nocticola adebratti, Cardacus (= Cardax) wil-leyi), or hardened and elytra-like (e.g., Diploptera and other beetle mimics).

The entire wing apparatus of cockroaches shows clear adaptations for a concealed lifestyle (Brodsky, 1994). Dorsoventral flattening has altered the structure of the thoracic skeleton and musculature, and when at rest the wings are folded flat against the abdomen. One exception is Cardacopsis shelfordi, whose wings do not lie on the abdomen with the tips crossing distally, but diverge as in flies (Karny, 1924 in Roth, 1988). Elaborate mechanisms of radial and transverse folding allow the delicate hind-wings to fit under the more robust tegmina. In repose, the anal lobe of the hindwing is always tucked under the anterior part of the wing (remigium). Polyphagids accomplish this with a single fold line (Fisk and Wolda, 1979), but in other cockroaches this area is folded along radial lines into a simple fan. There may be apical rolling (e.g., Prosoplecta nigrovariegata, Pr. coccinella, Choristima spp.) or folding (e.g., Anaplecta) of the remigium. In some species (e.g., D. punctata), this crease is in the middle of the wing, allowing for a folded wing with only half the length and a quarter of the area of the unfolded wing (Fig. 2.9). These more elaborate strategies of wingfolding are common in beetle mimics, as it allows for the protection of hindwings that exceed the length of the tegmina (Shelford, 1912a; Roth, 1994). Patterns of wingfolding, together with other wing characters, can be useful in cockroach classification (Rehn, 1951; Haas and Wootton, 1996; Haas and Kukalova-Peck, 2001). A number of generic names originate from wing characters, for example, Plecoptera (Gr., plaited + wing), Chorisoneura (Gr., separate + veins), Symploce (Gr., woven together), Isch-noptera (Gr., slender + wing) (Blatchley, 1920).

Cockroaches are "hindmotor" flyers. The hindwing is

Fig. 2.9 Wing folding in Diploptera punctata; (A) dorsal view, right tegmen and wing expanded, longitudinal and transverse folds marked as dotted lines; from Tillyard (1926). (B) Pos-terodorsal view of a wing in the process of folding. Drawing by Robin Wootton, courtesy of Robin Wootton and Fabian Haas.

Fig. 2.9 Wing folding in Diploptera punctata; (A) dorsal view, right tegmen and wing expanded, longitudinal and transverse folds marked as dotted lines; from Tillyard (1926). (B) Pos-terodorsal view of a wing in the process of folding. Drawing by Robin Wootton, courtesy of Robin Wootton and Fabian Haas.

17 18 19 20

20 mm

Fig. 2.10 Flight in Periplaneta americana; consecutive film tracings of a single wingbeat. The forewings reach the top of the stroke just as the hindwings pass the top of the stroke and begin to pronate (#3). As a result, both pairs pronate nearly simultaneously (#4), so that the hindwings, moving faster, are ahead of the forewings (#5), approach the bottom of the stroke, supinate, and go up (#12-20). From Brodsky (1994), by permission of Oxford University Press.

the main source of propulsion (Brodsky, 1994), and the two pairs of wings operate independently and slightly out of phase (Fig. 2.10). In basal cockroaches the tegmina seem to be an integral part of the flight mechanism, but in the more derived species their direct use in flight is less common (Rehn, 1951). During flight, aerodynamically induced bending of the cerci serves as a feedback in regulating wingbeat frequency (Lieberstat and Camhi, 1988). It is generally believed that the majority of winged cockroaches are rather inept fliers and lack the ability to sustain long-distance flight (Peck and Roth, 1992). Flight ability within the group varies, of course, and even weak fliers can be quite maneuverable in the air, with various strategies for evading predators. A number of small tropical species are known to be strong fliers, capable of sustained flights in a straight line or with slight lateral curves. They are able to increase altitude but cannot hover (Farnsworth, 1972).

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