Ecological Correlates of Flight Condition

A number of papers have focused on the ecological determinants that may select for wing retention versus loss in various insect groups. Chopard (1925) was the first to examine the phenomenon in cockroaches, and divided cockroach genera into one of three wing categories: (1) tegmina and hindwings developed in both sexes; (2) wings short or absent in females only; and (3) wings short or absent in both sexes. He then arranged genera by collection locality and concluded that flightlessness was correlated with certain geographic locations. Rehn (1932b), however, demonstrated that each of the three listed conditions can be displayed by different species within the same genus, and refuted the idea that flightlessness was correlated with geography. Rehn could find no single factor that selected for wing reduction in the cockroaches he studied (New World continental and West Indian species), but thought that "altitude and possibly humidity or aridity under special conditions" might be involved. More recently, Roff (1990, Table 1) surveyed the literature and concluded that cockroaches as well as other insects that live in deserts, caves, and social insect nests have a higher than average incidence of flightlessness. He also found that a lack of flight ability was not exceptionally high on islands, in contrast to conventional thought.

Generalizations on the correlation between flight ability and habitat are difficult to make for cockroaches. With few exceptions, conclusions are based on wing length, and habitat type is inferred from daytime resting sites or baited traps. As discussed above, the possession of full-sized wings is not always a reliable index of flight ability, and the location of diurnal shelter is only a partial indication of cockroach habitat use. Although it is safe to assume that cockroaches attracted to light traps have some degree of flight ability, the traps collect only night-active species that are attracted to light, and the ecological associations of these remain a mystery. Males of Neolaxta, for example, are very rarely seen in the field, but can be collected in considerable numbers from light traps (Mon-teith, in Roth, 1987a). Given those caveats (there will be more later), we will here examine wing trends in some specific habitat categories.

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