In tropical rainforests leaf surfaces are "night habitat" for many crepuscular and nocturnal cockroaches. It is the only time and place that the majority of cockroaches that live in rainforests of Queensland, Australia (D. Rentz, pers. comm. to CAN), and Costa Rica (WJB, pers. obs.) can be seen. The insects emerge from harborage on the forest floor, move up the plants, then out onto foliage, or they move onto leaves from the innumerable hiding places in the different strata of the forest canopy. Adhesive footpads (arolia and euplantae) help the cockroaches negotiate sleek planes of vegetation, but it is only young leaves that commonly have smooth, simple surfaces. As leaves age they become elaborate, textured habitats rich in potential food sources (Walter and O'Dowd, 1995) (Fig. 4.4). In general, leaves provide two menu categories for cockroaches (WJB, unpubl. obs.). First, leaves act as serv-
ing trays for the intercepted rain of particulate organic matter that falls perpetually or seasonally from higher levels of the forest. This includes bird and other vertebrate feces, pollen, spores, leaves, twigs, petioles, sloughed tree bark, flower parts, and pieces of ripe fruit originating from the plant and from sloppy vertebrate eaters. Also offered on these leaf trays are dead leaf material around herbivore feeding damage, and the excreta, honeydew, silk webbing, eggshells, exuvia, and corpses of other arthropods. Live mites, aphids, and other small vulnerable arthropods on leaves are potential prey items. The second menu category on leaves in tropical forests is the salad course: leaves are gardens that support a wide range of nonvascular plants (epiphylls) and microbes. These include lichens, bryophytes, algae, liverworts, mosses, fungi, and bacteria.
Cockroaches in Costa Rican rainforest have been observed feeding on the majority of items listed above (WJB and J. Aracena, unpubl. obs.). Dissections of the cockroaches and inspection of their gut contents, however, indicate that ingestion of the different food types can be rather specific. Those cockroaches for which fairly large sample sizes are available are listed in Table 4.2. Capucina rufa and Cap. patula forage on dead logs, feeding on epi-phylls, fungi, and bark scraps. Epilampra involucris females perch near the ground, where they feed on ground litter and the materials that fall onto it. Males of this species, which perch on leaves at heights of up to 50 cm, eat algae, bryophytes, lichens, pollen, spores, fruit, and flakes of shed bark. A subset of small, mobile species fly about in the canopy and scrape epiphylls from leaf surfaces at night. Imblattella and Cariblatta feed primarily on leaf trichomes, blue-green algae, liverworts, and spores. Only algae were found in the guts of male, female and juvenile Car. imitans. Trichomes, which normally interfere with foraging by small herbivores and carnivores (Price,
2002), are ingested by several cockroach species (WJB, unpubl. obs.). The many tropical cockroaches that fulfill their nutritional requirements by feeding on the broad variety of materials offered on leaf laminae may, like ants (Davidson et al., 2003), be categorized as leaf foragers. Those that specialize on the epiphylls and other plant products (trichomes, pollen, honeydew) found in this habitat may be described as cryptic herbivores (Hunt,
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