Microbes In And On Foodstuffs

Because of the intimate association of microbial consortia and the substrate they are decomposing, both are ingested by detritivores. It is the microbial material, rather than the substrate that may serve as the primary source of nutrients (Berrie, 1975; Plante et al., 1990; Anduaga and Halffter, 1993; Gray and Boucot, 1993; Scheu and Setala, 2002). Scanning electron micrographs show that millipedes, for example, strip bacteria from the surface of ingested leaf litter (Bignell, 1989), and similar to cockroaches, they can be found feeding on corpses in advanced stages of decay (Hoffman and Payne, 1969). Most foods known to be included in the diet of cockroaches in natural habitats are profusely covered with microbes. Bacteria and fungi are present on leaves before they are abscised, and their numbers increase rapidly as soon as the litter has been wetted on the ground (Archibold, 1995). The floor of a tropical rainforest is saturated with microbial decomposers, and as decay is successional, different species of microbe are associated with different parts of the process. A square meter of a tropical forest floor may contain leaves from 50 or more plant species, and each leaf type may have a different microflora and microfauna. Microbial populations may also vary with season, with climate, with soil, and with the structure of the forest; there is no simple way to recognize all of the variables (Stout, 1974). Dead logs, treeholes, bird and rodent nests, bat caves, and other such cockroach habitats are also microbial incubators. Bacteria are ubiquitous, but flagellates, small amoebae, and ciliates are also important agents of decomposition, and are associated with every stage of plant growth and decline, from the phyllo-plane to rhizosphere (Stout, 1974). Fermenting fruits and plant exudates (e.g., oozing sap) support the growth of yeasts, which are exploited as a source of nutrients in many insect species (Kukor and Martin, 1986). Cockroaches in culture favor overripe fruit, with the rotted part of the fruit eaten first, and fruit fragments intercepted by leaves in tropical forests are far from fresh. Blattella vaga has been observed in large numbers around decaying dates on the ground (Roth, 1985). Vertebrate feces are obviously rich sources of microbial biomass, particularly in bat caves, and, as discussed in Chapter 4, some cave cockroaches apparently assimilate bacteria from ingested soil.

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