Trophic stages of protozoans are vulnerable when they are passed from adult to offspring during proctodeal trophallaxis in the wood-feeding cockroach Cryptocercus. Some flagellate species are extremely large—Barbu-lanympha may be up to 340 ^ long (Cleveland et al., 1934),and first instars of Cryptocercus are unusually small (Nalepa, 1996). Consequently, large flagellates may not be able to pass through the proventriculus of early instars without being destroyed; the phenomenon has been reported in termites. Remnants of the flagellate Joenia were observed in the gizzards of all young Kalotermes examined by Grasse and Noirot (1945). It may take several molting cycles before the gizzard of the young host is of a diameter to allow passage of the largest flagellates. Typically, the large protozoans are the last ones established in Cryptocercus; they are not habitually found in the hindgut until the third instar (Nalepa, 1990). Until then, the numerous flagellates passed from adult to offspring in the proctodeal fluids are a high-quality, proteinaceous food (Grasse, 1952) available at low metabolic cost to the consumer (Swift et al., 1979). The normal death of protozoans within the gut may also contribute to microbial protein in the hindgut fluids. Cleveland (1925) indicated that "countless millions of them must die daily" in a single host.
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