PROTOZOA
It is probable that with few exceptions protozoa found in the digestive tract are not necessary for survival of the cockroach. However, very few experiments have been performed to determine the importance, if any, of these microorganisms to the host. Cleveland (1925) removed the protozoa from the cockroach (possibly Periplaneta americana) by oxygenation at 3.5 atmospheres. The ciliates Nyctotherus and Balantidium, flagellates Lophomonas and Polymastix, the amoeba Endamoeba blattae, and three unidentified protozoa were killed by this treatment, yet the insects lived normally after defaunation.
Armer (1944) studied the effects of high-carbohydrate, high-fat, and high-protein diets, as well as starvation, on the intestinal protozoa (Nyctotherus ovalis, Endamoeba blattae, Endolimax blattae, Lophomonas striata, and Lophomonas blattarum) in Periplaneta americana. Starvation of the host lowered the incidence or eliminated most of the protozoa, but a high-carbohydrate diet maintained them at a relatively high level. Lophomonas blattarum was eliminated by a high-protein diet, and practically eliminated by a high-fat diet. Lophomonas striata was eliminated from some hosts that were kept on high-fat and high-protein diets. Endamoeba blattae showed a decrease in infection rate when the cockroaches were maintained on high-fat and high-protein diets. The effects of diets on Endolimax blattae were not uniform.
It has been shown by Cleveland (1930, 1948) and Cleveland et al. (1931, 1934) that the wood-feeding cockroach Cryptocercus punctulatus depends upon certain intestinal protozoa for survival; these protozoa utilize as food the wood ingested by this cockroach. The wood is broken down into compounds the cockroach can utilize by the protozoa which elaborate a cellulase and possibly a cellobiase (Trager, 1932). Only molting nymphs of Cryptocercus can pass the protozoa on to the newly hatched young, so that molting and hatching must happen concurrently each year or the young die.
The sexual cycles in species of protozoa in the genera Trichonympha, Saccinobaculus, Oxymonas, Monocercomonoides, Hexamita, Eucomonympha, Leptospironympha, Urinympha, Rhynchonympha, Macrospironympha, and Barbulanympha (fig. 3, B) are induced by hormones produced by Cryptocercus only during its molting period (Cleveland, 1931, 1947, 1947a, 1949-1956a). Perhaps the prothoracic gland hormone of the host may be responsible for initiation of the flagellate sexual cycles (Cleveland and Nutting, 1955). The protozoan sexual cycles may be used as indicators of the onset of molting in Cryptocercus; thus different species of protozoa begin their sexual cycles from 35 days before to 2 days after molting of the cockroach (Cleveland and Nutting, 1954). Hollande (1952) and Grassé (1952) have reviewed the roles and the evolution of the flagellates in Cryptocercus and in termites.
The protozoa of cockroaches and termites are clues to the relationship between these two groups of insects. Kirby (1927) pointed out similarities between Endamoeba blattae of Periplaneta and the amoebae of the termite Mirotermes, suggesting that these protozoans were probably derived from an amoeba in an ancestor common to both blattid and termite. Kirby (1932, in Kidder, 1937) found a species of Nyctotherus in Amitermes that resembles Nyctotherus ovalis from domestic cockroaches. The belief that the termites and cockroaches had a common origin is also strengthened by the similarities between the hypermastigotes of both Cryptocercus and termites (Cleveland et al., 1934).
The cockroaches Cryptocercus and Panesthia both feed on wood, but the protozoa found in Panesthia resemble more closely the species in domestic cockroaches than those in Cryptocercus. The Clevelandellidae (from Panesthia) are closely related to Nyctotherus and have probably evolved from common ancestors. However, the separation of the Clevelandellidae from Nyctotherus must have taken place at a later date than the divergence of their hosts, otherwise representatives of that family would probably also be found in Periplaneta and Blatta (Kidder, 1937).
The protozoa of Cryptocercus can be transferred from one individual to another (Nutting and Cleveland, 1954). They can also be transferred to the termite Zootermopsis where they survive only until the host molts; the reverse is also true, Zootermopsis Protozoa can survive in Cryptocercus until the cockroach molts (Nutting and Cleveland, 1954a).
[VI. VIRUSES ASSOCIATED WITH COCKROACHES]
Annotations on some of the following observations may be found in Roth and Willis (1957a). Use of asterisk is explained in footnote [3], page [4].