Evidence showing that intestinal bacteria contribute to the nutrition of cockroaches is meager. Cleveland et al. (1934) isolated a bacterial organism from the foregut of the wood-feeding cockroach Panesthia angustipennis. The bacterium digested cellulose rapidly in vitro and these workers believe that this cockroach and other related wood-feeding species are dependent on symbiotic bacteria for the digestion of their food.
Mencl (1907) described cell nuclei in "symbiotic," not closely defined types of bacilli that he found in abundance in the digestive tract of the Küchenschabe, Periplaneta (presumably Blatta orientalis). Unfortunately, he was more concerned about the morphology of the bacteria than the stated mutualistic relationship, so nothing is known of their physiology.
The growth rates of Periplaneta americana and Blattella germanica were retarded when the insects were reared aseptically, which suggests that microorganisms normally found in the digestive tract supply certain necessary dietary constituents (Gier, 1947a; House, 1949). Noland et al. (1949) suggested that microorganisms in the digestive tract of B. germanica synthesized riboflavin since the nymphs reared on a low riboflavin diet accumulated more of the vitamin than could have been ingested in the diet. However, Metcalf and Patton (1942) found little or no bacterial synthesis of riboflavin in P. americana. Noland and Baumann (1951) suggested that methionine, one of the amino acids essential for rapid growth of B. germanica, was synthesized by intestinal microorganisms in the insects.
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).