BIOTIC ASSOCIATIONS OF COCKROACHES — ROTH & WILLIS 97 



of cockroaches and other insects have been published by Glaser 

 (1930b), Schwartz (1935), Steinhaus (1946, 1949), Buchner (1952, 

 1953) » Brooks (1954), and Richards and Brooks (1958). The 

 reader is referred to these papers, and those of authors cited in the 

 Hst at the end of this section, for discussions of the morphology 

 of the bacteroids, their distribution within the host, and attempts to 

 culture them in vitro. 



It has long been assumed, without proof, that cockroaches and their 

 bacteroids form a mutually beneficial association. As it has not been 

 possible to cultivate bacteroids apart from their cockroach hosts, it 

 may be assumed that the host is essential to the continued existence 

 of the microorganism, which also derives from the association other 

 obvious benefits as well. Experiments to show that the host also 

 benefits from the association have centered around rendering cock- 

 roaches bacteroid free. Starvation, parasites, electromagnetic radia- 

 tion, heat or cold, or chemicals have all been used in attempts to 

 eliminate the bacteroids. Of these, only chemical treatment has pro- 

 vided a satisfactory technique. 



Few chemicals other than antibiotics have proved to be useful in 

 the elimination or reduction of bacteroids. Yetwin (1932) injected 

 various dilutions of 22 compounds into Blattella germanica. He ob- 

 served decreases in the bacteroids of the fat body only following 

 injection of methylene blue, but did not pursue this lead further, 

 Gier (m Steinhaus, 1946) observed reduction in the numbers of 

 bacteroids after cockroaches were injected with crystal violet, hexyl- 

 resorcinol, or metaphen. Bode (1936) reported that injection of 

 irritants such as lithium salts or quinine hydrochloride had no ap- 

 parent effect on the symbiotes. 



Brooks (1957) reared Blattella germanica on diets containing dif- 

 ferent concentrations of inorganic ions. On a manganese-deficient 

 diet the cockroaches grew poorly and some of their progeny lacked 

 normal bacteroids ; about 10 percent of the aposymbiotic generation 

 grew and reproduced on a diet fortified with yeast. Varying the con- 

 centrations of other salts in the diets gave results in which the 

 progeny were either aposymbiotic or the fat body was abnormal but 

 the mycetocytes were abundant ; all these cockroaches soon died even 

 on fortified diets. 



The administration of certain antibiotic drugs has produced cock- 

 roaches very nearly free of bacteroids. Brues and Dunn (1945) found 

 that although sulfa drugs had no effect on the bacteroids, penicillin 

 in large doses reduced the number of bacteroids in Blaherus craniifer, 



