98 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I4I 



but the cockroaches died within a few days. Death was attributed to 

 lack of bacteroids rather than effect of the drug; this is perhaps an 

 unwarranted conclusion in view of the survival of aposymbiotic cock- 

 roaches that have been produced by other drugs (Brooks, 1954; 

 Brooks and Richards, 1955). Glaser (1946) found that the bacteroids 

 of Periplaneta americana could be adversely affected or destroyed by 

 sulfathiazole, or sodium or calcium penicillin. Fraenkel (1952) ques- 

 tioned the conclusions of Brues and Dunn (1945) and of Glaser 

 (1946) because of the high mortality in their experiments, and he 

 suggested that the described phenomena "were due rather to direct 

 toxic effects on the host than to loss of the symbionts." Noland (in 

 Brooks, 1954; Brooks and Richards, 1955) confirmed Glaser's results 

 with penicillin and extended sulfa treatments to include Blattella 

 germanica. Every female whose bacteroids were reduced to the 

 vanishing point resorbed her ovaries and was incapable of reproduc- 

 tion. Brooks (1954; Brooks and Richards, 1955) found that adminis- 

 tration of several antibiotics did not eliminate the bacteroids from the 

 fat body oi B. germanica unless the dose was so high that it caused 

 excessive mortality. Frank (1955, 1956) was able to eliminate bac- 

 teroids from Blatta orientalis by injecting or feeding chlortetracycline, 

 oxytetracycline, or penicillin ; survival of treated insects was not good 

 and reproduction was poor ; the aposymbiotic individuals were smaller 

 than normal. As Richards and Brooks (1958) have pointed out, it is 

 uncertain how much of this difference was the result of loss of 

 bacteroids and how much the effect of the drug. It is obvious that in 

 all these experiments the action of the drugs on the bacteroids was 

 accompanied by equivocal side effects which confused interpretation 

 of the results. The effect on the cockroach of a loss of bacteroids 

 cannot be separated from a possible toxic effect of the drug. 



Fortunately Brooks (1954; Brooks and Richards, 1955) obtained 

 completely aposymbiotic offspring from Blattella germanica that had 

 been reared on aureomycin. These bacteroid-free nymphs were prac- 

 tically incapable of growth on a natural diet that was adequate for 

 nymphs with symbiotes. However, the addition of large amounts of 

 dried yeast to the diet enabled aposymbiotic nymphs to mature in two 

 to three times the period required by normal nymphs. Final proof 

 of the function of the bacteroids was obtained by reestablishing them 

 in aposymbiotic cockroaches. The insects that received implants of 

 normal fat body of B. germanica showed a slow, steady gain in weight 

 over the controls (Brooks, 1954; Brooks and Richards, 1956). Ob- 

 viously, the intracellular symbiotes subserve the normal nutrition of 

 the cockroach. Whether the bacteroids produce only vitaminlike sub- 



