BIOTIC ASSOCIATIONS OF COCKROACHES — ROTH & WILLIS 93 



off without them . . . Small effects such as lack of vitality, loss of 

 voice, excessive blinking, or perverted habits like dirt eating are 

 extremely difficult to gauge. Nevertheless, it is only a question of 

 degree. Potentially all parasites are harmful." It should also be 

 pointed out that some workers would consider certain of our com- 

 mensals of cockroaches to be parasites. Thus Faust (1955) stated 

 that "A truly successful parasite is one which has developed a state 

 of equilibrium with its host, so that no detectable damage is produced 

 which endangers the health or life of the host. In a suitable host the 

 parasite may obtain food and shelter without any evidence of trauma 

 or toxicity. The damage produced may be so slight that repair and 

 functional readjustment keep pace with the injury." Faust's suc- 

 cessful parasite would be indistinguishable from a commensal, but 

 there is undeniably a difference between an organism causing slight, 

 and undetectable, damage to a host and one causing none. Certain of 

 the organisms we list as commensals may eventually be shown to be 

 parasites. 



Certain organisms which live in cockroaches appear to have no 

 effect on the vitality of the host even though the tissues of the host are 

 invaded. Gregarines may penetrate the intestinal wall of the cockroach 

 without seeming to injure the host. Fungi of the genus Herpomyces 

 invade the cuticle of cockroaches producing pathological changes ; yet 

 the insects' behavior is apparently unaffected (see p. 129). We consider 

 these organisms to be parasites because the host's tissues are invaded 

 and, as far as we know, no benefit to the host results. 



In the literature certain insects have been considered to be either 

 parasites or predators or both. Among these are the ensign wasps 

 (Evaniidae), whose larvae feed on the eggs of cockroaches within 

 the ootheca, and the ampulicid wasps, which capture, paralyze, and 

 store in their nests (as food for their larvae) nymphs and adults of 

 cockroaches. Clausen (1940) claimed that the evaniid Zeuxevania 

 splendidiila is a true egg parasite when it destroys the first egg in a 

 cockroach ootheca; but after the wasp larva molts and proceeds to 

 devour the other eggs, he considered it to be a predator. Clausen's 

 definition of an entomophagous parasite is an insect that in its larval 

 stage develops either internally or externally upon a single host which 

 is eventually killed ; with few exceptions the adults are free-living 

 and their food is usually different from that of the larvae. A pred- 

 atory insect, by Clausen's definition, is principally free-living in the 

 larval as well as adult stage, kills the host immediately by direct attack, 

 and requires a number of victims to reach maturity ; the predator is 



