Louis M. Roth

“ 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. ”

“ Among the other wasp parasites (Encyrtidae, Eulophidae, Eupelmidae) of cockroach eggs many individuals develop in a single oötheca. When a hundred or more wasps emerge from an oötheca which contained less than 20 eggs, it is obvious that a single cockroach egg supported more than one wasp, yet it is possible that one particular wasp larva may have fed upon more than one cockroach egg before becoming an adult. We consider all entomophagous wasps that develop in cockroach oöthecae to be parasites rather than predators. ”

“ In 1859 Darwin (1887) stated that "In Russia the small Asiatic cockroach [Blattella germanica?] has everywhere driven before it its great congener [Blatta orientalis?] ." Yet in France Girard (1877) suggested that the oriental cockroach be introduced into a restaurant infested with the German cockroach as the best way to expel the latter, because the more robust species drives away cockroaches of smaller size. Wille (1920) in Germany found usually only one species of cockroach in a house. ”

“ That the control of domiciliary cockroaches is far from satisfactory may be inferred from current entomological and pest-control journals in which new insecticides are continually advocated to replace others found to be inadequate. Possibly new approaches to the control of cockroaches are needed. Whether these lie in the direction of increased use of parasites and predators for the biological control of these insects remains to be seen. In any event, the more we know about any insect, especially its ecology, the greater the likelihood of achieving satisfactory control. ”

“ In fact, it is almost impossible, despite good housekeeping, to keep any structure used by man free of all food suitable for cockroaches.
That the requisite temperature, water, and food are provided, more or less adequately, by a variety of structures is attested by the innumerable infestations of cockroaches that develop when control measures are relaxed. Within structures the accessibility of certain harborages to cockroaches probably depends on the habits of the species and to some extent on their size. ”

“ We are indeed ignorant of even the identity of fully half and probably much more than half the total number of insect species. Of those that have been described, we have reasonably complete information about the behavior and basic environmental relationships for only a comparative few. The great majority of the remainder are known only from specimens found in museum collections. Such information as we have about these species usually amounts to no more than date and locality of collection.
This is true of the cockroaches, which now include approximately 3,500 described species. ”

“ Nesting sites are holes in palm trees, galleries of beetles, or tunnels in ground. The wasp first seizes a cockroach by the edge of its thorax and stings it in the thoracic region, then seizes the cockroach by an antenna and pulls and leads it to the nest. The wasp deposits her egg on the outer surface of the femur of the cockroach's midleg. The nest is closed with debris; later the cockroach recovers from the sting. The wasp larva first feeds externally, then bores into the cockroach and devours the internal organs. Pupation occurs inside the exoskeleton of the cockroach. ”

“ Have cockroaches been ignored in fauna collections from North American caves, or has our cave fauna been less extensively studied than that of other parts of the world?
The two species of cockroaches found in mines (Blattella germanica and Periplaneta americana) are also found in caves. For this reason we have included them in the list headed Cavernicolous Cockroaches. On the other hand, the cockroaches found in animal burrows are generally different species from those found in caves, so we have grouped these together in a second list. ”

“ The validity of a host-parasite or predator-prey record is dependent upon the accuracy and knowledge of the observer. In assembling these records we have had to accept, in most instances, the identifications of species made by the original authors. However, as a result of our studies on the biology of various species of cockroaches, including some work on their hymenopterous parasites, we have questioned certain records in the literature. ”

“ Ehrlich (1943) has stated that Periplaneta americana exhibits social behavior. For instance, cockroaches of various ages inhabit a fairly large space jointly; the adults and older nymphs sense approaches with their antennae and warn and protect the young by a beating of wings and by body movements. There is complete utilization of the available living space; the imagos drive older nymphs from their resting places, and the older nymphs drive out the younger ones, until all cracks, depending on their size, are occupied by various age groups of different sizes. ”

“ 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 successful 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. ”

“ It is among the so-called viviparous cockroaches that the greatest number of observations have been made of postparturient associations between female cockroaches and their offspring. The females of these species carry their oöthecae in brood sacs within their bodies until embryogenesis has been completed. This behavior ensures protection of the young from desiccation and attack by parasites (Roth and Willis, 1955a) . (See Roth and Willis, 1958a, for an analysis of oviparity and viviparity in the Blattaria.) ”

“ 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 cockroaches bacteroid free. Starvation, parasites, electromagnetic radiation, heat or cold, or chemicals have all been used in attempts to eliminate the bacteroids. ”

“ For example, Ledoux (1945) showed that the species odor is largely responsible for the gregarious behavior shown by Blatta orientalis and Blattella germanica. The olfactory stimulus acts over a short distance only, and the source of this odor in the insect is unknown. By washing Blattella germanica in warm chloroform Dusham (1918) extracted a wax which had the odor of the German cockroach. However, there is no evidence to show that cockroaches respond to the same cockroach odors that are detected by man. ”

“ Movement of cockroaches between habitats may be assumed to occur; but movement from an unfavorable environment to a more favorable one, following a shift in water balance, has not been observed in nature; however, laboratory experiments suggest that the mechanism for mediating such behavior is present in some species of cockroaches (Gunn and Cosway, 1938; Roth and Willis, 1952a) . Obviously, additional research is needed on the bionomics of all species. Further conclusions based on current limited knowledge can only be speculative and possibly misleading. ”

“ The extent of host selection varies among these parasites; some species will oviposit into the eggs of more than one species of cockroach, but others show some degree of host specificity. Positive selection of specific hosts by certain parasites appears in correlative data from different investigators on pages 235 to 254. There is a small body of data that shows nonacceptance of certain hosts by some of these wasps. For example, Comperia merceti would not parasitize eggs of Blatta orientalis or Periplaneta americana in the laboratory (Lawson, 1954a) . ”

“ Behavior.—The female wasp pounces on the cockroach and stings it into immobility; she carries her prey in flight to the nest. Two to 13 cockroaches may be found in one nest; and one or more wasp eggs may be deposited in one nest. The egg is attached at one end to the host's thorax behind a forecoxa. Nest is sealed with dry pellets of soil. The cockroaches apparently do not recover from the wasp's sting. ”

“ Our detailed knowledge of cockroaches is based on studies of the few domiciliary pests that man attempts to eradicate. Comparable studies of the bionomics of the less-well-known species should add much valuable information to our knowledge of this ancient group.
Our understanding of most predator-prey and parasite-host relationships has barely progressed beyond the taxonomic stage. The total effect of predators and parasites in limiting natural populations of cockroaches remains to be determined. ”

“ Soft, juicy fruits and vegetables can provide both moisture and food. There seems to be a tendency for certain species (Blatta orientalis and Blattella germanica) to become established in the more humid parts of structures, such as basements, around sinks, and in bathrooms. Whether this is a reaction to a preferred humidity or merely a fortuitous aggregation near sources of drinking water and food has never been clearly demonstrated. ”

“ Later, after finding that L. maderae is ovoviviparous, Bordage (1913) admitted having misidentified a parasitized oötheca from some other species; he concluded that the developing eggs of this species are protected against egg parasites because they are carried within the female. Clausen (1940) , in classifying the placement of parasitic wasp eggs in relation to the host, erected the category: Egg placed in the embryo while the latter is still within the parent. He stated that although this behavior was not definitely known to occur, it probably could occur. ”

“ Intestinal nematodes of the family Thelastomatidae have no apparent pathological effect on their cockroach hosts. Galeb (1878) has shown experimentally that oxyurids eat the same food as the host insect and that if one starves them, by withholding food from the host, the oxyurids die and disappear. In other words, these worms are not parasites, in the sense that we use the term in this paper, but commensals. ”

“ Natural prey.—Blatta orientalis, U.S.A. (Roth and Willis, unpublished data, 1953) : Dermestes ater is generally a scavenger, but we have seen adult beetles, which had developed in our cockroach colony, clinging to and feeding on living oriental cockroaches, eventually killing them; the beetles probably attack only the weakened or injured cockroaches in a culture. This was a natural infestation of a laboratory culture by a predator. ”

“ The females of many species of cockroaches insure varying degrees of protection to the developing young in their ways of disposing of the oötheca after it has been formed. The extent of this association between the mother and her developing progeny varies from the minimum amount of time spent by oviparous females in concealing their oöthecae, to the duration of embryogenesis in the so-called viviparous species, a period of over a month or more. ”

“ We (Willis et al., 1958) have confirmed the above observations that Blattella germanica, Blatta orientalis, and Periplaneta americana complete nymphal development in less time when reared in groups rather than individually. We (loc. cit.) also found that nymphs of the following additional species matured more quickly when reared in groups: Eurycotis floridana, Periplaneta fuliginosa, Supella supellectilium, Nauphoeta cinerea, and Pycnoscelus surinamensis; only a very slight decrease in the average length of the developmental period was found in grouped nymphs of Leucophaea maderae. ”

“ Watson (1907) stated that Blatta orientalis, Periplaneta americana, and Periplaneta australasiae were injurious in the tropical plant houses at Kew: "at night they come out and run or fly about among the plants, devouring flowers and leaves like rabbits. Such plants as Eucharis, Crinum and Alpinia, when in flower, have little chance in the palm house, where the cockroaches are most abundant; they also find out the ripening bananas and soon devour them." ”

“ Whole families of cockroaches may be found in bromeliads in Brazil (Ohaus, 1900) . Hebard (1920) observed a colony of adults and young of Dendroblatta sobrina on a tree trunk in the Panama Canal Zone.
Whether any of the above associations exemplify maternal care for the newly hatched young is questionable. The behavior of the mother, beyond placing her eggs in a suitable location, seems to be entirely passive. The first-instar nymphs are the active partners in these associations, and they may merely be seeking shelter under the nearest convenient object rather than under the mother as such. ”

“ Hafez and Afifi (1956) reported that in Egypt Supella supellectilium attaches its oötheca to a suitable substrate with a gummy oral secretion but leaves the egg capsule otherwise exposed. We (1954) have noticed similar behavior in laboratory colonies of this species and of Blatta orientalis, as have Gould and Deay (1940) . Cornelius (1853) stated that the female of B. orientalis takes care of the safety of her offspring to the extent of usually dropping her oöthecae in places which are dry and raised above the ground, although rarely one also may find some oöthecae scattered on the ground. ”

“ Potential prey that successfully defends itself against attack is never found in a predator's stomach.
[Pg 345]
Cockroaches have a variety of glands which secrete odorous materials. Certain secretions, produced by tergal or dorsal glands in males, are involved in sexual behavior; the females feed on the secretion from these glands prior to copulating (Roth and Willis, 1954) . However, other secretions which are produced by both sexes are ejected or given off when the insect is disturbed; undoubtedly these are defensive weapons that are used against predators. ”

“ Infective larvae of Protospirura muricola, after hatching from ingested eggs, pass through the cockroach's gut wall and encyst mainly in the thorax, around the crop, and at the bases of the large muscles of the prothoracic legs (Foster and Johnson, 1939) . It is probably generally true that nematodes which are secondary parasites in cockroaches do some damage to the host's intestinal tract at least, and they probably also damage other organs in which they may encyst. ”

“ Many details about the lives of even those that share man's habitations are not fully understood. This then is a rough measure of how little is known about cockroaches.
With the exception of mosquitoes and a few other comparatively small groups of insects on which work has been concentrated, it is doubtful if any other comparable segment of the world's insect fauna is better known. Already an estimated 800,000 kinds of insects have been described, and since this figure is generally regarded as less than half the actual total, think what this means in terms of knowledge yet to be assembled. ”

“ It is likely that the smaller wasp egg parasites are more effective than the evaniids in controlling cockroaches. Only one evaniid develops in a parasitized oötheca, but many individuals of the other wasps develop in one oötheca and the number of females that emerge is usually large. However, Cameron (1957) concluded that, with a parasitism rate of 25 to 29 percent and three to four generations a year, against one or less for the host, Evania appendigaster in the areas where it is established is a valuable control agent. ”

“ The wasp larva, being restricted to the inside of the oötheca, is not free-living. Probably the only criterion by which the evaniid could be judged to be a predator, by Clausen's definition, is that more than a single egg is devoured by the maturing wasp larva. ”

“ To show the full extent of the associations, the associates, from bacteroids to vertebrates, are arranged phyletically. These associate-centered classifications serve admirably to relate various species of cockroaches within common bounds, but fail to give an integrated account of the [Pg 16] total biotic relationships in the ecology of each species. Although physically separated in this monograph, the many associates of each species of cockroach should all be considered in appraising the ecology of that species. ”

“ We (1952) had similarly observed that no isolated male of Blattella germanica was ever seen to give a courting response without having received some form of external stimulation. Yet when numbers of males were kept together isolated from females, on several occasions the males became active and a few individuals gave a courting response. As the sexual stimulus is received by the male of B. germanica through contact rather than odor, as in P. americana, presumably it was mutual contact between the grouped males that released the courting activity. ”