INTERSPECIES COMPATIBILITY
We agree in essence with Chopard (1938) who stated that it is improper to speak of associations apropos of the ecological distribution of Orthoptera. He continued that it is clearly evident that different species of Orthoptera, which are found grouped on a territory more or less narrowly limited, have no interdependence among them. Their grouping results uniquely from almost similar reactions to the different factors which characterize this limited milieu. There is neither interdependence nor interaction; the grouping is a false biocoenose, born under the action of the environment, and does not survive a modification of this milieu.
However, as there are numerous examples of mutual toleration between different species as well as examples of incompatibility, the subject has more than academic interest even if no true ecological significance. On the other hand, further study may show that certain of these associations are definitely ecological, particularly among the feral species. As might be expected, most of the following examples pertain to domiciliary cockroaches.
Dozier (1920) occasionally found Periplaneta americana with Eurycotis floridana in decaying stumps, beneath loose bark of decayed trees, and beneath corded wood. Adair (1923) stated that in his house in Egypt Periplaneta americana, Blatta orientalis, and Blattella germanica were found together in a cupboard. Sambon (1925) found B. orientalis and B. germanica side by side but not fraternizing in a home in Italy. Gould and Deay (1938) observed that apartments over stores were infested with both B. germanica and P. americana, but did not indicate whether these occupied the same microhabitat. Gould and Deay (1940) observed that in the Purdue University greenhouse Periplaneta fuliginosa was found "under benches, boxes, pots and other objects in association with the American roach." Dr. L. A. Hetrick (personal communication, 1954) wrote us that several summers before he had had a mixed infestation of cockroaches, which included Periplaneta australasiae, Periplaneta fuliginosa, and Pycnoscelus surinamensis, in his chicken shed.
Eads (personal communication, 1955), in response to our inquiry about the mixed populations of cockroaches that he had reported infesting sewers in Texas (Eads et al., 1954), stated that "Each of the ten colonies of B. orientalis found in Tyler manholes were associated with larger colonies of P. americana. True breeding colonies of B. orientalis appeared to be present since all the developmental stages were taken. The same situation existed with the P. fuliginosa and the two species of Parcoblatta. Larger colonies of P. americana were associated with the other species in each case. From our limited observations the two species always appeared to be perfectly compatible." Eads et al. (1954) had found Periplaneta fuliginosa in three manholes, Parcoblatta bolliana in one manhole and Parcoblatta pensylvanica in one manhole. We assume that the groups of each species were spacially discrete so that they were recognizable as colonies. Dr. T. A. Olson (personal communication, 1958) has observed two or more species of cockroaches in a single structure but never in mixed colonies. Each species was separated physically from the others. Olson concluded that cockroaches of different species do not mingle freely unless forced to do so by some special environmental condition. Pettit (1940) found B. germanica and P. americana similarly separated in the same building or even in the same basement laboratory.
Perkins (1899) found Lobopterella dimidiatipes generally living in company with the young of Periplaneta australasiae in Hawaii. Rehn and Hebard (1914) in Florida found P. australasiae abundant with Periplaneta americana on a quarter-boat. They also noted that the forficulid Marava [= Prolabia] arachidis (Yersin) appeared in numbers in a kitchen after dark accompanied by swarms of P. americana. These workers also found Leurolestes pallidus in a fruit store in Key West "where the species was common in a pile of old burlap bags and in cracks under the stands which it shared with one fairly large colony of Blattella germanica, occasional specimens of Holocompsa nitidula, a few specimens of Periplaneta americana, and one specimen of Supella supellectilium." They also found H. nitidula with Blaberus craniifer "between old boards in a woodshed, where nymphs were more numerous than adults."
Rehn and Hebard (1914) stated of Supella supellectilium in Florida that "The females were all taken in cupboards where Blattella germanica was found in swarms." The association in human habitations of S. supellectilium and B. germanica has been reported also by Sein (1923), Puerto Rico; Shaw (1924), Australia; Mallis (1954): "German and brown-banded roaches were often found in the same crevice."; Anonymous (1958), Texas; and Anonymous (1958a), Georgia. Gould and Deay (1940) stated that other species of cockroaches, especially B. germanica, may be found with S. supellectilium in the same part of a building. Yet Shaw (1925) stated that "when Supella supellectilium Serv. invades places already occupied by Blattella germanica L., it tends to oust the latter."
Blaberus discoidalis has been found in homes or in fruit debris in Puerto Rico in company with the more common, domiciliary species Leucophaea maderae, but never in abundance (Sein, 1923; Wolcott, 1950). Illingworth (1915) in Hawaii found Symploce hospes associated with Nauphoeta cinerea, Graptoblatta notulata, and Diploptera punctata.
Hebard (1917) found Aglaopteryx diaphana in a bromeliad on a forest tree in Jamaica together with Nyctibora laevigata and numerous Cariblatta insularis. He also found numerous Aglaopteryx gemma under signs on longleaf pines in Alabama with occasional specimens of Parcoblatta lata. In Virginia he found Parcoblatta uhleriana in a decaying chestnut log with Cryptocercus punctulalus. In Florida he found Latiblattella rehni with Eurycotis floridana and, more rarely, with Periplaneta australasiae under bark of pine trees. In Key West he found Symploce hospes in the cupboard of a hotel with swarms of Blattella germanica and a few Supella supellectilium.
Rehn and Hebard (1927) in their study of West Indian blattids reported finding Neoblattella proserpina in epiphytic bromeliads in Jamaica in company with Neoblattella eurydice and Neoblattella dryas. They also list most of the associations cited by Hebard (1917).
Ramme (1923) reported that he found in Germany four species of Ectobius (lapponicus, lucidus, pallidus, and sylvester) living together in an area about 50 m. by 200 m. Although he had stated that his specimens of E. lucidus were a distinct species in 1923, Ramme (1951) later decided that they were a form of E. sylvester, E. sylvester f. lucidus.
Dow (1955) reported trapping Blattella germanica, Periplaneta americana, and Periplaneta brunnea in houses and privies in south Texas. At our request Dr. Dow (personal communication, 1958) analyzed his records to determine whether there were indications of associations between these species, with the following results:
As stated in my published note, the roaches were at first classified to genus only. The 83 Periplaneta subsequently identified to species represented 28 different collections, 11 from houses and 17 from privies, all in Pharr, Texas. Tabulation of the data shows first that P. americana was taken only once in a house and that P. brunnea was taken only 4 times in privies. Of course this distribution greatly reduces the probability that they would be caught together, and it is not surprising that P. americana was trapped alone in the single house collection. P. brunnea, however, was trapped with P. americana 2 of the 4 times it occurred in privy collections.
To investigate the occurrence of Periplaneta with and without Blattella, an analysis has been made of 560 trap collections taken in 40 houses and 40 associated privies in Pharr, Texas, in weekly intervals (from May 14 to June 23 [1948]). In the houses, Periplaneta and Blattella were caught in the same jar 26 times, Periplaneta alone 12 times, Blattella alone 83 times, and neither genus 159 times. In a fourfold table, the value of chi-square (14.7) is significant and indicates that the frequencies are not proportional. The number of times Periplaneta and Blattella actually occurred together (26) is, however, much larger than the expected number calculated from the row and column frequencies (14.8). In the privies, Periplaneta and Blattella were caught in the same jar 9 times, Periplaneta alone 50 times, Blattella alone 18 times, and neither genus 203 times. In a fourfold table, the value of chi-square (1.95) is not significant but the same type of disproportion is evident and the expected frequency of both genera in one trap is 5.7, lower than the actual frequency of 9. Both immature and adult roaches are included in this analysis.
The above evidence would be more satisfactory if based on more extensive data. There is also a possible objection in that the traps were operated for at least overnight, during which time one species could theoretically supplant another. Of course, it is doubtful that there is anything involved here like territory (in the ornithologists' sense). On the other hand, it is well to consider that Periplaneta and Blattella are both likely to be more abundant in the same type of favorable location and that this factor might offset in part some direct antagonism between the species.
The only known specimen of Ischnoptera podoces was captured in company with the type series of Cariblatta nebulicola, in dead leaf litter in Jamaica (Rehn and Hebard, 1927). In Florida Periplaneta australasiae was often taken in company with Pycnoscelus surinamensis and Eurycotis floridana (Blatchley, 1920).