BIOTIC ASSOCIATIONS OF COCKROACHES — ROTH & WILLIS 34I 



litter in Jamaica (Rehn and Hebard, 1927). In Florida Periplaneta 

 australasiae was often taken in company with Pycnoscelus surina- 

 mensis and Eurycotis floridana (Blatchley, 1920). 



INTERSPECIES ANTAGONISM 



In contrast to the presumably amicable associations mentioned 

 above, other observations in the literature seem to indicate that some 

 species of cockroaches are incompatible when they attempt to occupy 

 the same habitat niche. Marlatt (1915) stated "Rarely do two of the 

 domestic species occur together in the same house. Often, also, of two 

 neighboring districts one may be infested with one species, while in 

 the other a distinct species is the commoner one. The different species 

 are thus seemingly somewhat antagonistic, and it is even supposed that 

 they may prey upon one another, the less numerous species being 

 often driven out." Phelps (1924) stated "Roaches of different species 

 are rarely found together, although roaches of the same species live 

 together on very amicable terms." 



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. Yet when he placed B. orientalis and B. ger- 

 manica together, there were no reciprocal attacks even by hungry in- 

 dividuals. Wille concluded that because of their greater speed, smaller 

 size, greater number of eggs, and faster development, the German 

 cockroaches eat the available food and so make the environment un- 

 favorable for the oriental. However, he noted that cases may be seen 

 in which the opposite is also possible. Laing (1946; British Museum 

 [Natural History], 1951) observed that in the British Isles B. ori- 

 entalis seems to have lost its dominant position to B. germanica in 

 recent years ; it was stated that these species are not as a rule found 

 together and that the greater rapidity of breeding and ability to climb 

 of B. germanica, as well as the layout of modem buildings, are some 

 of the factors that favor the spread of B. germanica. Ledoux (1945) 

 found that first-instar nymphs of B. germanica and fourth-instar 

 nymphs of B. orientalis, adults of B. germanica and sixth-instar 

 nymphs of B. orientalis, as well as adults of both species, did not form 

 mixed groups. However, when he combined fifth- and sixth-instar 



