1921] Wheeler: Some Social Beetles 45 



of the cavity and especially in the rays of nutritive parenchyma. 

 That the very exuberant neotropical fauna comprises a consid- 

 erable number of such enterprising insects, the following obser- 

 vations will show. 



It will conduce to clearness if we divide the insects which 

 take possession of the petiolar enlargements into two series 

 (Plate II). The first series comprises a small number of ants, 

 social beetles and coccids which utilize all the advantages afforded 

 by the petioles, i. e., use them not only as dwellings for them- 

 selves and their young but also as sources of food. Among these 

 three groups of insects the coccids occupy a peculiar and impor- 

 tant position. They are present in considerable numbers and of 

 all sizes in all petioles inhabited by established colonies of the 

 beetles and ants. Specimens of the coccids from petioles of both 

 young and adult trees were submitted to Mr. Harold Morrison, 

 who pronounces them all, without exception, to belong to a single 

 species of mealy-bug, Pseudococcus hromelix Bouche (Fig. 9), 

 a well-known form which has been taken in widely scattered 

 tropical and subtropical localities (India, Zanzibar, Brazil, 

 Florida and even in the hot-houses of Massachusetts) and on a 

 variety of plants (mulberry, Canna, Hibiscus, pineapple). As 

 these insects are, of course, quite unable to make openings in the 

 walls of the petioles, they either wander into the cavities from 

 the surface of the plant, after the ants and beetles have entered, 

 or they are carried in by the former insects. Once inside the 

 petioles the coccids attach themselves to the longitudinal strips 

 of nutritive parenchyma in the walls, insert their beaks and find 

 an abundant supply of sap. The ants can then absorb the saccha- 

 rine excrement ("honey dew") of the coccids and thus vicariously 

 feed on the plant. The beetles, as we shall see, not only utilize 

 this same source of liquid nutriment but also feed on the solid 

 nutritive parenchyma of the petiolar walls. 



The other series, which comprises many more forms, merely 

 use the petioles as nesting, dwelling or hiding places. They enter 

 petioles that have been previously occupied and abandoned, and 

 behave in all respects like the insects which live in old oak-galls 

 in our northern woods. They are in fact merely tenants, or 

 inquilines, or what German zoologists call "Raumparasiten." No 

 coccids are found in the petioles inhabited by these insects, which 



