350 
Psyche 
[June 
no coincidence that dipterous nest scavengers appear much more 
prevalent in Trinidad, Venezuela, and Colombia than they are in 
Argentina. We assume that cell cleaning has evolved in response 
to these nest associates, which probably often cause the female to 
bring in additional flies and thus prolong the nesting cycle. Cell 
cleaning is known in several species of Bembix (Evans, 1966, pp. 358, 
451), although none of these wasps are known to carry the debris as 
far as Rubrica carries it. 
(4) The mature larva constructs 4-6 pores in the walls of the 
cocoon, but these pores are complex, each consisting of a bilobed 
elevation containing several minute perforations. The construction 
of these pores has not been observed in Rubrica , and the function of 
the pores has not been clearly demonstrated in any bembicine wasps. 
(5) Females spend the night away from the nest, and they have 
been reported to cluster on vegetation, although we have not ob- 
served this. Clustering is known in several genera of Bembicini, 
especially Steniolia and Zyzzyx. Species of Stictia and Bicyrtes also 
spend the night on vegetation, although in all known species of 
Bembix the female sleeps in the nest, and in Microbembex the female 
sleeps in a short burrow apart from the brood nest. 
Thus on the whole behavioral and larval features present a some- 
what ambiguous picture as to the relationships of Rubrica to other 
genera, although they do emphasize that it is a distinctive taxon not 
closely related to Bembix. Of particular interest is the intraspecific 
variation in the behavior of R. surinamensis. The occasional use of 
non-dipterous prey suggests a loosening of the stereotypy of hunting 
behavior, in the direction of the broad-spectrum prey selection of 
some species of Glenostictia or of the total lack of specificity of all 
species of Microbembex. Cell cleaning in R. surinamensis appears 
to be an example of geographic variation in behavior, populations in 
the southern parts of the range apparently having evolved a mechan- 
ism for reducing the success of nest scavengers that northern popu- 
lations have not evolved (at least so far as presently known). Nest 
depth and number of cells are probably related to hardness of the 
substrate, shallow nests with several cells being an adaptive response 
to very hard soil, reducing the time and wear involved in nest con- 
struction. All of these points are deserving of further study by per- 
sons with aggregations of the species at their disposal. Rubrica 
surinamensis is evidently one of the most successful of South Ameri- 
can solitary wasps, and a more thorough knowledge of its biology 
may teach us much about the origin and adaptiveness of behavioral 
attributes. 
