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[Vol. 88 
release of alates in worker-reproductive colonies occurs syncronous- 
ly with (or at least in the same season as) queenright colonies. 
As for the remaining species in the impressa group, only 
queenright nests are known in purpurea and this species shows a 
brood development pattern similar to the three others. By contrast, 
distinct winged queens are unknown in enigmatica (all recorded 
colonies worker-reproductive), and this species diverges from its 
closely related congeners by releasing most alates in the fall, 
although males were found overwintering in one nest. The limited 
information indicates a possible relaxation of synchrony in the 
release of ergatoid-seeking male alates, a pattern which would be 
predicted with the loss of the winged queen caste, especially if the 
sexual calling behaviour of ergatoid gynes is temporally dispersed. 
This trend is continued in some other Rhytidoponera species 
outside the impressa group, in which functional queens are rare or 
absent, and flights of alates (males) are reported to be highly non- 
specific with respect to season (Brown, 1958; Haskins & Whelden, 
1965; Haskins, 1979). However, since most of the data come from 
lab colonies of one species ( metalliea ) additional field observations 
are desirable. 
Scattered collections of colonies from different times of the year 
may give a misleading impression of patterns of alate production. In 
at least two species of the impressa group, alates can be found in 
some nests from February to November. Although this superficially 
suggests aseasonal production of alates, a detailed examination of 
brood development demonstrated that only one crop of alates is 
produced each year and that alates are released over a limited time 
period. Additional field studies are necessary to determine whether 
brood development in Rhytidoponera species without queenright 
colonies is less constrained by the need for synchronous alate 
release. For comparison with the impressa group, such studies 
would be most appropriately directed towards other species of east 
Australian mesic forests, in order to minimize climatic and other 
environmental differences. 
Summary 
In the Rhytidoponera impressa group there are two kinds of 
colonies, which are distinguished by the type of reproductive female 
present: queenright colonies with a single dealate queen, and 
