1988] Passer a, Keller, & Suzzoni — Iridomyrmex 63 
— In queenless colonies, female brood may develop into queens at 
any time of the year. 
— Male brood always exists in societies and generally develops 
into males when the societies are dequeened. 
These three conditions being infrequently connected within a spe- 
cies renders queen replacement a rather rare phenomenon in ants. 
Summary 
When experimental societies of the polygynous ant Iridomyrmex 
humilis were dequeened, they produced both male and queen larvae. 
This production of sexuals may occur at any time, because the 
differentiation of sexuals is not connected with overwintering of the 
brood. 
The emergence of queens occurred about 70 days after queen 
removal, whereas males emerged generally earlier. Since mating 
flights are lacking in this species, the newly-produced virgin queens 
and males copulated within the nest less than 8 days after emergence 
of queens. Then newly inseminated queens began to lay eggs rapidly 
after mating and the first callow workers emerged 50 days later. 
This form of social regulation is rather uncommon in ants. Fac- 
tors allowing this regulation are discussed. 
Acknowledgments 
The study was supported by a grant of the University of Lau- 
sanne. Our special thanks are due to Dr. E. L. Vargo (University of 
Texas) for helpful criticisms and for English language editing. 
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