1988] 
Passera, Keller, & Suzzoni — Iridomyrmex 
61 
because caste determination occurs very early at the beginning of 
the larval stage (Passera and Keller, unpublished data). Conse- 
quently, pupation of female sexuals occurred no earlier than day 32 
and continued as far as day 84 (N = 94; mean ± SD = 56 + 8). 
Winged virgin queens emerged later (N = 28; mean ± SD = 64 + 
12 ). 
Mating and colony growth: At the time of the emergence of virgin 
queens there were always males of varied age because of the broad 
period of their emergence. On the other hand, the number of males 
was always large because the sex ratio favors these later: a total of 
758 male pupae and only 94 queen pupae were produced over all the 
experimental units. 
Of the 38 winged queens monitored, 36 (95%) succeeded in copu- 
lating with males in the nest. This is explained because in this species 
there is no mating flight (Newell and Barber, 1913; Markin, 1970; 
Benois, 1973) and mating usually occurs in the nest. 
In our experimental units, copulation occurred very quickly after 
queen emergence: 5.1 + 1.9 days (N = 36) after emergence queens 
were dealated and egg laying by queens began immediately. The 
number of remaining workers was greatly decreased, but was still 
large enough to rear the new brood. The first callow workers 
emerged about 50 days after queen mating and about 130 days after 
the societies were dequeened. 
Discussion 
The production of virgin queens in queenless societies has been 
demonstrated in a number of species including Hypoclinea quadri- 
punctatus (Torossian, 1967), Plagiolepis pygmaea (Passera, 1969, 
1984), Leptothorax nylanderi (Plateaux, 1971), Leptothorax reced- 
ens (Dejean, 1974), Odontomachus haematodes (Colombel, 1978), 
Camponotus aethiops (Dartigues, 1978; Suzzoni et al., 1986), Myr- 
mica rubra (Brian, 1979, 1983), Solenopsis invicta (Vargo and 
Fletcher, 1986). In all these cases, the new virgin queens were never 
inseminated inside the nest resulting in the failure of the replace- 
ment of the mated queen. The replacement of mated queens has 
been reported in only three species. 
The first case is the red imported fire ant Solenopsis invicta 
(Tschinkel and Howard, 1978). When monogynous colonies in the 
field are orphaned by removing the queens, censuses made several 
