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[Vol. 93 
gland secretions also work as a long-distance attractant. In addition 
to signalling sexual receptiveness to the males inside the nests, these 
volatile secretions (which are produced by many workers) may dif- 
fuse out of the nests and be perceived by searching males. 
Males of O. berthoudi need to enter foreign nests in order to find 
sexual partners. The colony units have distinct identities (Peeters, 
1984), and alien males are recognized as different by workers, which 
then attempt to remove them from the nest; similar hostility is also 
displayed in R. chalybaea (Ward, 1981). This aggression contrasts 
with the acceptance of alien males by workers in ponerine species 
with ergatoid queens, e.g. males in Leptogenys and Megaponera 
were not attacked following their entry into foreign colonies 
(Wheeler, 1900; Longhurst and Howse, 1979). In the queenless 
Dinoponera gigantea, Overal (1980) observed a male being carried 
into a nest by a forager. Carrying of males in O. berthoudi was 
always between the nests of a single polydomous colony and is thus 
not equivalent to the observations made by Overal. Access by males 
to foreign nests may be facilitated by the fact that the older workers 
that perform activities on the surface and are responsible for the 
evictions, are usually not active during the daily peaks of male 
activity. The younger workers confined inside the nests are those 
likely to become mated (Peeters and Crewe, 1985), and these 
probably do not behave aggressively towards foreign males. 
If the queenright ancestors of this species exhibited the typical 
formicid pattern of reproduction, then male and female reproduc- 
tives would have been produced seasonally. With the change to 
worker reproduction, the sexually-attractive workers do not dis- 
perse from their nests prior to mating, and mating is no longer 
coupled with colony foundation, hence the times of male activity no 
longer need to be synchronized with female activity periods or with 
appropriate environmental conditions for colony foundation. This 
relaxation of the selective pressures on the timing of male dispersal 
has resulted in an extended mating period. Nonetheless, male activ- 
ity remains seasonal. This has no adaptive significance in O. ber- 
thoudi, because young workers that can be mated occur throughout 
the year. However it has the effect of ensuring that an adequate 
number of infertile workers are present in the colonies. 
