1988] 
Heinze & Buschinger — Leptothorax 
317 
nests to search for food and fed their own larvae. Only one single 
gynomorphic queen, however, managed to rear her own workers in 
the second summer after mating; in most cases the brood eventually 
died. 
In the laboratory, supernumerary females have been found to 
survive for several artificial breeding cycles in the presence of the old 
queen. Aggression of the workers toward their young inseminated 
sisters was observed only in colonies with gynomorphs. Here 13 of 
19 females, which had been put back into their mothers’ nest and 
were not given the chance to escape, were killed by workers within a 
few weeks after copulation, their antennae and legs having been cut 
off. The dissection showed that in most of these females the devel- 
opment of eggs had already started and the ovarioles were elon- 
gated. Four other inseminated females were tolerated in this colony 
for at least one hibernation. Foreign inseminated females were never 
tolerated by a colony, regardless of the morpha. 
In several cases, fission of colonies with two or more inseminated 
females occurred after hibernation. Old nesting sites were aban- 
doned and workers moved brood and adults into two or even three 
different new nesting sites. In comparable situations, colonies with 
only one single female usually gathered in one nesting site after a 
few days. Spontaneous fission of colonies with several females, 
however, led in three instances to two independent societies each, 
which did not exchange brood or workers. One colony fused again 
after two breeding cycles, but only after one of the two queens had 
died. 
Queen replacement was observed in five colonies, where a hitherto 
sterile female became fertile after the old queen had died. In two 
colonies, this event was pursued in electrophoretical enzyme analy- 
sis. The esterase locus #7 is variable in Leptothorax spec. A and in 
other related species; its at least four different allozymes can be 
separated by isoelectric focusing (Heinze and Buschinger, 1988). 
Queen replacement was reflected in a change of the esterase geno- 
type of worker pupae. A colony from Baie Ste. Catherine, Que., 
which before had workers with the esterase genotypes BC and BD, 
now reared diploid brood with the genotype AC, too, thus decreas- 
ing the relatedness of workers within the colony. In an additional 
colony from Riviere Romaine, Que., queen replacement led to a 
change in the morpha of young females. Whereas the old queen had 
