1981] Topoff, Rothstein, Pujdak, & Dahlstrom — Army Ants 159 
depend upon the “alimentary condition prevalent in the brood” 
(Schneirla and Reyes, 1969), and that emigrations are likely to begin 
soon after food has run low. 
In a recent series of field and laboratory studies of nomadic 
behavior in nearctic colonies of N. nigrescens (Topoff and Mirenda, 
1980 a,b; Mirenda et al., in press), we demonstrated: (1) that the 
location of booty clearly influences the direction of raiding and 
therefore of emigrations; and (2) that artificially-fed colonies exhibit 
a lower frequency of emigrations. The present study differs from 
these in that food augmentation began late in the statary phase, 
before most of the callow population had eclosed. In addition to 
delaying the onset of the nomadic phase by reducing excitation from 
newly-eclosed callows (Topoff et ah, 1980a), this was our first 
attempt to eliminate emigrations through a complete nomadic phase 
in the field. 
During the six days of food augmentation for colony no. 1, we 
provided a total of 144 g of booty. Since the colony generated few 
additional raiding columns, the artificially-administered booty 
represents over 90% of the colony’s total food intake for that period. 
According to Mirenda et ah (1980), colonies of N. nigrescens gather 
approximately 0.4 mg of booty/ larva/ nomadic night. Thus, on the 
average, we provided colony no. 1 each night with an amount of 
food that would be collected by a colony containing about 60,000 
larvae. Although our estimate of colony size contains an error of ± 
20%, we can be reasonably certain of having provided this colony 
with about 1.2 times the amount of food it would normally gather. 
Although the large size of this colony dictated that we could no 
longer supplement its food to the same degree throughout the 
remainder of the nomadic phase, the evidence from phase length, 
callow pigmentation, and larval size supports the conclusion that 
the onset of the nomadic phase was delayed for 4-8 days. 
For colony no. 2, which was considerably smaller and more 
precisely counted, intensive overfeeding was more feasible. On the 
average, 8.8 g of booty were provided on food-supplemented nights. 
This is more than 5 times the amount of food that a colony of this 
size would collect in the field. In view of this feeding regime, it is not 
surprising that the colony conducted only one completed emigration 
throughout its 14-day nomadic phase. We must emphasize, how- 
ever, that a reduction of the frequency of nomadic emigrations is by 
itself not sufficient to infer a relationship between food supply and 
