1983] 
Calabi, Traniello, and Werner — Pheidole 
407 
used for P. hortensis is applied (rejected behaviors with frequencies 
< 1% of those performed by that physical caste) the number of 
behaviors rejected for P. dentata increases from two to seven of 28 
(N=l,222; Wilson 1976a). Thus the appropriate comparison of age- 
biased behaviors among behaviors with frequencies ^ 1% shows a 
similar situation for the two; 1 3 of 1 7 behaviors for P. hortensis. and 
15 of 19 for P. dentata. Of behaviors performed without apparent 
age bias, allogroom majors and trophallaxis with majors, are in 
common to the two species. (In general ant repertories include high 
proportions of infrequent behaviors: for minors 10 of 28 {P. dentata 
— Wilson 1976a), 27 of 38 {Zacryptocerus varians — Wilson 1976b) 7 
of 28 [Formica perpilosa — Brandao 1979), 14 of 27 [Orectognathus 
versicolor — Carlin 1982) and 9 of 28 [Camponotus sericeiventris — 
Busher 1982). Although some castes have small repertories (majors 
of P. dentata and So/enopsis geminata , — Wilson 1976a, 1978), 
many other castes show similar proportions of infrequent to fre- 
quent behaviors (Wilson and Fagen 1974, Traniello 1978, Brandao 
1979, Carlin 1982). 
2. Age-based division of labor. 
It is a virtual truism that among social insects older workers 
forage and have little or nothing to do with brood care. Yet in P. 
hortensis older workers, in addition to performing all foraging and 
food retrieval (P and Q, Figure 1), show high RPM for several 
brood-care tasks (K, L, M, and O). We suggest that these represent 
labor cohorts, based on ant experience or colony need. They could 
arise via the mechanism of task fixation, a feedback-based task 
stabilizing mechanism documented in wasps (Forsyth 1978) and 
suggested for the ant Amhiyopone pallipes (Traniello 1978). An 
individual performs some task (e.g., trophallaxis with larvae), 
receives positive feedback (continually finds hungry larvae), and 
over time does not switch to other tasks because the positive 
feedback does not cease. The susceptibility of individuals to task 
fixation could vary so that even in a system with age-based task- 
switching, task fixation might override age-based behavioral 
change. 
Although it remains to be demonstrated whether such fixation 
occurs in P. hortensis. we wish to point out one possible con- 
sequence of task fixation and the resultant caste “atypical” be- 
