176 
Psyche 
[September 
Table 2. Relative abundance of butterflies in possible mimicry complexes 
at Baja la Hondura and Cuesta Angel, Costa Rica 
Month 
No. successive* 
days sampled 
(N) 
1 Mean number of individuals 
D. virgo I. Caesia 
seen b 
O. zelica 
July 
S 
Bajo la Hondura 
9 
0 
16 
August 
12 
7 
0 
15 
July 
10 
Cuesta Angel 
10 
44 
18 
August 
12 
8 
30 
21 
“Sampling was conducted for 1 hour each day; see text for further descrip- 
tion of technique. 
b Given are the mean numbers of adults (both sexes) seen at sampling sites 
. . . per day (9:30-10:30 AM) 
ah, 1971). While these advantages of a shortened larval period are 
clearly adaptive, another adaptive role of this effect is an increased 
reproductive fitness resulting from the shortening of the life table 
parameter, age-to-first reproduction. Adult females experiencing 
selection pressures to lay eggs on young leaves promote this advan- 
tage in life table structure of natural populations. 
Changes in oviposition site-selectivity with seasonal changes in the 
availability of young leaves of herbivore host plants in the tropics 
offer an interesting system to approach the general question of how 
developmental changes in leaf biochemistry can alter the palatability 
of the herbivore, assuming that palatability is at least in part de- 
rived from host plants. If we may reach beyond the data in Table 1 
for D. virgo f there exists the possibility of variation in palatability 
depending on whether or not it underwent larval development on 
old or young leaves of the host plant. Depending on the time of 
year and a host of local edaphic factors which affect the vegetative 
growth pattern of the host plant, a herbivore population may vary 
tremendously in the proportion of palatable and unpalatable individ- 
uals. This, of course, assumes that differences in toxicity occur be- 
tween young and old leaves within a plant population. Recent 
discussion (Levin, 1971) indicates that there can occur both quanti- 
