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[June 
one, or at most two, broods, and most hibernate in the larval and/or 
egg stage (Table 1). This may be due to the presence in the oak 
leaves of tannins that restrict protein utilization and hinder larval 
development, in many cases limiting consumption of the foliage to 
spring and early summer when the protein content is highest and the 
tannin content lowest (Feeny, 1970). 
In addition, the leaves of many species of shrubs and trees contain 
substantially lower percentages of water than the leaves of many 
annual and perennial herbs (Way, 1853; Fagin & Watkins, 1932; 
Soo Hoo & Fraenkel, 1966; Slansky, 1974; J. M. Scriber, unpub- 
lished data). Since the percentage of water in most lepidopterous 
larvae appears to be about 80 to 90% (Evans, 1939a; 1939b; Wig- 
glesworth, 1967; Slansky, 1974; J. M. Scriber, unpublished data), 
the growth of larvae feeding on plants with a percentage of water 
lower than their own tissue may be limited by the availability of 
water so that they exhibit slower growth rates in comparison to 
larvae feeding on plants that have a percentage of water equal to or 
greater than that of the larvae (Southwood, 1972; J. M. Scriber & 
P. P. Feeny, ms. in prep.). The fact that a number of tree and 
shrub feeders exhibit but one or two broods (Table 1) supports this 
contention. Along these lines Feeny (1974) has suggested that plant 
species that are abundant and/or persistent have apparently evolved 
“quantitative” defenses (low nutrient contents, tough leaves, high 
contents of unspecific chemicals like tannins) that act as significant 
ecological barriers to phytophagous insects, in contrast to plant spe- 
cies that are rare and/or ephemeral that have apparently evolved 
“qualitative” defenses (specific secondary chemicals) that act as only 
slight ecological barriers to adapted insects although having consid- 
erable impact as evolutionary barriers to non-adapted insects. 
The majority of grass- and sedge-feeders (all Satyridae and sev- 
eral Hesperiidae) , with characteristically sluggish larvae (Scudder, 
1889), exhibit but one brood (Table 1). In view of the low moist- 
ure and high fiber content of many grasses (Way, 1853; Watson, 
1951), it is not surprising that larval development might be slow on 
such plants. The hibernation of many of these satyrids and hesperiids 
as early instar larvae (Table 1) may be an adaptation for the avoid- 
ance of nutritionally poor, mature grass plants and for the maximum 
utilization of the spring flush of succulent growth when moisture 
and nitrogen levels are high and fiber content low (Watson, 1951). 
Thus, the voltinism patterns of several butterfly species are given 
an ecological meaning, and the hibernation of many butterfly species 
as eggs, larvae, and perhaps fertile adults (Scudder, 1889), when 
