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Psyche 
[June 
some species, voltinism patterns as well. The purpose for this work 
is to examine the hypothesis that, of the butterflies in particular 
climatically similar areas, those which have larval food-plants that 
are apparently nutritionally unsuitable for much of the growing sea- 
son will exhibit in general fewer broods per season than those butter- 
flies which have larval food-plants that are apparently nutritionally 
adequate throughout the season. 
Methods 
In order to examine the hypothesis the number of broods produced 
per year by, and the larval food-plants of, eighty-six species of but- 
terflies were tabulated for three transition zone areas in eastern and 
mid-western United States (Forbes, 1906; Saunders, 1932; Ebner, 
1970). Additional food-plant records were obtained from Ehrlich 
and Ehrlich (1961) and Shapiro (1966). The voltinism patterns of 
selected species of these butterflies were then related to changes in 
the nutritional suitability of their larval food-plants. 
Results and Discussion 
That differences in larval growth rates are reflected in the voltin- 
ism patterns of butterflies is seen in the following example. Under 
similar temperature and humidity conditions the duration of the 
larval stage of the imported cabbageworm, Pieris rapae , is about 15 
to 20 days on some of its food-plants (Slansky, 1974), while that of 
the Eastern tiger swallowtail, Papilio glaucus, is about 35 to 45 days 
on some of its food-plants (J. M. Scriber, unpublished data). As a 
consequence, P . rapae generally exhibits one brood more than P. 
glaucus in the areas where they occur together (Table 1).* 
Further support for the hypothesis is found when the voltinism 
patterns of selected butterfly species are examined in relation to sea- 
sonal changes in the nutritional suitability of larval food-plants. For 
example, species whose larvae feed on oaks (Quercus) , such as the 
hairstreaks Satyrium edwardsii, S. liparops , and S. calanus , and the 
skippers Erynnis brizo , E. horatius, and E. juvenalis, usually have 
^Although P. glaucus is generally considered to have two broods in the 
areas surveyed in this study, it may be that there is only one ‘true’ brood. 
It appears that a high percentage of the pupae from the previous season 
emerge in the early summer, constituting the ‘true’ first brood, and that 
the remaining pupae emerge later in the summer, constituting an ‘appa- 
rent' second brood (i.e., not the progeny of the first brood of that season) 
(Scudder, 1889; R. Lederhouse and J. M. Scriber, unpublished data). 
