RELATIONSHIP OF LARVAL FOOD-PLANTS 
AND VOLTINISM PATTERNS IN 
TEMPERATE BUTTERFLIES* 
By Frank Slansky, Jr.** 
Department of Entomology, Cornell University 
Ithaca, New York 14850 
An interesting aspect of phenology is the number of broods that a 
species produces in the growing season. Even among a fairly uniform 
group like the butterflies within a restricted geographical area, voltin- 
ism patterns of the different species may vary considerably. Explana- 
tions of possible causes of, and ecological implications of these pat- 
terns have apparently seldom been attempted. 
It might be expected that voltinism patterns are often genetically 
determined and are regulated by some environmental clue (cf. Wig- 
glesworth, 1967), but knowing the proximate reason does not reveal 
the ultimate causes that brought the voltinism patterns under such 
control. Obviously, the presence of a food source for the larvae (and, 
although less well studied, for the adults as well) will have a major 
influence on these patterns. The exclusive use of the vernal herb 
Dentaria by larvae of the West Virginia white, Pieris virginiensk, 
precludes any more than one brood per season. As an adaptation to 
feeding on this ephemeral food-plant, the larvae upon entering the 
pupal stage undergo obligate diapause, even though the genetic 
mechanism for multivoltinism exists in this species (Shapiro, 1971). 
A more subtle explanation of voltinism patterns may emerge from 
examining larval growth rates on different plants (e.g. Dowdeswell 
& Willcox, 1961 ; Hovanitz & Chang, 1962; Sharifi & Zarea, 1970). 
Nutritional (including water) differences (Soo Hoo & Fraenkel, 
1966; Waldbauer, 1968; Feeny, 1970; J. M. Scriber and P. P. 
Feeny, ms. in prep.; Slansky, 1974) and differences in secondary 
chemical content (Gupta & Thorsteinson, i960; Nayar & Thorstein- 
son, 1963; Feeny, 1970) of different plant species and of the same 
plant species at different stages of growth in large part determine the 
growth rates of larvae feeding on the plants, and thus perhaps for 
*This work was supported by Hatch Grant NYC-139413 and NSF Grant 
GB-33398. 
**Present address: Department of Zoology, University of Iowa, Iowa City, 
Iowa 52242. 
Manuscript received by the editor April 12, 1974. 
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