366 
Psyche 
[September-December 
and other species.) It is also possible that host selection by ovi- 
positing females is closely tied to host plant phenology, and that 
flowering condition of the plants, and possible correlated changes in 
mustard oil concentrations, may determine the patterns observed. 
References 
Ellis, S. L. 
1974. Field observations on Colias alexandra Edwards (Pieridae). 
J. Lepid. Soc. 28: 114-125. 
Emmel, J. F. 
1974. in R. L. Langston. Zone 1. Season Summary, Lepid. Soc. News, 
25 June, p. 3. 
Garth, J. S. and J. W. Tilden 
1963. Yosemite Butterflies. J. Res. Lepid. 2: 1-96. 
Shapiro, A. M. 
1974. Ecological and behavioral aspects of coexistence in six Crucifer- 
feeding Pierid butterflies in the central Sierra Nevada. Amer. 
Midi. Naturalist, in press. 
Tilden, J. W. 
1965. Butterflies of the San Francisco Bay Region. Berkeley and Los 
Angeles: University of California Press. 88 pp. 
White, R. R. and M. C. Singer 
1974. Geographical distribution of host plant choice in Euphydryas 
editha (Nymphalidae) . J. Lepid. Soc. 28: 103-106. 
