Ecological determinants of food plant choice in the checkerspot butterfly Euphydryas editha in Colorado

The larvae of Euphydryas editha in Gunnison County, Colorado, feed on Castilleja linariifolia. Two related plants, C. chromosa and Penstemon strictus, occur in the same area and are equally nutritious, but are not eaten. Restriction to C. linariifolia appears to be a case of ecological monophagy -- survival on the other two species is less likely not because of their biochemical make-up but because of their ecological characteristics, primarily their phenologies.