Effects of microclimate and oviposition timing on prediapause larval survival of the Bay checkerspot butterfly, Euphydryas editha bayensis (Lepidoptera: Nymphalidae)

We tested empirically whether microclimate and relative timing of oviposition affected prediapause larval survival and development rates in the federally threatened Bay checkerspot butterfly, Euphydryas editha bayensis (Nymphalidae). Most mortality in Bay checkerspot butterflies occurs among prediapause larvae. Because phenology of the butterfly’s larval hostplant, Plantago erecta, has been thought to drive prediapause larval survival patterns, we also tested whether P. erecta senescence and density over time varied among microclimatic zones. We found that microclimate had a significant effect on P. erecta phenology. Changes in density of edible P. erecta among microclimatic zones were out of phase temporally, but otherwise were similar. In the year of our study, neither microclimate nor oviposition date tended to affect prediapause larval survival, but both variables had significant effects on prediapause larval development rates. Because temperature and precipitation patterns in the butterfly’s environment vary from year to year, whether microclimate and oviposition date significantly affect prediapause larval survival and development also may vary annually. At least in some years, however, senescence of P. erecta may not cause prediapause larval mortality. Our results support the hypothesis that topographic heterogeneity is critical to the long-term viability of the Bay checkerspot butterfly as well as other species that inhabit temporally variable environments.