Variation in Overwintering Pharate Larval Supercooling Points Between Populations of Parnassius clodius (Family: Papilionidae) Inhabiting Two Different Elevations in California

Parnassius clodius, a Snow Apollo butterfly species native to western North America, overwinters as pharate first-instar larvae enclosed within the chorion. Different populations can experience vastly different overwintering temperatures, which are influenced on a microclimatic scale by both snowpack depth and air temperature. Higher elevation populations are likely to experience more moderate overwintering temperatures than lower elevation populations due to the generally greater snowpack volume and stability at higher elevations. Thus, I hypothesized that higher elevation populations would exhibit reduced cold tolerance compared to lower elevation populations, reflected in a higher average egg supercooling point. The results showed that the high elevation population had a supercooling point 0.61 °C warmer than that of the low elevation population (F test, F1,48 = 10.38, P = 0.0023). This pattern supports the hypothesis that overwintering pharate larvae in high elevation populations are less cold-tolerant than their low elevation counterparts and highlights the potential for increased overwintering mortality at high elevations with reduced snowpack under climate change.