Growth Season Constraints in Climatic Cold Pockets: Tolerance of Subfreezing Temperatures and Compensatory Growth by Tiger Swallowtail Butterfly Larvae (Lepidoptera: Papilionidae).
The combination of limited seasonal thermal unit accumulations (degree days) and freezing mortality or non-freezing cryoinjury from late spring/early fall freezes in climatically constrained areas has been hypothesized to be major determining factors for geographic range limits and degree of polyphagy in herbivorous insects. We test the hypothesis that cold stress such as from sudden freezes has direct or indirect (delayed) negative impact on egg and larval survival and growth of tiger swallowtail butterflies, Papilio glaucus Linnaeus. Nine treatment regimes with three temperatures (-14°C, -8°C, 4°C) and three exposure durations (8h, 24h. or 48h) were tested using 14 different butterfly families. Negative effects were observed for egg viability, 1st instar, 2nd instar, 3rd instar larval survival and growth subsequent to cold treatments, with more serious impact at colder temperatures and longer durations. These results support the hypothesis that, if severe, late spring freezes can select strongly against these vulnerable, non-diapausing stages. However, numerous physiological and ecological adaptations are known to exist for Papilio eggs, larvae, and pupae, which maximize successful completion of the generation before winter. A new one reported here is faster subsequent growth rates in surviving larvae which were exposed to the cold stress for the longest duration.
