Abstract

The Swallowtail (Papilio machaon) is one of the largest and most conspicuous butterflies in Central Europe, occurring in three generations each year. The third generation decides during its caterpillar or pupa stage whether to hatch in the fall or hibernate (by entering diapause, a resting phase in the development of an organism) and hatch in the following spring. This study investigated the external factors that influence this decision. In addition, the decision sensitive period was investigated the first time for P. machaon. It was found that day length (photoperiod) is critical, with the caterpillar making its decision 3-4 days before pupation. The critical day length, at which a diapause occurs in 50% of individuals, is 14 ¼ ± ¼ hours, which corresponds to August 14 (± 5 days) in the Sarner region (alpine region). Caterpillars that pupate before this date usually hatch in the fall, while those that pupate afterwards go into diapause until spring. Future studies could investigate how climate change, with rising temperatures and longer summers with longer vegetation periods, could affect the key date of the P. machaon. The molecular processes that are induced by environmental factors and determine the onset of diapause in Papilio machaon also still require investigation.