A Latitudinal and Obligatory Diapause Response in Three Subspecies of the Eastern Tiger Swallowtail Papilio glaucus (Lepidoptera: Papilionidae)

Diapause of the Eastern tiger swallowtail butterfly Papilio glaucus is dependent on latitude and subspecies origin. Lower latitude populations of two subspecies, P.g. australis and P.g. glaucus, show little diapause response to a long-day exposure of larval L:D (light:dark) 16:8 at 23.5/19.5 C. Higher latitude populations of P.g. glaucus diapause at the 50% level under this long day regime. Approximately all individuals in populations of the northernmost subspecies, P.g. canadensis, diapause under L:D 16:8, longer photoperiods, even in warmer constant temperatures. This response implies that diapause in P.g. canadensis is obligate. Subspecies isolation may explain differences observed in photoperiodic response.