GEOGRAPHICAL VARIATION OF PUPAL DIAPAUSE IN THE GREAT MORMON BUTTERFLY, PAPILIO-MEMNON L (LEPIDOPTERA, PAPILIONIDAE), IN WESTERN JAPAN

The distribution of the great mormon butterfly, Papilio memnon L., has been expanding to northeastern areas in the Kinki district in western Japan. To investigate the relationship between the phenomenon and cha racteristics of diapause of this species, the photoperiodic response o f 4 Japanese populations including the subtropical and northernmost on es was examined. The critical photoperiod for inducing diapause at 20 degrees C was 12 h 30 min in a subtropical population in Naze City (28 degrees 23'N), and about 13 h in temperate populations in Kagoshima(3 1 degrees 36'N), Wakayama (34 degrees 11'N), and Mine (34 degrees 54'N ) Cities. Latitudinal variation was not found in diapause intensity (9 4-111 days) among the 3 temperate populations. However, diapause incid ence at 13.5L-10.5D, which is slightly longer than the critical photop eriod, increased with latitude of the locality, and the deepest diapau se was observed in some individuals in the Mine population. Neverthele ss, the differences in critical photoperiod and diapause intensity amo ng populations was smaller than that among broods in each population. As it appears to be difficult to explain the recent northward invasion of this species only by this slight change in diapause trait, the inf luence of climatic warming on the phenomenon is also discussed.