Transition of Diapause Attributes in the Hybrid Zone of the Two Morphological Types ofPsacothea hilaris(Coleoptera: Cerambycidae)

Abstract

Psacothea hilaris (Pascoe) is an important pest of mulberry trees in Japan. The subspecies P. hilaris hilaris, which is found in Kyushu, Shikoku, and Honshu, 3 of the 4 main islands of Japan, includes 2 different strains with clearly different seasonal prevalence and stripe patterns on the pronotum of the adult insect (i.e., the ‘west Japan type’ and ‘east Japan type’). Hybridization between the 2 types occurs in nature, because stripe patterns and seasonal prevalence that are intermediate between the 2 types are found at the boundary of the distribution areas. In the current study, geographic variations in stripe pattern of the adults and diapause attribute of the larvae, an important determinant of seasonal prevalence, were examined using populations collected in Tokyo and the surrounding 10 prefectures. Hybridization between the 2 types was widely found in the areas where the east Japan type was once predominant, probably because of the eastward expansion of the west Japan type. The photoperiodic responses of the populations in the hybrid zone were ambiguous and intermediate between the clear long-day response and the nonphotoperiodic response, which characterize the west Japan and the east Japan types, respectively.