Effect of Temperature on Pupal Pigmentation and Size of the Elytral Spots in Coccinella septempunctata (Coleoptera: Coccinellidae) from Four Latitudes in Japan

Abstract

Coccinella septempunctata populations collected from different latitudes in Japan were reared for the first time at three constant temperatures and the size of the central elytral spot was measured. At 20°C the elytral spot size increased with latitude. It was significantly greater in the Sapporo population, 43°N, than in the Tsukuba and Kagoshima populations, which are at latitudes 36 and 32°N, respectively, and smallest in the Iriomote population at latitude 24°N. In all populations the elytral spot increased in size when reared at lower temperature. This tendency was very strong in the Sapporo population. The pigmentation of pupae increased with decrease in temperature, thus they were mostly orange at 30°C and dark brown at 20°C. In agreement with previous reports by DOBZHANSKY and SASAJI, it is assumed that all three populations from the main Japanese islands belong to C. septempunctata brucki. In the Iriomote population, the spot was small and little affected by rearing temperature; this suggests that this population may belong to the subspecies C. septempunctata septempunctata. The contrast between earlier and later reports on the occurrence of the two subspecies in the Ryukyu Islands is discussed in relation to the dense ship transport from the main Japanese Islands after 1972.