Abstract
The thermal relations of development of the diamond-back moth, Plutella xylostella, were compared for three different local stocks in Japan (Sapporo, Hiratsuka and Kagoshima) and one from Djawa (Batu, Malang). The threshold temperature and thermal constants for development of one generation were calculated from the regression of the velocity of development from the egg to adult emergence on temperature. The Hiratsuka stock had the highest threshold temperature of 9.5°C, and this was followed by the Malang stock with the threshold of 8.6°C, while the Sapporo and Kagoshima stocks showed comparatively lower values, 7.5°C and 7.4°C, respectively. Variation in the thermal constants showed the reversed tendency; the Sapporo stock had the maximum value of 313 degree-days, the Kagoshima (294 degree-days) and the Malang (250 degree-days) stocks followed this, and the Hiratsuka stock took the minimum of 229 degree-days. There was a negative correlation between the threshold temperature and thermal constant. The local difference in the regression of the velocity of development on temperature was tested by means of covariance analysis, which revealed that the regression coefficient (b) was significantly different between the Hiratsuka and the Sapporo stocks, and between the Hiratsuka and the Kagoshima stocks. Furthermore, there was a significant difference in the regression intersect (a) between the Sapporo and the Malang stocks; however, no significant differences existed among any other combinations of the stocks. These results seem to imply that there is a slight local differentiation in the developmental characteristics. The differentiation, however, is not related to the geographical location, nor to the climatic gradient.
