Abstract
The head capsule width of larvae of Pieris rapae crucivora collected in cruciferous crop fields at Hirosaki, Shimokita and Central Hokkaido in 1962 and 1963 was measured by the authors. The frequency distributions of the measurements represented five separated peaks. Remarkable diferences in head width of each instar were not observed among the larvae collected from different crop fields or at different seasons in the same locality and also among those from different localities. However, the range of individual variation was narrower in the Central Hokkaido population than in the Shimokita and Hirosaki ones. The growth ratio of head width between the first and second instars was the largest, and it gradually decreased in the later instars. The GAINES and CAMPBELL'S formula fitted more precisely to the growth of head capsule width of P.rapae crucivora larvae measured in this report, compared with the DYAR'S or the TOKUNAGA'S formula of insect growth.
