Overwintering Stage in the Spotted Cutworm, Xestia c-nigrum LINNE

Abstract

In central Iwate, the summer generation of the spotted cutworm, Xestia cnigrum Linn, passes six larval instars almost always. Number of instars in the overwintering larvae is more variable, and this makes it difficult to define their overwintering stage. Head capsule measurements showed that they entered hibernation at the stage comparable to the 4th or 5th ins tab, mainly the latter, of the summer generation. Low field temperatures in higher lands between 460 and 700m above sea level did not prevent the larvae to reach this overwintering stage. High mortality of overwintering larvae presumably due to parasitic disease was suggested.