Larval diapause termination of Monochamus alternatus Hope (Coleoptera: Cerambycidae) under natural conditions

To determine the time of diapause termination of Monochamus alternatus larvae under natural conditions, debarked bolts of Pinus thunbergii and P. densiflora inhabited by diapausing larvae within the xylem were transferred from outdoors to constant conditions of 25°C, 90-100% R.H. and 16L-8D between December 15, 1989 and April 18, 1990. The females required longer incubation time than the males to emerge as adults. The mean incubation time for both sexes to adult emergence decreased as the start of incubation was delayed from mid-December through mid-February, and became constant when the incubation was started between mid-February and mid-March. Larval diapause was thus terminated by mid-February. In pine bolts transferred earlier, a small number of yellow larvae survived in pupal chambers even after a 113-144 day incubation. The proportion of such larvae decreased from 12 % to 0% as the start of incubation was delayed.