Stage-Dependent Changes of the Prothoracicotropic Hormone (PTTH) Activity of Brain Extracts and of the PTTH Sensitivity of the Prothoracic Glands in the Cabbage Armyworm, Mamestra brassicae, before and during Winter and Aestival Pupal Diapause

Abstract

The cabbage armyworm, Mamestra brassicae, enters winter and aestival diapause in the pupal stage under 10L-14D and 16L-8D, respectively, at 23°C. It develops without pupal dormancy under 14L-10D at 23°C. In 6th-instar larvae, the hemolymph ecdysteroid titers as well as the activity and sensitivity of the prothoracic glands (PGs) were nearly the same in the diapause- and nondiapause-programmed larvae. In non-diapause pupae (ND-pupae), the ecdysteroid titer peaked in the first half of the pupal stage. By contrast, in winter and aestival diapause pupae (WD- and AD-pupae), the ecdysteroid titer remained low after pupation. The ecdysteroid titer in diapausing AD-pupae was 8- to 10-times higher than that in diapausing WD-pupae. PGs from 5th-instar and 6th-instar larvae, as well as those from pupae, secreted ecdysteroids and showed a far stronger response to big prothoracicotropic hormone (PTTH) than to small PTTH in vitro. PG activity and its sensitivity to big PTTH fluctuated in a stage-dependent manner, and the pattern was nearly the same for 6th-instar larvae committed to develop into ND-, WD- or AD-pupae. When ecdysteroids for larval-pupal metamorphosis appears in the hemolymph of 6th-instar larvae, the activity and sensitivity of the PGs may be suppressed quickly. After pupation, the titer of hemolymph ecdysteroids as well as the activity and sensitivity of the PGs may be related to the strength (or duration) of pupal dormancy which differs between WD-pupae and AD-pupae.