Developmental landmarks and the activity of juvenile hormone and juvenile hormone esterase during the last stadium and pupa of Lymantria dispar

Abstract

Changes in juvenile hormone and juvenile hormone esterase activity were monitored during the last stadium and pupa of the gypsy moth, Lymantria dispar. Methods were developed to separate the sexes and to stage larvae using morphological and behavioural markers. Juvenile hormone activity determined by the Galleria melonella bioassay was relatively high during the early development of the last larval stadium; the activity was 5 times higher in females (6th instar) than in males (5th instar). Juvenile hormone activity decreased rapidly during the middle of the stadium and further declined shortly before pupation. Low levels of juvenile hormone activity persisted throughout the pupal stage. Three peaks of juvenile hormone esterase activity were observed during the last stadium in both sexes. The major peak, which occurred during the middle of the stadium, coincided with the time of decline in juvenile hormone activity and maximal weight gain. Juvenile hormone esterase activity was generally higher in females than in males. In pupae, one peak of juvenile hormone esterase activity was observed 3 days after pupation in both sexes; activity was again higher in females. Studies on juvenile hormone esterase inhibition using OTFP revealed similar I 50 values for all peaks.