Esterase Changes during the Activation of Pupal Brains of the Saturniid Moth, Hyalophora cecropia

Abstract

THE traditional method of determining whether an endocrine gland in an insect is active or inactive is to see whether it produces a hormonal effect when it is transplanted into a suitable test insect. An alternative is to inject the insect with some labelled compound in order to detect differences between the metabolism of the active and inactive glands¹. The work described in the present communication uses a third method: comparing zymograms of active and inactive endocrine glands. The endocrine organ used was the brain of the cecropia silkworm. Insect brains secrete an agent called “brain hormone” which activates the prothoracic glands and causes the insect to moult. In the cecropia silkworm the brain ceases to secrete this prothoracotrophic hormone immediately after pupation, and the pupa enters diapause. The brain can be re-activated by exposing the pupa to temperatures between 5° C and 10° C for two or more months. Within a few days after they are returned to room temperature the brains of such previously chilled pupae start to secrete brain hormone; the prothoracic glands become activated; and diapause is terminated by the initiation of adult development². This communication describes esterase differences between the zymograms of inactive and active brains.