Fig. 4.

In vitro release of ecdysteroids (means ± s.e.) by prothoracic glands from P. includens fifth instars. Each pair of prothoracic glands was collected by dissecting cohorts of larvae from 2 to 84 h of the fifth instar. Basal secretion was determined for one prothoracic gland from a given larva by incubating in Grace's medium only for 3 h, while stimulated secretion was determined for the other prothoracic gland by incubating in Grace's medium plus 10 mmol l^–1 dbcAMP for 3 h. A minimum of seven gland pairs were bioassayed per time point. Asterisk indicates a significant difference between the basal and stimulated treatment for a given time point (paired t-test, P≤0.05).