AbstractThe transcripts of sericin‐type genesMG1andMG2accumulate inGalleria mellonellasilk glands during feeding and decline during molting. ThreeMG1(1.9, 3.2, and 4.2 kb) and twoMG2(dominant 3.4 kb and minor 5.2 kb) transcripts are detectable from the penultimate instar until the end of cocoon spinning. Experiments with isolated larval abdomens showed that the dramatic change in the ratio of 1.9 and 4.2 kbMG1transcripts in the last larval instar is due to lack of JH. Transient rise of ecdysteroid titre in the wandering larvae (day 5 of the last instar) is associated with appearance of additionalMG1transcripts (10.0, 7.2, and 5.0 kb), while the molt‐inducing ecdysteroid surge on day 7 causes a drop of all transcripts. The drop is prevented and the profile of transcripts is reverted to a larval‐like pattern when the last instar larvae are treated with a juvenoid. The profile ofMG1transcripts is affected only when the treatment is applied prior to the start of cocoon spinning (day 6), whereas the decline of the 3.4 kbMG2transcript is averted with applications up to day 7. Presented results are interpreted as showing that JH causes a “status quo” effect by preventing the disappearance of certain transcripts during molting, exerts a “juvenilizing” effect by restoring the larval pattern of splicing, and affects developmental “programming,” presumably by affecting the future pattern of gene expression. © 19