AbstractJuvenile hormone (JH) biosynthesis by corpora allata (CA) from embryos of the cockroachDiploptera punctatawas measured at four stages during the latter half of embryogenesis. Individual glands from 32‐day‐old embryos that had completed 49% of embryonic development synthesized 0.3 pmol JH III h−1. By day 46 (70% development) gland activity rose to 1.1 pmol JH h−1, but on subsequent days JH synthetic rates declined, measuring only 0.8 pmol h−1on day 56 (86% development) and 0.5 pmol h−1on day 60 (92% development). Differences in JH biosynthesis by CA from different‐aged embryos were more evident when gland activity was corrected for either corpus allatum cell number, which increased progressively from fewer than 200 cells per gland on day 32 to almost 700 cells per gland on day 60, or embryo mass, which increased from 1.6 mg per embryo on day 32 to 10.8 mg per embryo on day 60. JH biosynthetic rates were significantly inhibited in a medium containing 10−8M Dip‐allatostatin 7 which suppressed CA activity by 68, 83, 76, and 51% on days 32, 46, 56, and 60, respectively. In all embryonic stages JH production was significantly stimulated by incubation of glands with 200 μM farnesol, a late precursor in the JH biosynthetic pathway. © 1