The effect of a synthetic precocene on juvenile hormone III titre in late Locusta eggs

Abstract Employing gas chromatography-mass spectrometry with selected-ion monitoring for detection and quantification of juvenile hormones we have measured juvenile hormone titres in late eggs and in hatchlings of Locusta migratoria migratorioides . We also investigated the effect of topical treatment of eggs with 7-ethoxy-precocene II (= precocene III) on subsequent juvenile hormone titres. Only juvenile hormone III was found in eggs or in hatchlings. Substantial amounts of this hormone were present on day 8 after oviposition (embryonic stages XX–XX 1 2 , 66 ± 6% of the whole duration of egg development) by which time the corpora allata of the embryo are well developed. By day 10 after oviposition (embryonic stages XXI–XXII, 82 ± 6% of the whole development) juvenile hormone III titre had markedly increased in normal eggs, but had sharply declined in eggs which had been treated at day 8 with precocene III. Juvenile hormone titres were low in 0–26 h old hatchlings (13 days after oviposition) regardless of whether or not they had been treated with precocene III at day 8. The results show that late embryos are well equipped with some mechanism(s) for metabolic degradation of juvenile hormone III. Normal development from late embryonic stages up to early 2nd-instar hoppers (which occurs even after precocene treatment) is not dependent on the juvenile hormone peak observed in 10-day old eggs. The physiological role of this peak remains to be clarified.