Studies on the moulting hormones of the desert locust schistocerca gregaria

A systematic investigation of extracts of late 5th instar nymphs of the desert locust Schistocerca gregaria has been carried out to detect and isolate moult-inducing substances. Moulting activity was detected by bioassay using the isolated abdomens of 4th instar nymphs as the test objects. At least three substances with moulting activity have been detected in whole locusts, and one has been isolated and identified as the known arthropod moulting hormone, 20-hydroxyecdysone. The other two active substances have been obtained as partially purified extracts. No ecdysone has been detected in any of the locust extracts examined. A gas-liquid 'chromatographic method has been developed for the determination of steroid hormones of the ecdysone type in biological materials. Model steroids were used to establish the conditions for the preparation and gas liquid chomatography of trimethylsilyl-methoxime derivatives of ecdysone and 20-hydroxyecdysone, and derivatives of the ecdysones were identified by mass spectrometry. The gas-liquid chromatography and the mass spectra of derivatives of the model compounds and the ecdysones are discussed. The gas-liquid chromatographic method has been applied to the examination of extracts from whole nymphs and various tissues for 20-hydroxyecdysone. This hormone was first detected and determined in purified extracts from whole locusts by gas-liquid chromatography, and has subsequently been determined in nymphs at daily intervals from day eight of the 4th instar to day three of adult development by this method. The titre was a maximum on the days of ecdysis, a minimum in the middle of the 5th instar, and fell to a low level following the emergence of the adult. Prothoracic glands isolated from late 5th ins tar nymphs have been shown, by bioassay, to contain at least two moult-inducing substances which are similar to the two unidentified active substances from whole nymphs. It is suggested that the two active components from glands are the same as those found in whole locusts, and that they are produced in the prothoracic gland. No 20-hydroxyecdysone was detected in extracts from prothoracic glands, and it is considered unlikely that this hormone is produced in the gland. Blood extracts from 5th instar locusts have been found to contain only a small proportion of the moult-inducing substances present in whole nymphs, and no 20-hydroxyecdysone could be detected. This hormone was also undetected in oenocyte bearing abdominal tissues, but as the proportion of oenocytes in the tissue was very low, this could not be used as a guide to the 20-hydroxyecdysone content of the oenocytes