Occurrence of free ecdysteroids and yolk protein ecdysteroid conjugates in the embryo of the melon fly, Dacus cucurbitae Coquillet

Date
1990
Authors
Sanders, Deborra A.
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Abstract
The titer of ecdysteroids occurring in the embryos of the melon fly, Dacus cucurbitae Coquillet was determined at each developmental hour by radioimmunoassay. Free ecdysteroids were extracted from eggs in 60% methanol which showed one single peak at 18 h (i.e., time of germ band shortening). The maximal concentration of free ecdysteroids was 81 pg of 20 hydroxyecdysone equivalents per g. No observed morphological changes occurred during the 3 to 4 h peak hormone concentration. The involution of the head and the beginning of the dorsal closure of the midgut were observed during the declining concentration of free ecdysteroids. Embryonic cuticle was secreted ca. 5 to 6 h after the peak concentration of hormone. The major yolk protein (vitellin) was isolated and digested with several proteases to release ecdysteroid conjugates. The extracted conjugates became more immunopositive when hydrolyzed with Helix enzymes. Low amounts of ecdysteroid conjugates were detected in newly oviposited and young embryos. During late embryogenesis, ca. 18 h after oviposition, three peaks of ecdysteroid conjugates were detected. At 19 h, the first maximal concentration of 20 hydroxyecdysone equivalents was 85±1.7 pg/g vitellin. The second and third peaks occurred at 22 and 26 h with maximal concentrations of 20 hydroxyecdysone equivalents 106.5±1.7 and 102±2.3 pg/g vitellin, respectively. The vitellin of the melon fly was composed of two polypeptides, having a molecular weight of 48,000 and 52,000 and an isoelectric point of 6.3.
Description
Typescript.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1990.
Includes bibliographical references (leaves 68-72)
Microfiche.
ix, 73 leaves, bound col. ill. 29 cm
Keywords
Melon fly
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