Abstract
Simple SummaryIn insects, the precise timing of metamorphosis and diapause is regulated by hormones. The Chinese oak silkworm, Antheraea pernyi, is a typical pupal diapause insect. Bivoltine species enter diapause in winter and terminate it under suitable environmental conditions in the following year; they produce 70% of total cocoons, whereas univoltine species in lower-latitude areas enter diapause in summer and contribute just one generation a year. A long photoperiod can trigger termination of pupal diapause. It is not clear how photoperiod influences hormone gene expression. Here, hormone-related genes were cloned, and their expression patterns were studied under different photoperiod treatments. The results will help us to understand the molecular changes during diapause termination under long photoperiods and improve breeding of multi-generation tussah pupae in areas where they are naturally univoltine.The Chinese oak silkworm is commonly used in pupal diapause research. In this study, a long photoperiod was used to trigger pupal diapause termination. Genes encoding three hormones, namely prothoracicotropic hormone (PTTH), ecdysis triggering hormone (ETH), and eclosion hormone (EH), were studied. Additionally, ecdysteroids (mainly 20-hydroxyecdysone, 20E) were quantified by HPLC. Pupal diapause stage was determined by measuring respiratory intensity. The pupae enter a low metabolic rate, which starts approximately 1 month after pupal emergence. ApPTTH expression showed a small increase at 14 days and then a larger increase from 35 days under the long photoperiod treatment. A similar pattern was observed for the titer of 20E in the hemolymph. However, ApETH expression later increased under the long photoperiod treatment (42 days) just before eclosion. Moreover, ApEH expression increased from 21 to 35 days, and then decreased before ecdysis. These results suggest that hormone-related gene expression is closely related to pupal development. Our study lays a foundation for future diapause studies in A. pernyi.
Highlights
Diapause—programmed developmental arrest—helps several insects survive in unfavorable environments
Insects have to adjust their behavior, metabolism, physiology, and developmental course to adapt to day length [2]
Ecdysteroids secreted by the prothoracic glands (PGs) or analogous organs are important for growth, molting, and metamorphosis [4]
Summary
Diapause—programmed developmental arrest—helps several insects survive in unfavorable environments. Insects can enter diapause in various developmental stages, including the egg, larval, pupal, and adult stages. Diapause involves reduced metabolic activity during adverse seasons, and it can occur in response to seasonal changes in both temperature and day length. Insects have to adjust their behavior, metabolism, physiology, and developmental course to adapt to day length [2]. It can regulate energy use and maximize allocation towards growth and reproduction during suitable seasons [3]. PTTH stimulates the PGs to synthesize and release ecdysone. In Drosophila, PTTH plays a central role in controlling the duration of the larval phase. Knockout of PTTH causes several developmental defects [7]. In the cabbage army moth, Mamestra brassicae, PTTH is maintained at high levels in non-diapausing pupae, but it is often undetectable in diapausing pupae [8]
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