Effects of photoperiod and relative humidity on diapause termination and post-winter development of Rhagoletis cerasi pupae.

Cleopatra A Moraiti,Kirsten Köppler,Nikos T Papadopoulos,Heidrun Vogt

doi:10.1017/s0007485320000073

Abstract

The European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), is a univoltine species that undergoes obligatory summer-winter diapause at pupal stage in the soil (2-5 cm) beneath host trees. To study the effects of photoperiod and relative humidity on diapause termination and post-winter developmental duration of R. cerasi, pupae collected from Dossenheim (Germany) were exposed to different photoperiod or relative humidity regimes during a chilling period ranging from 2 to 8.5 months. Specifically, pupae were exposed to four photoperiod regimes: (a) light conditions (24L:00D), (b) dark conditions (00L:24D), (c) short photoperiod (08L:16D) and (d) long photoperiod (16L:08D), as well as to three relative humidity regimes: (a) low (40% RH), (b) medium (60% RH) and (c) high (70-80% RH). Data revealed that relative humidity is not a significant predictor of diapause termination, but it affects the post-winter developmental period. Higher relative humidity promotes post-winter pupae development. On the other hand, photoperiod significantly affected both diapause termination and post-winter development of R. cerasi pupae. Light conditions (24L:00D) accelerate adult emergence, particularly for females. Regardless of the photoperiod (24L:00D, 00L:24D, 08L:16D), rates of adult emergence were high (>75%) for chilling intervals longer than 6.5 months. Nonetheless, exposure to a long day photoperiod (16L:08D), during chilling, dramatically reduced the proportion of adult emergence following 6 months exposure to chilling. Our findings broaden the understanding of factors regulating diapause responses in European cherry fruit fly, local adaptation and synchronization of adult emergence with the ripening period of major hosts.

Highlights

Diapause is one of the primary mechanisms whereby herbivorous insects synchronize their life cycles with specific phases of host plants (Tauber et al, 1986; Denlinger, 2002)
We investigated the effects of relative humidity and photoperiod on both diapause termination and post-diapause development of R. cerasi pupae that were exposed to various chilling regimes until adult emergence
Taking into account that R. cerasi pupae overwinter underneath host plants in a soil depth ranged usually from 2 to 5 cm based on soil type (Daniel and Grunder, 2012) and that adult emergence is reduced in extremely wet environments and/or wet clay soils (Boller, 1966), we examined the hypothesis that relative humidity but not photoperiod is a significant predictor of both diapause termination and post-diapause developmental duration of R. cerasi pupae

Summary

Introduction

Diapause is one of the primary mechanisms whereby herbivorous insects synchronize their life cycles with specific phases of host plants (Tauber et al, 1986; Denlinger, 2002). Photoperiodism (e.g. exposure to short days of autumn) is most commonly reported in diapause induction and maintenance (Tauber et al, 1986; Masaki, 1999). For the insects of the temperate zone, exposure to low temperatures (0–10°C) is typically a prerequisite for diapause termination (Saulich and Musolin, 2012). High temperatures accelerate post-diapause developmental rates and promote synchronization of adult emergence (Stålhandske et al, 2015; Moraiti et al, 2017). Populations from ecologically different habitats have shown differential responses to environmental factors ( temperature and photoperiod) for terminating diapause and/or concluding post-diapause development (Moraiti et al, 2014, 2017; Stålhandske et al, 2014)

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Conclusion