Obligate annual and successive facultative diapause establish a bet-hedging strategy of Rhagoletis cerasi (Diptera: Tephritidae) in seasonally unpredictable environments

摘要

To cope with temporal and spatial heterogeneity of habitats, herbivorous insects in the temperate zone usually enter diapause that facilitates synchronization of their life cycle with specific stages of host plants, such as fruit ripening. In the present study, we address those factors regulating dormancy responses as part of a 'longer strategy' to persist and thrive in temperate environments, focusing on Rhagoletis cerasi, a univoltine, oligophagous species, which overwinters as pupae and emerges when host fruits are available for oviposition at local scale. To ensure population survival and reproduction at habitats with ecological heterogeneity, R. cerasi has evolved a sophisticated diapause strategy based on a combination of local adaptation and diversified bet-hedging strategies. Diapause duration is determined both by (i) the adaptive response to local host fruit phenology patterns (annual diapause) and (ii) the plastic responses to unpredictable inter-annual (temporal) climatic variability that drives a proportion of the populations to extend dormancy by entering a second, successive, facultative cycle of prolonged diapause as part of a bet-hedging strategy. Besides the dormant periods, post-diapause development (which varies among populations) exerts 'fine tune' adjustments that assure synchronization and may correct possible errors. Adults emerging from pupae with prolonged diapause are larger in body size compared with counterparts emerging during the first year of diapause. However, female fecundity rates are reduced, followed by an extended post-oviposition period, whereas adult longevity remains unaffected. Overall, it appears that R. cerasi populations are adapted to ecological conditions of local habitats and respond plastically to unpredictable environmental (climatic) conditions.