A molecular-genetic understanding of diapause in spider mites: current knowledge and future directions

During unfavourable conditions, many arthropods have the ability to enter into diapause and synchronize their development and reproduction to seasonal patterns. Diapause or winter hibernation in insects and mites is set off by a number of cues, with photoperiod being the most well-defined and strongest signal. This review focuses on the current knowledge of '-omics' data and the genetics of diapause in the two-spotted spider mite Tetranychus urticae, a member of the family Tetranychidae (Arthropoda: Chelicerata: Arachnida: Acari). This species is a serious polyphagous pest and females undergo a reproductive facultative diapause when immature stages are exposed to long nights. Winter hibernation induces different physiological processes characterized by a metabolic suppression, different energy use, increased stress tolerance and the production of cryoprotectants, all initiated by a complex signal transduction pathway. Keto-carotenoids are known to cause the deeply orange colour typical for diapausing females. Furthermore, research with colour mutants of T. urticae has shown the need for carotenoids with respect to the induction of diapause, even though the molecular-genetic mechanisms underlying these colour phenotypes are still unknown. In addition, marked latitudinal variation in diapause incidence among populations has been observed in nature, with modes of inheritance ranging from recessive to dominant, as well as monogenic to polygenic. We end by highlighting the emerging opportunities for functional studies that aim to unravel the complex factors underlying diapause in spider mites.