Dedicated issue: photoperiodic induction of diapause and seasonal morphs

Abstract

Whether transitions from warm to cold in temperate regions or dry to wet in areas nearer the equator, the changing of the seasons is a major stress for most organisms and as such, a major organizer of organismal lifecycles. To mitigate stressful periods and to exploit periods with high resource availability that are favorable for growth and development, insects and other arthropods have evolved a suite of seasonal adaptations including programmed seasonal dormancy, diapause. Yet, climate change, urbanization, and other alterations in land use are increasingly exposing insects and other organisms to changes in seasonality, especially decreased winter cold periods, lengthened growing seasons, and increased climatic variability on the seasonal shoulders in the fall and spring where warm and cold spells are frequently interspersed. Furthermore, increasing globalization has led to many insects expanding into new areas with very different patterns of seasonality than in their home ranges, whether due to inadvertent introductions of invasive species or managed introductions of beneficial pollinators or natural enemies. We must continue to expand our understanding of insect seasonal responses to meet these increasing challenges in seasonal adaption in our ever-changing world. Building greater understanding of the seasonal responses of both pest and beneficial insects will require an inherently interdisciplinary approach that includes a range of expertise from studying organismal behavior and field ecology to identifying the genetic architecture and regulatory physiology of diapause. A recent symposium at the XXV International Congress of Entomology held in Orlando, Florida, USA from 25–30 September 2016 titled ‘Photoperiodic Induction of Diapause and Seasonal Morphs’ provided the forum for such a broad and interdisciplinary discussion. Many symposium participants and several additional investigators generously agreed to contribute papers to this Dedicated Issue of Physiological Entomology. Reflective of the breadth in approaches and perspectives within the sub-field of insect seasonal biology, this issue contains a range of article types. One particularly broad article leverages the rapidly accumulating transcriptomic datasets available for a wide variety of insects and performs a meta-analysis to test the degree to which a common ‘genetic toolkit’ underlies insect diapause responses. Another article reviews the classic literature on diapause in spider mites and puts forth a modern perspective on the genetics of spider mite reproductive diapause with a focus on the essential role of carotenoid compounds. Several more primary data articles follow that range in their approach and perspectives from whole-brain transcriptomics, to focused transcript abundance work on clock genes and photoperiodic responses, and even classical genetic architecture of diapause inheritance patterns. Additional articles cover a gamut of topics from evolutionary ecology of bet-hedging strategies in diapause length and the timing of diapause termination to endocrine changes associated with progression through diapause development, again reflecting the integrative nature of studying insect photoperiodism and seasonal responses. We thank all of our contributors for their timely submissions and efforts that have made it possible to continue the long tradition of both symposia on photoperiodism and seasonal biology at the International Congress of Entomology and producing a published series of papers allied with that session. We expect that this issue will serve to stimulate discussion of past, contemporary, and future issues in the study of insect seasonal biology for both specialist practitioners within the field and among insect biologists in general.