Insect Diapause

Insect diapause is an amazing topic in biology linking together natural history, physiology, ecology, genetics, biochemistry, behaviour and other areas. As a consequence, the literature on insect diapause is enormous. Hundreds of early experimental works published during the first half of the 20th century were reviewed in the 1950s–1960s by A.D. Lees (The Physiology of Diapause in Arthropods. Cambridge: Cambridge University Press, 1955), A.S. Danilevskii (Photoperiodism and Seasonal Development of Insects; first published in Russian in the USSR in 1961, translated and published in English and Japanese, both in 1965), and S.D. Beck (Insect Photoperiodism. New York: Academic Press, 1968). These three pioneering books greatly stimulated further active development of physiology, ecology, and somewhat later – genetics and biochemistry of diapause in insects and arthropods in general in very different parts of the world, and as a result, a new burst of interesting publications on the subject. New methods and techniques were developed to study winter and summer diapauses as well as other very unusual cases of dormancy in laboratory and in the field, new theoretical approaches were suggested to explain deep physiological processes and diversity of realised seasonal adaptations. Publication of thousands of new papers required a new comprehension, and in the 1970s–1980s, three other very important monographs were published by D.S. Saunders (Insect Clocks. Oxford: Pergamon Press, 1976), M.J. Tauber, C.A. Tauber and S. Masaki (Seasonal Adaptations of Insects. Oxford: Oxford University Press, 1986), and H.V. Danks (Insect Dormancy: An Ecological Perspective. Ottawa: Biological Survey of Canada, 1987). Since then, at least 25 years of active research in different (sub)areas of insect diapause have passed, new thousands of papers, chapters, dissertation and reviews have been published, and there was an impression that it became simply impossible to write an up-to-date monographic review which would comprehensively cover what we know about the phenomenon of insect diapause. However, David L. Denlinger successfully managed to do so in his recently published book entitled Insect Diapause (Cambridge: Cambridge University Press, 2022). This book does not review again what has been reviewed in the above mentioned excellent earlier monographs, but rather focuses on what was discovered and published recently.

David L. Denlinger is one of the world’s leading experts on insect diapause. He is a Distinguished University Professor and Professor Emeritus of Entomology at The Ohio State University (USA). He is also a member of the National Academy of Sciences, a Fellow of the Entomological Society of America, and an Honorary Fellow of the Royal Entomological Society. Professor Denlinger’s research now focuses primarily on the molecular mechanisms involved in overwintering of insects. For decades, he used flesh flies as main experimental insects, and readers can see this in the book as many topics are illustrated first of all with the examples from flies’ life and dormancy. It does not mean, however, that the book is biased; in each chapter or section you will find dozens of examples from different arthropods’ taxa.

The book consists of 12 chapters.

The opening Chapters 1 and 2 introduce the main terms and concepts (seasonality of environmental conditions on the planet, etc.). Readers will ascertain the difference between diapause and quiescence, see diapause as a process consisting of different phases, and discover at which stages different species of insect can enter diapause. Winter and summer diapauses, in tropics and high latitudes, special features of diapause in social insects – all these exciting topics are briefly covered in these chapters.

Chapter 3 focuses on variation in the diapause responses within and among populations as well as cases of repeated and prolonged diapauses; it also touches on the issue of how diapause should be considered in insect pest management.

Chapter 4 discusses the cost of diapause and existing diapause alternatives. To diapause is costly, and diapause may influence further development and performance of an organism or a population. But death is not the only alternative!

Chapter 5 deals with interpretations of seasonal cues for programming the diapause entry. Readers are provided with the basics about daylength and photoperiod, spectral characteristics of the signal, how insects monitor changes in daylength, receive the cues, count cycles, what are the roles of brain and pigments. This chapter further introduces several major models of circadian rhythmicity and outlines the roles of temperature, host, and moisture in the process of diapause induction. This is one of the biggest and most complicated chapters in the book, even though the author’s style is clear and understandable.

Chapter 6 describes how insects prepare for diapause. They not only acquire energy resources but also can (well, some of them) prolong or accelerate the pre-diapause stage, migrate (locally or over considerable distances), choose appropriate microhabitats, change colour, form aggregations, switch to wingless morph, or do other amazing things called seasonal adaptations.

Chapter 7 overviews the diapause state itself. Is it really an arrest of development, depression, or a slow process? How can we monitor internal changes? What is going on inside? How are resources (including water) consumed? How is diapause linked to cold hardiness? Many important and complex questions for one chapter. But we are in the middle of the book, thus well prepared.

Chapter 8 dials with the ending of diapause and reinitiation of development. It is a big mistake to think that all troubles linked with overwintering are over, as post-diapause insects may suffer pronounced mortality in spring. Denlinger discusses diapause development, duration of diapause, timing of diapause completion, post-diapause quiescence, importance of synchronisation, etc.

Chapter 9 takes a step back to the beginning and goes deeply into molecular signalling pathways involved in the regulation of diapause and outlines hormones which insects use to control the processes. This is another chapter that might require some basic knowledge from the readers.

Chapter 10 focuses on the genetic control of diapause, selection experiments and patterns of inheritance.

Quite logically, genetics leads to the evolution of diapause, which is discussed in the Chapter 11. What is the origin of diapause? Did it evolve once or numerous times? This chapter also explores responses of insects to latitudinal clines and climate change, as well as analysing links between diapause and evolution of sociality in insects.

The final Chapter 12 provides an overview of wider implications, such as population modelling, pest management, diapause disruption (including chemical and genetic manipulations), development of biological control options, breeding of domesticated species (including ones as feed and food), insect conservation, disease transmission, research on aging, obesity, and development of pharmacology.

There follow 99 pages of approximately 2,000 references, most of which were published after the releases of previous monographs. The book also has convenient Species and Subject Indexes, and a set of 10 colour figures (in total, there are more than 70 black-and-white figures in the book).

At the end of a book review, I am supposed to write something critical. And this is a problem. I did notice a few minor typos, but they are not even big enough to mention. I do not see any serious flaws in the book. Just maybe a wish. Now the book is available as a hard copy or simple pdf files online (in full or as separate chapters) on the website of the publisher. For some readers it might be more useful and comfortable to have a more modern pdf file – with smart navigation, colour figures, active links to at least Indexes and the reference list inside the book (or maybe even to online versions of the cited papers), and a possibility to add readers’ notes.

In general, Insect Diapause is a long awaited and excellent new monograph summarising basics and recent achievements of what we know about such a fascinating phenomenon as insect diapause. A must-read.