The Antarctic midge, Belgica antarctica, is a unique insect endemic to Antarctica. It has a 2-year life cycle, with larvae overwintering in two different instars and adults emerging the following summer. This seasonality is crucial for adaptation to Antarctica’s harsh climates and ephemeral growing seasons; however, the underlying mechanisms remain unclear. We found that, under summer-like conditions, larvae could develop from egg to the fourth-instar larval stage without interruption, but they never pupated. Spontaneous developmental arrest at this stage suggests that they overwinter in obligate diapause, a genetically determined period of dormancy. The winter cold can terminate this diapause, and long-term cold exposure is more effective. Although this species can utilise two alternative cold tolerance strategies with diapause for overwintering, freezing was more successful than cryoprotective dehydration in allowing survival and developmental resumption in our experimental conditions. In contrast, the first three larval instars continued their development under the same conditions as the fourth-instar larvae. Although we do not exclude the possibility of facultative diapause, they likely overwinter in a quiescent state, an immediate developmental arrest in response to adversity, to maximise exploitation of the short Antarctic summer. Diapause and quiescence ensure developmental and reproductive success in this extremophile insect.

In temperate environments, most species of insects enter an arrested state of development, known as diapause, that enables them to survive the adverse environmental conditions associated with winter. Although diapause is restricted to a single life stage within species of insects, there are examples of insects that overwinter in the egg, larval, pupal, and adult stages. Here we offer a targeted, non-systematic literature review examining how overwintering impacts subsequent reproduction in female insects. Several factors, including the lifestage at which insects overwinter, the type of energy investment strategy females use for breeding, elements of the winter environment, and contributions from male insects can influence trade-offs that female insects face between overwintering survival and post-diapause reproduction. Additionally, climate change and elements of the urban environment, including light pollution and higher temperatures in cities, can exacerbate or ameliorate trade-offs faced by reproducing female insects. Better understanding the trade-offs between overwintering survival and reproduction in insects not only enhances our understanding of the underlying physiological mechanisms and ecological processes governing diapause and reproduction, but also provides opportunities to better manage insect pests and/or support beneficial insects.

Diapause, a stage-specific developmental arrest, is widely exploited by insects to bridge unfavorable seasons. Considerable progress has been made in understanding the ecology, physiology and evolutionary implications of insect diapause, yet intriguing questions remain. A more complete understanding of diapause processes on Earth requires a better geographic spread of investigations, including more work in the tropics and at high latitudes. Questions surrounding energy management and trade-offs between diapause and non-diapause remain understudied. We know little about how maternal effects direct the diapause response, and regulators of prolonged diapause are also poorly understood. Numerous factors that were recently linked to diapause are still waiting to be placed in the regulatory network leading from photoreception to engagement of the diapause program. These factors include epigenetic processes and small noncoding RNAs, and emerging data also suggest a role for the microbiome in diapause regulation. Another intriguing feature of diapause is the complexity of the response, resulting in a diverse suite of responses that comprise the diapause syndrome. Select transcription factors likely serve as master switches turning on these diverse responses, but we are far from understanding the full complexity. The richness of species displaying diapause offers a platform for seeking common components of a 'diapause toolbox'. Across latitudes, during invasion events and in a changing climate, diapause offers grand opportunities to probe evolutionary change and speciation. At a practical level, diapause responses can be manipulated for insect control and long-term storage. Diapausing insects also contain a treasure trove of pharmacological compounds and offer promising models for human health.

Climate change is leading to substantial global thermal changes, which are particularly pronounced in polar regions. Therefore, it is important to examine the impact of heat stress on the reproduction of polar terrestrial arthropods, specifically, how brief extreme events may alter survival. We observed that sublethal heat stress reduces male fecundity in an Antarctic mite, yielding females that produced fewer viable eggs. Females and males collected from microhabitats with high temperatures showed a similar reduction in fertility. This impact is temporary, as indicated by recovery of male fecundity following return to cooler, stable conditions. The diminished fecundity is likely due to a drastic reduction in the expression of male-associated factors that occur in tandem with a substantial increase in the expression of heat shock proteins. Cross-mating between mites from different sites confirmed that heat-exposed populations have impaired male fertility. However, the negative impacts are transient as the effect on fertility declines with recovery time under less stressful conditions. Modeling indicated that heat stress is likely to reduce population growth and that short bouts of non-lethal heat stress could have substantial reproductive effects on local populations of Antarctic arthropods.

Changes in climate and environment can impact the sustainability of populations and biodiversity. Under-standing population genetic diversity in the past and present can help us better predict species' responses to future environmental change. Antarctica has experienced drastic environmental change which threatens its biodiversity. In this study, we characterized the phylogeography and population genetic structure of Belgica antarctica, a wingless midge that is endemic to the western Antarctic Peninsula. This insect has adaptive features to withstand extremes in temperature, salinity, humidity, anoxia and pH. Belgica antarctica is widespread on widely dispersed islands of ice-free habitat, but questions remain regarding its genetic history, diversity and gene flow. We created nuclear-based, single nucleotide polymorphism (SNP) markers and genotyped 229 individuals from 11 populations to examine historical and current population genetic patterns. Our results support recent divergence among populations on different islands within the last 1 Mya. Furthermore, despite a lack of wings, B. antarctica exhibited frequent migration among islands, perhaps via ocean currents or phoresy with Antarctic vertebrates (e.g. seabirds). The close link between the evolutionary history of B. antarctica and the region's environment and ecology emphasize the importance of understanding its population dynamics to predict its persistence under environmental change.

Previous articleNext article No AccessAnatomy, Physiology, and DevelopmentAdvances in Insect Physiology. Volume 63. Edited by Russell Jurenka. Academic Press. Amsterdam (The Netherlands) and New York: Elsevier. $141.10. vii + 229 p.; ill.; no index. ISBN: 9780323952644. 2022.David L. DenlingerDavid L. DenlingerEntomology and Evolution, Ecology & Organismal Biology, Ohio State University, Columbus, Ohio Search for more articles by this author PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmailPrint SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 98, Number 3September 2023 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/726488 For permission to reuse, please contact [email protected].PDF download Crossref reports no articles citing this article.

Our highly seasonal world imposes environmental challenges for insects. To survive these inimical periods they rely on a diapause (dormancy) mechanism to bridge unfavorable seasons. The origin of the term “diapause” is discussed, as well as its relationship to related forms of dormancy in other animals. Diapause is distinct from quiescence in that it is not an immediate response to an adverse environment but is programmed at an earlier developmental stage, an attribute that enables the insect to take steps in preparation for entering the arrested state. Diapause can occur at any point in the life cycle (embryo, larva, pupa, adult), but when it occurs it is species-specific. The chapter summarizes who does it and in what stage, as well as addressing the occurrence of diapause in social insects. The pervasive impact of diapause on the insect life cycle begins prior to diapause and continues well beyond its termination.

The rich diversity of information focusing on pupal diapause in the sarcophagids makes this fly family among the bestunderstood diapause models. This review summarizes the occurrence of pupal diapause in fl esh fl ies from broad geographic regions of the world, as well as the apparent absence of diapause in select regions. The environmental cues used for programming diapause are discussed, as well as the requirements for breaking diapause. This taxon has been used for experiments ranging from the ecological to the molecular and offers a comprehensive overview of the diapause phenotype. A wide range of diapause attributes defi ne the diapause phenotype of fl esh fl ies, offering insights into such features as clock mechanisms, signaling pathwater balance, and other attributes, generating a diapause profi le that offers an attractive comparison for diapause in other insect species as well as with other forms of animal dormancy.

Diverse physiological features characterize the diapause state. Development is halted or dramatically retarded, the cell cycle is arrested, metabolic rates are suppressed, and a global metabolic shift from aerobic to anaerobic metabolism is evident. Energy reserves and body water are usually not replenished during diapause, thus conservation of these resources is essential. Patterns of heartbeat and discontinuous gas exchange are distinct during diapause. Structural modifications such as flight muscle degeneration in adults and cytoskeletal distinctions are evident at both tissue and transcriptomic levels. Defense responses are usually bolstered. Heat shock proteins are commonly upregulated, as are immune and antioxidant responses, as well as cold-hardening mechanisms and hypoxia responses essential for surviving in winter habitats that are oxygen-limited. Diapause is not static, as evidenced by systematic shifts in metabolism and energy sources tapped at different phases of diapause, as well as changes in responsiveness to exogenous hormones or environmental stress.

Tools that could be used to subvert the insect diapause response offer potential for insect pest management as well as for the experimental manipulation of insects and the facilitation of mass rearing procedures. In some cases, it is desirable to break diapause on demand and in other cases, it may be attractive to exploit diapause for long-term storage of biocontrol agents or valuable experimental lines. This review highlights some of the diapause disruptors reported in the literature, as well as chemical and physical manipulations that can be used to extend diapause or even induce diapause in an insect not programmed for diapause. The insect hormones are quite effective agents for breaking diapause and in some cases for extending the duration of diapause, but a collection of other chemical agents can also act as potent diapause disruptors, e.g. organic solvents, weak acids and bases, carbon dioxide, imidazole compounds, LSD, deuterium oxide, DMSO, ouabain, cholera toxin, cyclic GMP, heavy metals, and hydrogen peroxide. Physical manipulations such as artificial light at night, anoxia, shaking and heat shock are also known diapause disruptors. Some of these documented manipulations prevent diapause, others terminate diapause immediately, others alter the duration of diapause, and a few compounds can induce a diapause-like state in insects that are not programmed for diapause. The diversity of tools noted in the literature offers promise for the development of new tools or manipulations that possibly could be used to disrupt diapause or manage diapause in controlled laboratory experiments and in mass-rearing facilities.

Diapause offers the obvious benefit of enabling an insect to survive seasons that would otherwise be unsuitable for continuous development, but it usually comes at a cost. Costs may be reflected during the insect’s life or as reduced fitness in the progeny. Costs can include high mortality, depletion of energy reserves, low fecundity, delay in oviposition, shortened post-diapause longevity, and missed opportunities as a consequence of lost generations. Costs may differ between males and females, resulting in sex-specific trade-offs that may influence the timing of diapause entry. A few species, however, appear to have escaped obvious costs associated with diapause. Alternatives enable some insects to survive without diapause. These include entering quiescence (a dormant state readily entered and exited in direct response to prevailing conditions), cold hardening without diapause, extending the life cycle without diapause, seeking a favorable environment, and remaining winter-active.