Prolonged pupal dormancy is associated with significant fitness cost for adults of Rhagoletis cerasi (Diptera: Tephritidae)

In temperate areas, dormancy (diapause and/or quiescence) enables herbivorous insect species to persist and thrive by synchronizing growth and reproduction with the seasonal phenology of their host plants. Within-population variability in dormancy increases survival chances under unpredictable environmental changes. However, prolonged dormancy may be costly, incurring trade-offs in important adult fitness traits such as life span and reproduction. We used the European cherry fruit fly, Rhagoletis cerasi, a stenophagous, univoltine species that overwinters in the pupal stage for usually one or more years to test the hypotheses that prolonged dormancy of pupae has trade-offs with body size, survival and reproduction of the resulting adults. We used two geographically isolated populations of R. cerasi to compare the demographic traits of adults obtained from pupae subjected to one or two cycles of warm-cold periods (annual and prolonged dormancy respectively). Regardless of population, adults from pupae that experienced prolonged dormancy were larger than counterparts emerging within 1year. Prolonged dormancy did not affect adult longevity but both lifetime fecundity and oviposition were significantly decreased. Extension of the life cycle of some individuals in R. cerasi populations in association with prolonged dormancy is likely a bet-hedging strategy.     

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

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.     

Diapause termination of Rhagoletis cerasi pupae is regulated by local adaptation and phenotypic plasticity: escape in time through bet‐hedging strategies

Persistence and thriving of univoltine, herbivore insect species of the temperate zone rely on obligate diapause response that ensures winter survival and synchronization with host phenology. We used a stenophagous fruit fly (Rhagoletis cerasi) with obligate pupae diapause to determine genetic and environmental effects on diapause intensity of geographically isolated populations with habitat heterogeneity. Pupae from two Greek and one German populations with various gene flow rates were exposed at five constant chilling temperatures (0–12 °C) for different durations and then incubated at a high temperature until all adults have emerged. Pupae diapause intensity differs among Greek and German populations, suggesting an adaptive response to habitat heterogeneity (mostly differences in phenology patterns of local host cultivars). Moderately warm winter temperatures, such as 8 °C, promote diapause termination in all three populations. Insufficient chilling (short duration or warmer temperatures) regulates the expression of prolonged dormancy. Interestingly, extended chilling (longer than required for terminating diapause) ‘return’ pupae to another (facultative) cycle of dormancy enabling adults to emerge during the next appropriate ‘window of time’; a strategy first time reported for univoltine insects. Consequently, diapause duration of R. cerasi is determined both by i) the adaptive response to local climatic conditions (annual dormancy) and ii) the plastic responses to interannual climatic variability resulting in two types of long life cycles within populations, prolonged and facultative dormancy as response to insufficient chilling and extended exposure to chilling, respectively. Long life cycles are expressed as a part of dormancy bet‐hedging strategies of R. cerasi populations.     

New aspects in investigations of diapause and non-diapause dormancy types in insects and other arthropods

The paper resumes consideration of the problem posed by the Russian ecologist A.M. Emme (1953) on the need for a comparative study of diapause and quiescence (a non-diapause type of dormancy) in insects and other arthropods. The problem has recently become important due to the scarcity of eco-physiological studies of non-diapause dormancy, whose role in life cycle regulation remains unclear, and to the fact that most attention is now paid to diapause (as the leading adaptation in the control of seasonal development of arthropods). Analysis of data available for insects and acariform mites revealed the prospects of a comprehensive study of non-diapause forms of dormancy known presently (the common stage-independent quiescence, modified stage-specific quiescence, and post-diapause quiescence). The combination of post-diapause quiescence and diapause proper, revealed in many recent insects and acariform mites (mainly Prostigmata), may correspond to the initial ancestral state of dormancy in arthropods, representing a universal adaptation to both predictable and unpredictable environmental changes. This hypothesis gives a reasonable explanation of the possible dual nature of winter dormancy in oribatid mites (in contrast to the existing contradictory interpretations of their hibernal dormancy as only quiescence or only diapause).     

Extended life cycle in the chestnut weevil: prolonged or repeated diapause?

Many insect species extend the life cycle of a part of their population over several years. The adaptive value of these long cycles is now well documented, but the physiological processes underlying them have been little studied. Long life cycles are usually viewed as resulting from prolonged diapause proceeding from a simple extension of the usual winter diapause. However, this hypothesis has not been greatly tested, and information is lacking for species with a larval diapause. The energetic cost of a prolonged larval diapause also needs to be measured, because the few published estimates of lipid consumption concern an imaginal diapause. It is not therefore clear whether the negligible lipid consumption observed during adult prolonged diapause can be extrapolated to larval diapause. From microrespirometry and lipid measures in the chestnut weevil, Curculio elephas Gyllenhal (Coleoptera: Curculionidae), we show that: (1) in contrast to the usual hypothesis, the long cycle does not result from an extension of larval winter diapause, but is due to a prolonged diapause occurring secondarily to a developmental phase, and (2) energy consumption during the prolonged diapause is not negligible, but is provided for by a higher initial lipid content in the long cycle individuals. The adaptive value of the observed cycle is discussed.     

Morphological changes during diapause stages in the embryonic cortex of the annual killifish <Emphasis Type="Italic">Millerichthys robustus</Emphasis> (Cyprinodontiformes: Cynolebiidae) under natural conditions

The annual killifish inhabits in extreme locations with unpredictable rainy season where survives through the massive generation of embryos resistant of drought, capable to remain in a state of metabolic dormancy (three moments of diapause during embryonic development) protected by embryonic cortical structures: perivitelline space, egg envelope and its ornamented structures (trapeze-shaped projections and filaments in Millerichthys robustus). This research describes, for the first time, changes in cortical structures during three diapause stages in embryos of annual fish M. robustus during an annual life cycle. Embryos were collected in three periods through the year in a temporal water body: flood, drought and wet. During flood period all embryos were found in diapause I (during epiboly, dispersion of the blastomeres stage) with maximum thickness in all cortical structures and presence of egg envelope filaments. During drought period all embryos were in diapause II (development during somitogenesis, before the organogenesis) and its structures reduced its thickness significantly and lost the egg envelope filaments. Interestingly, embryos in diapause II and III (embryonic development completed in a pre hatching stage) were found during wet period (an example of bet-hedging strategy) in which all structures presented a recovery tending to its original condition observed during flood period. This research demonstrates that annual fish embryos respond to their exposure to seasonal environmental variations with dynamic structural changes that are fundamental for their survival.     

Prolonged diapause: a trait increasing invasion speed?

Invasive species are considered to be the second cause of biodiversity erosion, and one challenge is to determine the life history traits that cause an increased invasion capacity. Prolonged diapause is a major trait in evolution and insect population dynamics, but its effects on invasion speed remain unknown. From a recently developed mathematical approach (integro-difference equations) applied to the insect dormancy, we show that despite a dispersal cost, bet-hedging diapause strategies with low (0.1-0.2) prolonged diapause frequency (emergence after 1 or 2 years) can have a higher invasion speed than a simple diapause strategy (emergence after 1 year) when the environmental stochasticity is sufficiently high. In such conditions, prolonged diapause is a trait supporting invasion capacity by increasing population stochastic growth rate. This conclusion, which applies to a large range of demographic parameters, is in opposition to the usual view that prolonged dormancy is an alternative strategy to dispersal. However, prolonged diapause does not support invasion if the level of environmental stochasticity is low. Therefore, conclusion about its influence on invasion ability needs a good knowledge of environmental stochasticity in the introduction area of considered species.     

Prolonged diapause and the stability of host-parasitoid interactions

We investigated the effect on host-parasitoid dynamics of prolonged diapause, a feature of the life history of many animals living in unpredictable environments, by modifying the classical May (J. Anim. Ecol. 47 (1978) 833) host-parasitoid model. We considered three patterns of development of host and parasitoid: (a) prolonged parasitoid diapause controlled by host physiology, (b) parasitoid interference in host development, preventing parasitized hosts from prolonging diapause, and (c) host diapause independent of parasitoid attack. We found that single-year prolonged diapause shifted the boundaries of the May model towards a slight increase in stability. Longer periods of diapause prolongation had a stronger influence, but this influence remained modest if we considered realistic parameter values. In contrast to other recent studies, our results suggest that prolonged diapause does not necessarily compensate for the destabilizing effects of time lags on the influence of parasitoids on population dynamics.     

Presence of three diapauses in a subtropical cockroach: control mechanisms and adaptive significance

Abstract.  Diapause is common among insects and is regarded as an adaptive response to periodic occurrence of adverse conditions. It occurs at a particular developmental stage, typically only once in a lifetime. However, little is known about the details of the control mechanism of life cycles with multiple diapauses in insects. In this study, a complex 2-year life cycle with three types of diapause is reported in a subtropical cockroach, Symploce japonica : a winter diapause in mid-nymphal instars, a summer diapause in later nymphal instars, and a reproductive diapause is reported in the adult stage. Nymphal development was extremely slow either at short days (winter diapause) or long days (summer diapause). Nymphs in summer diapause matured rapidly when transferred from long days to short days, indicating that seasonal changes in day-length are the pivotal factor in the control of this life cycle. It is proposed that the main significance of winter diapause in this subtropical species is to enable the nymphs to survive the mild winter successfully with reduced energy demand, and that of summer diapause is to delay adult emergence until late in the autumn for successful induction of the following adult diapause. Adults do not emerge until shortly before winter, yet the presence of diapause in the adult stage does not simply appear to be a response to cope with the winter conditions but, instead, ensures that reproduction will occur early the next year, before summer, because reproduction is greatly hampered at high temperature.     

One phase of the dormancy developmental pathway is critical for the evolution of insect seasonality

Evolutionary change in the timing of dormancy enables animals and plants to adapt to changing seasonal environments and can result in ecological speciation. Despite its clear biological importance, the mechanisms underlying the evolution of dormancy timing in animals remain poorly understood because of a lack of anatomical landmarks to discern which phase of dormancy an individual is experiencing. Taking advantage of the nearly universal characteristic of metabolic suppression during insect dormancy (diapause), we use patterns of respiratory metabolism to document physiological landmarks of dormancy and test which of the distinct phases of the dormancy developmental pathway contribute to a month‐long shift in diapause timing between a pair of incipient moth species. Here, we show that divergence in life cycle between the earlier‐emerging E‐strain and the later‐emerging Z‐strain of European corn borer (ECB) is clearly explained by a delay in the timing of the developmental transition from the diapause maintenance phase to the termination phase. Along with recent findings indicating that life‐cycle differences between ECB strains stem from allelic variation at a single sex‐linked locus, our results demonstrate how dramatic shifts in animal seasonality can result from simple developmental and genetic changes. Although characterizing the multiple phases of the diapause developmental programme in other locally adapted populations and species will undoubtedly yield surprises about the nature of animal dormancy, results in the ECB moth suggest that focusing on genetic variation in the timing of the dormancy termination phase may help explain how (or whether) organisms rapidly respond to global climate change, expand their ranges after accidental or managed introductions, undergo seasonal adaptation, or evolve into distinct species through allochronic isolation.     

Distribution of crustacean diapause: micro- and macroevolutionary pattern and process

Theoretical predictions for the relationships between duration of dormancy, reproductive life span, and dispersal ability developed for plants in temporally varying environments are applied here to crustaceans. Mathematical models suggest that diapause duration should negatively covary with adult life span, and that both diapause and life span should negatively covary with dispersal ability. A survey of 167 crustacean species from 20 orders and three classes confirms that species with prolonged diapause have short adult life spans and those with long adult lives either have diapause lasting less than a year, or do not diapause at all. Prolonged diapause is more common among small or inland water crustaceans than it is among large or marine species, whereas large or marine species have significantly longer adult life spans on average than do those that are small or from inland waters. A greater fraction of species in the Branchiopoda exhibit prolonged diapause than do members of the Maxillopoda which, in turn, are more likely to exhibit prolonged diapause than are the Malacostraca. A greater fraction of malacostracan species have adult life spans exceeding one year than do species in either the Branchiopoda or the Maxillopoda. Cladistic analysis shows that phylogenetic constraint is likely to be at least in part responsible for the expression of diapause among the Crustacea. We conclude that both natural selection and macroevolutionary pattern have influenced the distribution of diapause among modern crustaceans.     

Repeated cycles of chilling and warming effectively terminate prolonged larval diapause in the chestnut weevil, Curculio sikkimensis

Curculio sikkimensis (Coleoptera: Curculionidae) requires one or more years to complete its life cycle, owing to prolonged larval diapause. To compare the effects of temperature cycles and total periods of chilling on the termination of prolonged diapause, larvae were subjected to different chilling (5 degrees C) and warming (20 degrees C) cycles ranging from 30 to 720 days, and all cycles were repeated until the sum of chilling and warming periods reached 720 days. The prolonged diapause of C. sikkimensis was more effectively terminated by repeated cycles of chilling and warming than by prolonging the continuous chilling period. However, extremely short temperature cycles were not highly effective in enhancing diapause termination, even when such cycles were repeated many times. To examine the role of warming periods on diapause termination, diapause larvae were subjected to a sequence of chilling (120 days at 5 degrees C) and warming (240 days at 20 degrees C) with a warming period (0-120 days at 20 degrees C) inserted in the chilling period. Diapause larvae that were not reactivated in the first chilling period required exposure to a certain period of warming before they were able to complete diapause development in the subsequent chilling. Thus, C. sikkimensis appears to spread its reactivation times over several years in response to seasonal temperature cycles.     

Nutritional and photoperiodic control of the seasonal reproductive cycle in Chrysopa mohave (Neuroptera)

Chrysopa mohave adults, which are predaceous, undergo a facultative reproductive diapause which can be induced, averted, and terminated in the laboratory by manipulating either photoperiod or diet. Photoperiods of LD 14:10 or shorter evoke a photoperiodically controlled diapause which breaks in long day (LD 16:8) conditions. Withholding prey induces the diapause syndrome in animals experiencing long day lengths, whereas supplying prey terminates this diapause; thus food constitutes a major factor in diapause induction and termination.Under short day regimens, with prey continuously present, diapause persists for approximately 60 days at 24±1°C; however, protein-fed, short day animals retain the diapause characteristics until they receive prey.Our experimental results in combination with field observations and examination of collected specimens, indicate four periods in the annual reproductive cycle as follows. The animals reproduce during April, May, and June when photoperiods are long and prey abundant. When prey become scarce during the dry months of the California summer, part of the population enters a food mediated diapause. During October, November, and December a short day diapause occurs in the population. Although the photoperiodic maintenance of diapause probably ends during early winter, the insects retain the diapause symptoms until prey becomes abundant at the end of March.     

Adaptation in a variable environment: Phenotypic plasticity and bet‐hedging during egg diapause and hatching in an annual killifish

Two ways in which organisms adapt to variable environments are phenotypic plasticity and bet‐hedging. Theory suggests that bet‐hedging is expected to evolve in unpredictable environments for which reliable cues indicative of future conditions (or season length) are lacking. Alternatively, if reliable cues exist indicating future conditions, organisms will be under selection to produce the most appropriate phenotype —that is, adaptive phenotypic plasticity. Here, we experimentally test which of these modes of adaptation are at play in killifish that have evolved an annual life cycle. These fish persist in ephemeral pools that completely dry each season through the production of eggs that can remain in developmental arrest, or diapause, buried in the soil, until the following rainy season. Consistent with diversified bet‐hedging (a risk spreading strategy), we demonstrate that the eggs of the annual killifish Nothobranchius furzeri exhibit variation at multiple levels—whether or not different stages of diapause are entered, for how long diapause is entered, and the timing of hatching—and this variation persists after controlling for both genetic and environmental sources of variation. However, we show that phenotypic plasticity is also present in that the proportion of eggs that enter diapause is influenced by environmental factors (temperature and light level) that vary seasonally. In nature there is typically a large parameter zone where environmental cues are somewhat correlated with seasonality, but not perfectly so, such that it may be advantageous to have a combination of both bet‐hedging and plasticity.     

How climate change affects the seasonal ecology of insect parasitoids

1. In the context of global change, modifications in winter conditions may disrupt the seasonal phenology patterns of organisms, modify the synchrony of closely interacting species and lead to unpredictable outcomes at different ecological scales. 2. Parasites are present in almost every food web and their interactions with hosts greatly contribute to ecosystem functioning. Among upper trophic levels of terrestrial ecosystems, insect parasitoids are key components in terms of functioning and species richness. Parasitoids respond to climate change in similar ways to other insects, but their close relationship with their hosts and their particular life cycle – alternating between parasitic and free-living forms – make them special cases. 3. This article reviews of the mechanisms likely to undergo plastic or evolutionary adjustments when exposed to climate change that could modify insect seasonal strategies. Different scenarios are then proposed for the evolution of parasitoid insect seasonal ecology by exploring three anticipated outcomes of climate change: (i) decreased severity of winter cold; (ii) decreased winter duration; and (iii) increased extreme seasonal climatic events and environmental stochasticity. 4. The capacities of insects to adapt to new environmental conditions, either through plasticity or genetic evolution, are highlighted. They may reduce diapause expression, adapt to changing cues to initiate or terminate diapause, increase voltinism, or develop overwintering bet-hedging strategies, but parasitoids' responses will be highly constrained by those of their hosts. 5. Changes in the seasonal ecology of parasitoids may have consequences on host–parasitoid synchrony and population cycles, food-web functioning, and ecosystem services such as biological pest control.     

Pre‐wintering conditions and post‐winter performance in a solitary bee: does diapause impose an energetic cost on reproductive success?

1. Diapause is a dynamic process of low metabolic activity that allows insects to survive periods of harsh conditions. Notwithstanding the lowered metabolism, and because diapausing insects have no access to food, diapause has an energetic cost that may affect post‐diapause performance. 2. Previous studies on the solitary bee Osmia lignaria have shown that prolonged pre‐wintering periods (the time during which individuals already in diapause remain at warm temperatures) are associated with elevated lipid consumption, fat body depletion, and body weight loss. The present study investigated whether prolonged pre‐wintering also affects reproduction, i.e. whether the costs associated with diapause could have an effect on post‐diapause performance in this species. 3. Females were exposed to a range of pre‐wintering conditions, and ovary development and individual post‐wintering performance were monitored throughout their adult life span. 4. No evidence of an effect of pre‐wintering duration on post‐diapause reproductive success was found. Expected differences in the timing of establishment were not observed because ovary maturation was, surprisingly, not arrested during pre‐wintering. Prolonged pre‐wintering duration did not result in decreased life span, probably because emerging females could rapidly replenish their metabolic reserves through feeding. However, there was a very strong effect of the duration of the pre‐emergence period on the likelihood of nest establishment. 5. Longevity, the main factor determining fecundity in Osmia, is subjected to high levels of intrinsic variability, even among females of similar size exposed to identical conditions during development and nesting.     

Significance of photoperiodism and diapause control in the multicycle Crustacean Daphnia pulex Leydig

Eukaryote cells traverse the cell cycle, or become growth-arrested at one of two blockpoints, as in an engine of energy conversion. Diapause describes that growth arrest in the cell cycle(s), of single and multicellular individuals. Its temporal position in an annual cycle is an evolved response to the external environment, which is also responsible for sending the necessary signal(s) to receptors in the cell, or to the neural integrator of multicellular individuals.The diapause syndrome, common to protists and Crustacean waterfleas, includes the cell cycle arrest, as well as the induction of mating types, gametogenesis, packaging of the diapaused stage, and the duration of the diapause. The cell-/ life-cycle may be interrupted in a variety of seasonal patterns, which are triggered by one or more identified external signals and are integrated by cell and circadian clocks. Daphnia pulex displays four distinct seasonal patterns of embryonic diapause in four putative genotypes.The ecological implications of diapause in life cycles may be sought in such questions as 1, environmental control of temporal and spatial boundaries in sessile populations; 2, application of knowledge of diapause/dormancy cycles to redesigning ecological communities; and 3, integration of mechanistic and biosystematic approaches in ecology.     

Insect diapause-specific peptide from the leaf beetle has consensus with a putative iridovirus peptide

Diapause and hibernation during periods of environmental adversity are essential features of the life cycle in many organisms, yet the molecular basis for these events differs among animals. We have identified an endogenous diapause/hibernation-specific peptide, from the leaf beetle Gastrophysa atrocyanea. This peptide provides antifungal activity, acts as a N-type voltage-gated Ca2+ channel blocker, and has a new consensus sequence with an unknown polypeptide encoded in the insect iridescent virus. These results indicate that the diapause-specific peptide may be utilized as a probe to analyze and compare functional and evolutional aspects of the life cycles of insects and iridoviruses.     

The evolution of an annual life cycle in killifish: adaptation to ephemeral aquatic environments through embryonic diapause

An annual life cycle is characterized by growth, maturity, and reproduction condensed into a single, short season favourable to development, with production of embryos (seeds, cysts, or eggs) capable of surviving harsh conditions which juveniles or adults cannot tolerate. More typically associated with plants in desert environments, or temperate‐zone insects exposed to freezing winters, the evolution of an annual life cycle in vertebrates is fairly novel. Killifish, small sexually dimorphic fishes in the Order Cyprinodontiformes, have adapted to seasonally ephemeral water bodies across much of Africa and South America through the independent evolution of an annual life history. These annual killifish produce hardy desiccation‐resistant eggs that undergo diapause (developmental arrest) and remain buried in the soil for long periods when fish have perished due to the drying of their habitat. Killifish are found in aquatic habitats that span a continuum from permanent and stable to seasonal and variable, thus providing a useful system in which to piece together the evolutionary history of this life cycle using natural comparative variation. I first review adaptations for life in ephemeral aquatic environments in killifish, with particular emphasis on the evolution of embryonic diapause. I then bring together available evidence from a variety of approaches and provide a scenario for how this annual life cycle evolved. There are a number of features within Aplocheiloidei killifish including their inhabitation of marginal or edge aquatic habitat, their small size and rapid attainment of maturity, and egg properties that make them particularly well suited to the colonization of ephemeral waters.     

Seasonal cycles of noctuid moths of the subfamily Plusiinae (Lepidoptera,Noctuidae) of the Palaearctic: Diversity and environmental control

Analysis of data on seasonal development of noctuid moths of the subfamily Plusiinae shows that the control of their seasonal cycles is poorly understood. At the same time, the available data demonstrate considerable diversity of the seasonal patterns of Plusiinae species from different regions. The homodynamic type of seasonal development has been found in Trichoplusia ni and Ctenoplusia agnata of the tribe Argyrogrammatini and in Autographa gamma of the Plusiini. The seasonal development of these southern noctuids is accompanied by regular interzonal migrations of flying adults. When spreading northwards, they can produce a different number of annual generations, depending on the local climatic conditions, and establish temporary local populations whose longevity is limited by the available thermal resources. Adults of some species may fly back southwards, but it is more likely that individuals from temporary local populations cannot survive long winters and are destined to die. The heterodynamic type of seasonal cycles allows insects to survive in the regions with pronounced seasonality of climate. This type of seasonal development includes univoltine, multivoltine, and semivoltine seasonal cycles. Univoltine seasonal cycles with obligate diapause are known in Autographa buraetica, A. excelsa, and Syngrapha ain (Plusiini). Diapause provides tolerance to both low temperatures and a prolonged period when food is unavailable. In Syngrapha ottolenguii (Plusiini), the same result is achieved by inclusion of two photoperiodically controlled diapauses (winter larval and summer adult ones) into the life cycle. The semivoltine seasonal cycle has been reported in only one species of Plusiinae, namely Syngrapha devergens. Larvae of this moth overwinter twice before pupation. Multivoltinism is common in the tribe Plusiini. Depending on the latitude, different species of this tribe can produce up to four generations per year and overwinter as middle-instar larvae in the state of facultative diapause. However, the characteristics of diapause vary substantially between the species: diapause can be deep and stable (as in Diachrysia chrysitis, Plusiini) or unstable and thus not ensuring successful overwintering and steady population growth (as in Macdunnoughia confusa, Plusiini). The seasonal adaptations known in Plusiinae include migrations, winter and summer diapauses, photoperiodic control of larval growth rates, and seasonal polyphenism of larval body coloration. In general, seasonal adaptations of Plusiinae are determined by local environmental conditions and only loosely associated with the systematic position of particular taxa. Only the tribe Abrostolini stands apart from other taxa of Plusiinae: moths of this tribe differ not only in morphology but also in peculiarities of their seasonal development, because all the species of this tribe overwinter as pupae and their seasonal cycles are therefore different from those of the rest of Plusiinae.