Abstract: Background The interplay between global warming and invasive arthropods in temperate zones is of utmost interest in terms of the potential expansions of vector-borne diseases. Up to now, investigations on the recent establishment of mosquito vectors have focused on temperatures during their phases of activity. However, cold temperatures may also act as a strong ecological constraint. Projected changes in winter climate indicate an increase of mean minimum temperatures of the coldest quarter, less frequent days with frost and a shorter frost-season in Europe at the end of the century. Nevertheless, single cold extremes are also expected to persist under warming scenarios, which have a strong impact on reproduction success.

Abstract: Developmental arrest, a critical component of the life cycle in animals as diverse as nematodes (dauer state), insects (diapause), and vertebrates (hibernation), results in dramatic depression of the metabolic rate and a profound extension in longevity. Although many details of the hormonal systems controlling developmental arrest are well-known, we know little about the interactions between metabolic events and the hormones controlling the arrested state. Here, we show that diapause is regulated by an interplay between blood-borne metabolites and regulatory centers within the brain. Gene expression in the fat body, the insect equivalent of the liver, is strongly suppressed during diapause, resulting in low levels of tricarboxylic acid (TCA) intermediates circulating within the blood, and at diapause termination, the fat body becomes activated, releasing an abundance of TCA intermediates that act on the brain to stimulate synthesis of regulatory peptides that prompt production of the insect growth hormone ecdysone. This model is supported by our success in breaking diapause by injecting a mixture of TCA intermediates and upstream metabolites. The results underscore the importance of cross-talk between the brain and fat body as a regulator of diapause and suggest that the TCA cycle may be a checkpoint for regulating different forms of animal dormancy.

Abstract: Mechanisms controlling development, growth, and metabolism are coordinated in response to changes in environmental conditions, enhancing the likelihood of survival to reproductive maturity. Much remains to be learned about the molecular basis underlying environmental influences on these processes. C. elegans larvae enter a developmentally dormant state called L1 diapause when hatched into nutrient-poor conditions. The nematode pten homologue daf-18 is essential for maintenance of survival and germline stem cell quiescence during this period (Fukuyama et al., 2006; Sigmond et al., 2008), but the details of the signaling network(s) in which it functions remain to be elucidated. Here, we report that animals lacking both aak-1 and aak-2, which encode the two catalytic α subunits of AMP-activated protein kinase (AMPK), show reduced viability and failure to maintain mitotic quiescence in germline stem cells during L1 diapause. Furthermore, failure to arrest germline proliferation has a long term consequence; aak double mutants that have experienced L1 diapause develop into sterile adults when returned to food, whereas their continuously fed siblings are fertile. Both aak and daf-18 appear to maintain germline quiescence by inhibiting activity of the common downstream target, TORC1 (TOR Complex 1). In contrast, rescue of the lethality phenotype indicates that aak-2 acts not only in the intestine, as does daf-18, but also in neurons, likely promoting survival by preventing energy deprivation during L1 diapause. These results not only provide evidence that AMPK contributes to survival during L1 diapause in a manner distinct from that by which it controls dauer diapause, but they also suggest that AMPK suppresses TORC1 activity to maintain stem cell quiescence.

Abstract: Background: Diapause, a condition of developmental arrest and metabolic depression exhibited by a wide range of animals is accompanied by complex physiological and biochemical changes that generally enhance environmental stress tolerance and synchronize reproduction. Even though some aspects of diapause have been well characterized, very little is known about the full range of molecular and biochemical modifications underlying diapause in non-model organisms. Methodology/Principal Findings: In this study we focused on the parasitic wasp, Praon volucre that exhibits a pupal diapause in response to environmental signals. System-wide metabolic changes occurring during diapause were investigated using GC-MS metabolic fingerprinting. Moreover, proteomic changes were studied in diapausing versus nondiapausing phenotypes using a combination of two-dimensional differential gel electrophoresis (2D-DIGE) and mass spectrometry. We found a reduction of Krebs cycle intermediates which most likely resulted from the metabolic depression. Glycolysis was galvanized, probably to favor polyols biosynthesis. Diapausing parasitoids accumulated high levels of cryoprotective polyols, especially sorbitol. A large set of proteins were modulated during diapause and these were involved in various functions such as remodeling of cytoskeleton and cuticle, stress tolerance, protein turnover, lipid metabolism and various metabolic enzymes. Conclusions/Significance: The results presented here provide some first clues about the molecular and biochemical events that characterize the diapause syndrome in aphid parasitoids. These data are useful for probing potential commonality of parasitoids diapause with other taxa and they will help creating a general understanding of diapause underpinnings and a background for future interpretations.

Abstract: Recent studies dealing with adult (reproductive) diapause in the Coleoptera are reviewed, as a kind of supplement to the classic compendia. In the first two sections, the general characteristics of adult diapause are described and principal terms explained. Original articles dealing with 19 species from nine coleopteran families (Coccinellidae, Chrysomelidae, Bruchidae, Curculionidae, Carabidae, Silphidae, Scolytidae, Scarabaeidae, and Endomychidae) are reviewed. Finally attempts are made at generalisations from the papers reviewed, and hypotheses on diapause evolution are inferred. A polyphenic character of diapause is a prominent feature in C. septempunctata and L. decemlineata, but has been found also in other Coleoptera and in insects generally and often generates voltinism heterogeneity within populations.

Abstract: 1 The pine weevil Hylobius abietis is widely distributed in the Palaearctic region where it is a major pest. Although predominantly semi-voltine, with a 2-year life cycle, the generation time across its range can vary from 1 to 4 years. The duration of the life cycle and the seasonal timing of weevil activity affect the economic impact and management of this pest, all of which are likely to change in a warming climate. 2 To determine the effect of temperature and tree species on weevil growth and development, laboratory experiments were performed with eggs, larvae, prepupae, pupae and adults, using, as appropriate, the host species Scots pine Pinus sylvestris L. and Sitka spruce Picea sitchensis (Bong.) Carr. under constant or alternating temperatures. 3 The development rate was linearly related to temperature, with developmental thresholds for eggs, larvae and pupae of 8, 4.5 and 7.3 °C, respectively. Day-degrees were estimated for each life stage. Larval development was affected by tree species, being slower on Sitka spruce than on Scots pine, and was faster under alternating than constant temperatures. 4 The development time for prepupae was highly variable, with an apparent facultative prepupal diapause initiated by temperature. The temperature range 20–17.5 °C marked the transition between median prepupal development times of approximately 25 and 90 days. The prepupal stage may serve to minimize the risk of overwintering mortality in the pupal stage and help to synchronize the life cycle. 5 Larval and adult mass was positively related to developmental temperature, demonstrating an inverse temperature size rule, and weevils were heavier when developing on Scots pine than Sitka spruce. Development in alternating temperatures reduced weevil mass on Scots pine. The influence of temperature on weevil mass is likely to have a positive effect on fecundity and overwintering survival. The effects of climate change on development, voltinism and weevil mass are discussed.

Abstract: An insect's cold hardiness affects its potential to overwinter and outbreak in different geographic regions. In this study, we characterized the response of Helicoverpa zea (Boddie) pupae to low temperatures by using controlled laboratory measurements of supercooling point (SCP), lower lethal temperature (LT50), and lower lethal time (LLTime). The impact of diapause, acclimation, and sex on the cold hardiness of the pupae also were evaluated. Sex did not significantly affect the SCP, LT50, or LLTime. However, the mean SCP of diapausing pupae (-19.3°C) was significantly lower than nondiapausing pupae (-16.4°C). Acclimation of nondiapausing pupae to constant temperatures from 10 to 20°C before supercooling also produced a significantly lower SCP than nondiapausing pupae held at 25°C. The LT50s of nondiapausing and diapausing were not significantly different, but confirmed that H. zea pupae are chill-intolerant because these lethal temperatures are warmer than the corresponding mean SCPs. Diapausing pupae survived longer than nondiapausing pupae at the same, constant, cold temperatures, a finding consistent with the SCP results. Both of these results suggest enhanced cold hardiness in diapausing pupae. When laboratory results were compared with field temperatures and observed distributions of H. zea in the contiguous United States, the laboratory results corroborated what is currently perceived to be the northern overwintering limit of H. zea; approximately the 40th parallel. Moreover, our research showed that areas north of this limit are lethal to overwintering pupae not because of low temperature extremes, but rather the length of time spent at near-zero temperatures.

Abstract: Theoretically, asymmetric gene flow along an environmental gradient can limit species range expansion by keeping peripheral populations from locally adapting. However, few empirical studies have examined this potentially fundamental evolutionary mechanism. We address this possibility in the cricket Allonemobius socius, which exist along a season-length gradient where the probability of producing a single generation per year (univoltinism) increases with latitude. As the probability of univoltinism increases northwards, populations are expected to hedge their bets by producing a greater proportion of diapause eggs when exposed to a mild diapause cue. However, gene flow from southern populations may disrupt local adaptation in the north by reducing the proportion of diapause eggs (expected to be 100% in pure univoltine environments). This may limit range expansion along the northern periphery where A. socius compete with A. fasciatus, a sister species that exhibits an invariant diapause-only egg-laying strategy. To assess the potential for range limitation, we examined diapause incidence (the proportion of diapause eggs produced under diapause conditions), gene flow symmetry and population structure across nine A. socius populations. We found that gene flow was asymmetric and biased northwards towards the periphery. Furthermore, peripheral populations that inhabited pure univoltine environments produced numerous nondiapause eggs (a southern, bivoltine diapause phenotype), which we assume to be a suboptimal phenotype. These patterns suggest that asymmetric gene flow along the gradient constrains adaptation in peripheral populations, potentially constraining species range expansion.

Abstract: Dormancy can serve as an adaptation to persist in variable habitats and often is coupled with sex. In cyclically parthenogenetic rotifers, an asexual phase enables rapid population growth, whereas sex results in diapausing embryos capable of tolerating desiccation. Few studies have experimentally tested whether sex–dormancy associations in temporary waters reflect evolution in response to the short hydroperiod selecting for diapause ability. Here, we demonstrate evolution of higher propensity for sex and dormancy in ephemeral rotifer cultures mimicking temporary ponds, and lower propensity in permanent cultures. Results are consistent with rapid evolution, with evolutionary changes occurring in a short timeframe (385 days, ≤ 84 generations). We also provide insight into mechanisms for rapid evolution in basal metazoans, discussing potential roles of new mutations, recombination and clonal selection.

Abstract: Embryonic diapause is an evolutionary strategy by which a reversible arrest in embryo development occurs. In its two forms, facultative and obligate, it assures that offspring are born when optimal maternal and environmental conditions are present to ensure maximal survival. We have explored obligate delayed implantation in the mink (Neovison vison) over four decades: first by evaluation of the environmental regulation, then by determination of the pituitary factors that maintain diapause and provoke implantation followed by exploration of the ovarian contribution to the process. As the uterine environment is the proximal regulator of diapause, we employed a strategy of global gene analysis to discover differentially expressed pathways during embryo arrest and reactivation. These trials revealed that the synthesis of polyamines was increased in the uterus with reactivation of the embryo in vivo. Subsequent experiments demonstrated that the polyamine, putrescine, was capable of inducing escape of the embryo from obligate diapause, providing strong evidence that the paucity of polyamines induces developmental arrest, and reactivation is coupled to renewed uterine and/or embryonic synthesis of these polycations.

Abstract: The Indianmeal moth, Plodia interpunctella (Hubner) (Lepidoptera: Pyralidae), is a serious insect pest of stored products, and its late-instar larvae diapause as pre-pupae. Diapause induction in P. interpunctella was investigated for four populations obtained from Modesto, California, U.S.A.; Vancouver, British Columbia, Canada; and two locations from Winnipeg, Manitoba, Canada. Insects were reared at 25° C and 16:8 L:D for 9 days. The larvae were then either continuously maintained under those conditions or transferred to 25° C 8:16 L:D, 20° C 16:8 L:D, or 20° C 8:16 L:D, and the percent diapause was recorded. In the experiment with four populations, the highest diapause frequency was observed at 20° C 8:16 L:D. The two Winnipeg populations had significantly higher frequency of diapause than the California populations, indicating the increased frequency of diapause in populations from higher latitudes. In a second experiment, the Vancouver population was selected for diapause. Larvae were reared at 25° C 16:8 L:D for 9 days, then placed at 20° C 8:16 L:D for the rest of their development, and percent diapause was determined. Eggs laid by moths that completed diapause in this first (parental) generation were used to obtain a second generation (F1), and the experiment was repeated as in the first generation. Selection increased the frequency of diapause to 91%, compared to 26% in the unselected population, after selecting over two generations. The narrow sense heritability of selection in P. interpunctella was 0.39 in the first selection, and 0.82 in the second. This study has shown that both low temperature and short photoperiod are required to induce diapause in North American populations of P. interpunctella, and that selection can increase diapause in a few generations.

Abstract: Embryos of the annual killifish Austrofundulus limnaeus can enter into dormancy associated with diapause and anoxia-induced quiescence. Dormant embryos are composed primarily of cells arrested in the G1/G0 phase of the cell cycle based on flow cytometry analysis of DNA content. In fact, most cells in developing embryos contain only a diploid complement of DNA, with very few cells found in the S, G2, or M phases of the cell cycle. Diapause II embryos appear to be in a G0-like state with low levels of cyclin D1 and p53. However, the active form of pAKT is high during diapause II. Exposure to anoxia causes an increase in cyclin D1 and p53 expression in diapause II embryos, suggesting a possible re-entry into the cell cycle. Post-diapause II embryos exposed to anoxia or anoxic preconditioning have stable levels of cyclin D1 and stable or reduced levels of p53. The amount of pAKT is severely reduced in 12 dpd embryos exposed to anoxia or anoxic preconditioning. This study is the first to evaluate cell cycle control in embryos of A. limnaeus during embryonic diapause and in response to anoxia and builds a foundation for future research on the role of cell cycle arrest in supporting vertebrate dormancy.

Abstract: We studied the seasonal lipid dynamics of Calanus finmarchicus from Loch Etive, a semi-enclosed fjordic environment on the west coast of Scotland, in relation to the diapause behavior of this species. Levels of total lipid and triacylglycerol in individual copepodid stage V (CVs) exhibited clear seasonal trends, with highest levels in June and progressively decreasing through late summer to winter. Wax esters in CVs were more variable, but followed a similar pattern. An index of the level of unsaturation of wax esters, effectively an indicator of the levels of polyunsaturated fatty acids in the wax ester reserves, were highest in midsummer and declined progressively through autumn and winter. Fatty acid analysis of total lipid in the CVs confirmed that the amounts of polyunsaturated fatty acids in the wax esters decreased, while amounts of saturated and monounsaturated fatty acids remained comparatively stable. Polyunsaturated wax esters are selectively catabolized by C. finmarchicus during diapause. Previous studies have linked unsaturation of wax esters in calanoid copepods to the initiation of diapause and buoyancy control, and we hypothesize that selective catabolism of polyunsaturated wax esters is linked to the processes of diapause termination and ascent to surface waters. The copepod Calanus finmarchicus is an important trophic link between primary producers and a number of commercially important fish species in the North Atlantic and peripheral ecosystems (Conover et al. 1995). A key, yet little understood aspect of the life cycle of C. finmarchicus is its overwintering behavior when it enters into diapause, effectively a state of dormancy when metabolic processes are greatly reduced (Hirche 1996). Mechanisms controlling diapause have remained elusive because the initiation and termination of diapause is highly variable between regions and not linked to the physical environment (Johnson et al. 2008). Threshold levels of total lipid are thought to be involved in controlling diapause, the hypothesis being that copepods must accumulate a minimum level of lipid before diapause is initiated (Rey-Rasset et al. 2002; Irigoien 2004). These large lipid stores are accumulated during copepodid stages IV and V (hereafter referred to as CIV and CV), and are essential for processes such as metabolic energy generation, diapause, gonad maturation, and egg production (Lee et al.

Abstract: Voltinism of herbivorous insects can vary depending on environmental conditions. The leaf beetle Phratora vulgatissima L. is univoltine in Sweden but will sometimes initiate a second generation in short-rotation coppice (SRC) willow plantations. 2. The study investigated whether increased voltinism by P. vulgatissima in plantations can be explained by (i) rapid life-cycle development allowing two generations, or (ii) postponed diapause induction on coppiced willows. 3. In the field, no difference was found in the phenology or development of first-generation broods between plantations (S. viminalis) and natural willow habitats (S. cinerea). However, the induction of diapause occurred 1-2 weeks later in SRC willow plantations. 4. Laboratory experiments indicated no genetic difference in the critical day- length for diapause induction between beetles originating from plantations and natural habitats. Development time was unaffected by host-plant quality but critical day-length was prolonged by almost an hour when the beetles were reared on a non-preferred willow species (S. phylicifolia). When reared on new leaves from re-sprouting shoots of recently coppiced willow plants, diapause incidence was significantly less than when the beetles were reared on mature leaves from uncoppiced plants. 5. The study suggests that P. vulgatissima has a plastic diapause threshold influenced by host-plant quality. The use of host-plant quality as a diapause-inducing stimulus is likely to be adaptive in cases where food resources are unpredictable, such as when new host-plant tissue is produced after a disturbance. SRC willows may allow two beetle generations due to longer growing seasons of coppiced plants that grow vigorously.

Abstract: Due to the risk of extinction and ornamental value of the swallowtail butterfly, Sericinus montelus Gray (Lepidoptera: Papilionidae) in China, knowledge about local adaptations is important for the conservation and economical utilization of the species. In the present study, photoperiodic diapause induction and diapause intensity of S. montelus populations from Jiamusi (46°37′N), Beijing (40°15′N), Zibo (36°48′N), Fangxian (32°36′N), Wuhan (30°33′N) and Huaihua (27°33′N) were characterized at 25°C. Logistic regression analysis revealed a significant population × hours of light interaction, confirming that photoperiodic responses varied among populations. The critical photoperiod was positively correlated with latitude and increased toward the north at a rate of about 1 h for each 6.67 degrees of latitude. Survival analyses indicated that survival time of diapausing pupae before adult eclosion differed significantly among populations at 25°C and 16 : 8 L : D h. The mean duration of pupal diapause was also positively correlated with latitude. Our study reveals geographic variation in the critical photoperiod for diapause induction and in diapause intensity of S. montelus. These results provide useful information for our general understanding about seasonal adaptation in insects and may also be used to predict how geographic populations respond to climate warming.

Abstract: Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), overwinter as diapausing adults in North America. Overwintering adults were collected near Stoneville, MS from blooming henbit, Lamium amplexicaule L., and from plant debris during December and January and dissected to determine their reproductive status. Averaged over four winters, male and female tarnished plant bugs collected from henbit terminated diapause at a significantly higher rate than males and females from plant debris during each week of December and the first week of January. Both sexes in each habitat were nearly all reproductive by the end of January. Adults overwintering in plant debris terminated diapause during January in the absence of a food stimulus in all 5 yr studied. This emergence was thought to be controlled by an internal clock. Laboratory and field studies showed that emergence from diapause could be influenced by food, sex, and temperature. Adults overwintering on a suitable food source, blooming henbit, terminated diapause during December in the 4 yr studied, and males terminated diapause more rapidly than females. Food quality was important in emergence from diapause, and females on blooming henbit terminated diapause at a significantly higher rate than females on nonblooming mustard, Brassica juncea (L.) Cosson. Laboratory tests showed that diapausing adults reared in the laboratory and held at a diapause-maintaining photoperiod of 10:14 (L:D) h could be terminated from diapause by using food and temperature stimuli. The lower thermal threshold for development to reproductive adults was found to be near 10°C. The ability of diapausing adults to respond to food and temperature stimuli in December can enable tarnished plant bugs to take advantage of warm winters and winter hosts to produce a new generation earlier.

Abstract: The Asian corn borer Ostrinia furnacalis (Guenee) enters facultative diapause as fully-developed larvae in response to short-day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28°46′N, 115°50′E) enter diapause in response to short day-lengths (D strain), even at the high temperatures whereas moths from Ledong (18°47′N, 108°89′E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 °C. The moths, both reciprocal crosses and backcrosses, show a clear long-day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day-length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short-day photoperiodic response at the lower temperature of 22 °C, indicating that the N strain still has the capacity to enter a photoperiodically-induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 °C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.

Abstract: The maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), is of economic importance throughout sub-Saharan Africa. The seasonal activity pattern of this pest is characterized by two to three distinct generations during spring and summer followed by a diapause period of approximately six months during autumn and winter. Genetically modified Bt maize (MON810) that expresses an insecticidal Cry1Ab protein has been deployed in South Africa since 1998 to manage stem borers. The first report of field resistance of B. fusca to Bt maize was made during the 2006 cropping season. Resistant strains of this pest are expected have reduced fitness compared to susceptible individuals. Information regarding fitness of resistant individuals that survive on Bt maize could contribute to the understanding of resistance evolution as well as to development of improved resistance management strategies. Life history parameters of different B. fusca populations were compared in a laboratory study using diapause (spring) as well as second-generation (summer) populations. Sex ratio, pupal mass, fecundity and longevity of moths of field-collected Bt-resistant and susceptible B. fusca populations were compared. Slight adverse effects of Bt maize on fitness of the resistant summer-population were observed. The sex ratio was biased towards males in some resistant populations and towards females in susceptible populations. The resistant population had a lower mean pupal mass, shorter longevity of moths and reduced fecundity.

Abstract: Embryos of the annual killifish Austrofundulus limnaeus can enter into a state of metabolic dormancy, termed diapause, as a normal part of their development. In addition, these embryos can also survive for prolonged sojourns in the complete absence of oxygen. Dormant embryos support their metabolism using anaerobic metabolic pathways, regardless of oxygen availability. Dormancy in diapause is associated with high ATP and a positive cellular energy status, while anoxia causes a severe reduction in ATP content and large reductions in adenylate energy charge and ATP/ADP ratios. Most cells are arrested in the G1/G0 phase of the cell cycle during diapause and in response to oxygen deprivation. In this paper, we review what is known about the physiological and biochemical mechanisms that support metabolic dormancy in this species. We also highlight the great potential that this model holds for identifying novel therapies for human diseases such as heart attack, stroke and cancer.