Adult Dormancy Research Articles

Morphology, Diet, and Temperature-Dependent Host-Free Survival of the Boll Weevil, Anthonomus grandis (Coleoptera: Curculionidae).

The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is an important pest of cotton (Gossypium spp. (Malvales: Malvaceae)) in South America, Mexico, and southernmost Texas in the United States. A key factor in the persistence of the boll weevil is its ability to survive the noncotton season. Mechanisms facilitating this survival in subtropical and tropical areas are incompletely known, and our understanding has been further complicated by recent reports of overwintering on noncotton hosts. In addition, the nature and even existence of the adult dormancy, and validity of the criteria used to distinguish it, have been questioned. We manipulated the boll weevil diet to produce a range of diapause responses and observed the corresponding host-free survival patterns. The estimated proportion of diapause was associated with subsequent survival. In addition, different diets producing similar incidences of diapause resulted in substantially different host-free longevity, and the longest survival was observed for weevils fed bolls as adults. Survival patterns exhibited a negative temperature dependence except for the lowest observed temperature (12.8°C), where survival was reduced compared with that at 18.3°C. This suggests chronic chilling injury in response to extended exposure to low, above freezing temperatures. All but the highest temperature (29.4°C) facilitated survival >6 mo, and survival of >1 yr was observed at 18.3°C. The temperatures permitting the greatest survival are typical for many subtropical and tropical regions during the noncotton season, indicating that diapausing boll weevils are capable of surviving the noncotton season in these regions without the benefit of presumptive noncotton hosts.

Behavioral Senescence and Aging-Related Changes in Motor Neurons and Brain Neuromodulator Levels Are Ameliorated by Lifespan-Extending Reproductive Dormancy in Drosophila.

The lifespan of Drosophila melanogaster can be extended substantially by inducing reproductive dormancy (also known as diapause) by lowered temperature and short days. This increase of longevity is accompanied by lowered metabolism and increased stress tolerance. We ask here whether behavioral senescence is ameliorated during adult dormancy. To study this we kept flies for seven or more weeks in normal rearing conditions or in diapause conditions and compared to 1-week-old flies in different behavioral assays of sleep, negative geotaxis and exploratory walking. We found that the senescence of geotaxis and locomotor behavior seen under normal rearing conditions was negligible in flies kept in dormancy. The normal senescence of rhythmic activity and sleep patterns during the daytime was also reduced by adult dormancy. Investigating the morphology of specific neuromuscular junctions (NMJs), we found that changes normally seen with aging do not take place in dormant flies. To monitor age-associated changes in neuronal circuits regulating activity rhythms, sleep and walking behavior we applied antisera to tyrosine hydroxylase (TH), serotonin and several neuropeptides to examine changes in expression levels and neuron morphology. In most neuron types the levels of stored neuromodulators decreased during normal aging, but not in diapause treated flies. No signs of neurodegeneration were seen in either condition. Our data suggest that age-related changes in motor neurons could be the cause of part of the behavioral senescence and that this is ameliorated by reproductive diapause. Earlier studies established a link between age-associated decreases in neuromodulator levels and behavioral decline that could be rescued by overexpression of neuromodulator. Thus, it is likely that the retained levels of neuromodulators in dormant flies alleviate behavioral senescence.

Characterization of Reproductive Dormancy in Male Drosophila melanogaster.

Insects are known to respond to seasonal and adverse environmental changes by entering dormancy, also known as diapause. In some insect species, including Drosophila melanogaster, dormancy occurs in the adult organism and postpones reproduction. This adult dormancy has been studied in female flies where it is characterized by arrested development of ovaries, altered nutrient stores, lowered metabolism, increased stress and immune resistance and drastically extended lifespan. Male dormancy, however, has not been investigated in D. melanogaster, and its physiology is poorly known in most insects. Here we show that unmated 3–6 h old male flies placed at low temperature (11°C) and short photoperiod (10 Light:14 Dark) enter a state of dormancy with arrested spermatogenesis and development of testes and male accessory glands. Over 3 weeks of diapause we see a dynamic increase in stored carbohydrates and an initial increase and then a decrease in lipids. We also note an up-regulated expression of genes involved in metabolism, stress responses and innate immunity. Interestingly, we found that male flies that entered reproductive dormancy do not attempt to mate females kept under non-diapause conditions (25°C, 12L:12D), and conversely non-diapausing males do not mate females in dormancy. In summary, our study shows that male D. melanogaster can enter reproductive dormancy. However, our data suggest that dormant male flies deplete stored nutrients faster than females, studied earlier, and that males take longer to recover reproductive capacity after reintroduction to non-diapause conditions.

Persistence of a Wolbachia infection frequency cline in Drosophila melanogaster and the possible role of reproductive dormancy.

Field populations of arthropods are often polymorphic for Wolbachia but the factors maintaining intermediate Wolbachia frequencies are generally not understood. In Drosophila melanogaster, Wolbachia frequencies are highly variable across the globe. We document the persistence of a Wolbachia infection frequency cline in D. melanogaster populations from eastern Australia across at least 20 years, with frequencies generally high in the tropics but lower in cool temperate regions. The results are interpreted using a model of frequency dynamics incorporating cytoplasmic incompatibility (CI), imperfect maternal transmission and Wolbachia effects on fitness. Clinal variation is less pronounced in eastern North America which may reflect annual recolonization at higher latitudes. Limited samples from Africa from latitudes matching our tropical and subtropical samples from Australia and North America show comparably high infection frequencies, but some equatorial samples show lower frequencies. Adult dormancy across cold periods may contribute to the Australian Wolbachia cline. Infected flies exposed to cold conditions for an extended period had reduced fecundity and viability, an effect not evident in unexposed controls. These fitness costs may contribute to the relatively low Wolbachia frequencies in Australian temperate areas; whereas different processes, including CI induced by young males, may contribute to higher frequencies in tropical locations.

Malaria: How vector mosquitoes beat the heat.

Intensive longitudinal sampling of malaria mosquitoes in the African semi-desert reveals that three morphologically indistinguishable species have distinctive strategies for surviving the dry season. See Letter p.387 Malaria-carrying mosquitoes disappear in the dry season but appear suddenly when the rains come to sub-Saharan Africa. Their behaviour during the dry half of the year has long been something of a mystery. Here, Tovi Lehmann and colleagues report five-year surveys of mosquito densities throughout that reveal seasonal patterns in the population dynamics of three main vector species, and use these to infer dry-season behaviour. In two species (Anopheles arabiensis and A. gambiae s.s.) the dynamics are consistent with long-distance migration, and in the third (Anopheles coluzzii) with dry-season adult dormancy or aestivation. These natural history discoveries offer fundamental opportunities to improve malaria control, which remains a major public health challenge.

Storage of Pentatomid Eggs in Liquid Nitrogen and Dormancy of Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead (Hymenoptera: Platygastridae) Adults as a Method of Mass Production.

The eggs of pentatomid species were evaluated to parasitism by Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead after storage in liquid nitrogen. Adults which emerged from stored eggs were kept at 18°C for 120 and 180days to investigate whether adult dormancy could be associated with host egg storage in liquid nitrogen as a method of mass production of these egg parasitoids. Eggs of Nezara viridula (L.) and Acrosternum pengue (Rolston) were successfully parasitized by T. basalis, as well as Piezodorus guildinii (Westwood) and Dichelops furcatus (F.) by T. podisi. The eggs of Edessa meditabunda (F.) were not parasitized by T. basalis. The emergence of T. podisi from eggs of Euschistus heros (F.) and Podisus nigrispinus (Dallas) stored for 6months was lower than the control. Females of T. basalis and T. podisi that emerged from stored eggs were kept in dormancy at 18°C. Longevity of T. basalis was influenced by the storage time and sex, but not by the interaction of sex and storage time. For T. podisi, longevity was influenced by the storage time, sex, and by the interaction of sex and storage time. For T. basalis, storage in liquid nitrogen did not affect the fecundity of quiescent females, while the number of parasitized eggs by T. podisi decreased after storage. By the joint use of these techniques, it is possible to optimize mass production of T. basalis so that its life cycle can be monitored and synchronized with the life cycle and availability of hosts.

Biological Flora of the British Isles:Gymnadenia conopsea s.l.

SummaryThis account presents information on all aspects of the biology ofGymnadenia conopsea(L.)R.Browns.l. (FragrantOrchid) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of theBiologicalFlora of theBritishIsles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation.Most available information was published before recent revisions in taxonomy split what had been known asGymnadenia conopseainto three separate species, now designatedG. borealis(Druce)R.M.Bateman,Pridgeon &M.W.Chase,G. conopsea(L.)R.Brown andG. densiflora(Wahlenb.)Dietrich. Although the three newly accepted species have at least partial reproductive isolation, they have numerous morphological and ecological similarities. Some recent work still refers toG. conopsea s.l. because of difficulties in distinguishing between the species, and inertia in adoption of the new taxonomy. Wherever possible, differences betweenG. borealis,G. conopsea s.s. andG. densifloraare highlighted.Gymnadenia conopsea s.l. is a perennial, terrestrial orchid that is widely distributed acrossEurasia. The three segregate species are all considered native.G. conopsea s.s. (ChalkFragrantOrchid) occurs mainly in the southern half ofBritain, where it is most commonly observed in dry calcareous grasslands and pastures.G. densiflora(MarshFragrantOrchid) occurs in damp calcareous marshes, fens and dune slacks in England and Wales; it is rare in Scotland but frequent in Ireland.G. borealis(HeathFragrantOrchid) is mainly found on hill pastures inWales, northernEngland andScotland. The three species all avoid shade, being most abundant in open habitats.Although the three segregate species cannot always be reliably distinguished on the basis of morphological characteristics, diagnostic features include plant height, leaf width and disposition, density of flowers in the inflorescence, shape of the labellum, spur width, and odour and colour of the flowers. Additionally, several cytotypes withinG. conopsea s.s. have been observed inCentralEurope. These often grow in mixed‐ploidy populations; in contrast, the species appears to be predominantly diploid inBritain.Gymnadenia conopsea s.l. is a non‐bulbous geophyte. Leaves emerge in spring, and flowering takes place between the end of June and the beginning ofAugust. Vegetative adult dormancy – the failure of above‐ground parts to appear in a growing season, followed by reappearance of full‐sized photosynthetic plants in subsequent years – has been observed. Such dormancy rarely lasts longer than 1 year.The flowers ofG. conopsea s.l. are arranged in a spike. The species is self‐compatible but dependent on pollinators for successful pollination and fruit set. The most frequent pollinators are diurnal and nocturnal Lepidoptera. Pollinators are rewarded with abundant nectar produced within the long floral spur. In many populations, fruit set is > 90%.AlthoughG. conopsea s.l. is widely distributed and can be locally abundant, the number of populations and size of populations in Britain have declined markedly during recent decades, mostly due to habitat destruction, ploughing of old fields and drainage. Because the distribution of the segregate species has been poorly documented, their conservation status is not well known. Conservation of remaining populations and restoration of degraded populations require reinstatement of appropriate management regimes (late summer/autumn mowing or grazing), combined with more detailed inventories of the three species.

Biological flora of the British Isles: Orchis anthropophora (L.) All. (Aceras anthropophorum (L.) W.T. Aiton)

Summary1. This account presents information on all aspects of the biology of Orchis anthropophora (L.) All. (Man Orchid) that are relevant to understanding its ecological characteristics and behaviour. The following topics are presented within the framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history, and conservation.2. Orchis anthropophora is a native species in Britain, where it occurs predominantly in chalk and limestone grassland and dune grassland. It can also be found along field margins and in old abandoned chalk pits and limestone quarries, where it is usually found at the foot of slopes. It also grows on road verges and sometimes in quite dense scrub. Orchis anthropophora tolerates some shade, but it flowers most profusely in open conditions. It is a common species in the Mediterranean region.3. Orchis anthropophora is wintergreen and has leaves throughout the winter. Flowering takes place between mid‐May and mid‐June. Vegetative adult dormancy – the failure of above‐ground parts to appear in a growing season, followed by the reappearance of full‐sized photosynthetic plants in subsequent seasons – has been observed. In most cases, dormancy does not last longer than 1 year. Orchis anthropophora is long‐lived (half‐life of cohorts ranges from 4.0 to 7.8 years).4. Orchis anthropophora is not autogamous, and pollinators are required for successful pollination and fruit‐set. Flowers are predominantly pollinated by beetles and sawflies. Terpenes are the major compounds of the floral scent profile of O. anthropophora. Natural levels of fruit‐set are generally low. Recorded values are mostly <20% but reached >80% in a population in southern France.5. Orchis anthropophora hybridizes with several other species in the genus Orchis, including O. italica, O. simia, O. purpurea and O. militaris. Intergeneric hybrids have been reported with Barlia, Dactylorhiza and Neotinea. In Britain, hybrids with O. simia and O. purpurea have been reported.6. Orchis anthropophora has declined markedly in Britain during the last century, and at present, it is rare and classified as endangered. Very few new populations are becoming established, and many populations have become extinct, mainly because of agricultural intensification (ploughing and fertilization of old fields). Conservation of the remaining populations requires moderate grazing by sheep to maintain a short turf and to promote seedling recruitment.

Biological Flora of the British Isles:Spiranthes spiralis(L.) Chevall.

Summary1. This account presents information on all aspects of the biology ofSpiranthes spiralis(L.) Chevall. that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of theBiological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation.2. Spiranthes spiralisis a long‐lived orchid species that is widely distributed in the southern part of the British Isles, southern Europe and the Mediterranean. It is native to Britain. Its most characteristic habitats are unimproved, well‐grazed grasslands on dry calcareous soils, particularly chalk and limestone, cliff‐tops and grassy coastal dunes. It can also be found in garden lawns and, less frequently, in slightly acidic heathland habitat. It occurs on both dry and wet soils, but it does not tolerate heavy shading.3. Spiranthes spiralisis a non‐bulbous geophyte regenerating by sexual reproduction and by vegetative spread, although the latter is limited. Vegetative reproduction involves the growth of a lateral bud on the underground stem. The new plant forms its own tubers, and eventually the connection between the mother plant and the vegetatively produced daughter plant withers away.4. The main perennating organ is a tuberous root. In most years, the tuber generates a rosette of expanded leaves, and at the end of every year of the plant’s life, the tuber is completely replaced. In some cases, however, only part of the reserves is exhausted in flowering and, when this happens, a tuber may survive for several years. Vegetative adult dormancy – the failure of above‐ground parts to appear in a growing season, followed by reappearance of full‐sized photosynthetic plants in subsequent seasons – has been observed. It most commonly lasts for only 1 year, but sometimes plants can remain dormant for several years.5. The species is not autogamous and pollinators – mainly bumblebees and bees – are necessary for successful pollination and fruit set. Natural levels of fruit set are usually <50%. Hand‐pollination increases fruit set toc. 75%, indicating that reproduction is to some extent pollen‐limited. Sexual reproduction comes at a cost, and few individuals flower for two or more consecutive years. Within fruits many very small seeds are produced, but most are dispersed to a distance of less than a few dm from maternal plants, leading to strongly aggregated distribution patterns and significant spatial genetic structuring within natural populations.6. Spiranthes spiralishas suffered significant declines in distribution in Britain and other European countries. In Britain, populations were lost from many sites before 1930, when many pastures were re‐sown or converted to arable land. Losses of populations due to agricultural intensification (ploughing of old fields and fertilization) still occur and are the major causes of the decline of the species. Conservation of remnant populations primarily requires the maintenance of a short turf by grazing, most often by sheep. Ideally, grazing should be suspended during flowering and seed set, allowing new recruits to become established and adult plants to flower profusely and to produce seeds.

Costs and benefits of fruiting to future reproduction in two dormancy‐prone orchids

Summary Reproduction is expected to occur at a cost to survival, growth or future reproduction. However, trade‐offs in long‐lived, clonal herbs have proven difficult to assess, particularly when they are prone to adult dormancy. We assessed the costs of fruiting in a study of two species of lady's slipper orchid, Cypripedium candidum and C. parviflorum, growing sympatrically in a wet meadow in north‐eastern Illinois, USA, from 2000 to 2005. First, we characterized flowering and fruiting in both populations. We found some differences between species, with 68.6 ± 5.7% (mean ± SE) and 43.5 ± 1.4% of sprouting plants flowering, while 33.6 ± 10.0% and 33.5 ± 8.1% of flowering plants fruited in C. candidum and C. parviflorum, respectively. Next, we tested the survival, sprouting and flowering response to current fruiting using multistate mark–recapture statistics. The best‐fit model posited no cost of fruiting. However, according to a model parsimonious with the best‐fit model, fruiting may have resulted in a small cost to survival visible primarily in small‐sized individuals of C. parviflorum (decrease from 0.846 in non‐fruiting but flowering plants to 0.824 in fruiting plants). In all cases, fruiting resulted in an increased probability of future flowering, suggesting that reproduction may have a higher priority in resource allocation than survival. Finally, we tested the effects of fruiting on future fruiting using logistic regression for two years in which fruiting was particularly high, but detected no change in the probability of fruiting after fruiting. Fruiting may increase in response to internal cues, perhaps related to nutrient uptake or storage, in addition to the obvious effects of pollination. The result may be that plants with greater access to nutrients or with greater stored reserves are more likely to flower each season. We suggest a need for further research exploring the internal mechanisms governing fruiting response in long‐lived, clonal herbs.

Survival costs of adult dormancy and the confounding influence of size in lady's slipper orchids, genus Cypripedium

Adult whole‐plant dormancy is a phenomenon in which a perennial, herbaceous plant does not sprout for one or more years. Although previous studies have noted a cost of dormancy to survival, none have accounted for the potentially confounding influence of size variation on this relationship. I asked whether the probabilities of dormancy and survival in dormancy‐prone plants vary with size, possibly creating the appearance of a life‐history tradeoff between survival and dormancy. I censused sympatric populations of three lady's slipper orchid taxa, Cypripedium parviflorum, C. candidum, and C.×andrewsii, in an 11‐year study (1994 to 2004) at Gavin Prairie, Illinois, USA. Annual dormancy and survival trends were modeled using Cormack‐Jolly‐Seber mark‐recapture analysis, while stage‐specific survival and stratum‐transitions (i.e. probability of transitioning among stages conditional upon survival) were modeled with multi‐strata mark‐recapture analysis. Annual dormancy probabilities and transition probabilities to and from dormancy varied synchronously among taxa, while trends in survival did not. Both survival and dormancy varied with number of sprouts in the previous year, positively in the case of the former and negatively in the case of the latter. Accounting for plant size in this way eliminated any variation in survival by life‐history stage, with dormant plants surviving at the same rate as non‐dormant plants of the same size. Transitions among stages did not vary with plant size. My results suggest common climatic cues to dormancy, and suggest caution in inferring costs of dormancy from studies in which plant size is not controlled, as such costs may be artifacts of smaller plants being more dormant‐prone and less likely to survive.

Population viability analysis of Cypripedium calceolus in a protected area: longevity, stability and persistence

Summary 1 Cypripedium calceolus L. is an emblematic long-lived clonal orchid which has suffered an alarming decline throughout Eurasia. We performed a population viability analysis on three island populations in a protected area to estimate population viability and thus to gain a better understanding of the species and its needs. We developed a 10-stage matrix model, comprising the seed bank, the first 4 years underground, juveniles, young and adult clump stages and three dormant stages, from an 11-year census. 2 All analyses indicate that the three populations have remarkably slow and stable dynamics, with stochastic growth rates close to 1 after 100 years and very slow convergence to equilibrium. The system is probably stabilized by the long life span of clumps (mean longevity from 110 to 350 years). Retrospective and perturbation analyses showed that adult dormancy had an important role in the dynamics, and adult survival and seed persistence were key factors in maintaining population stability and persistence. 3 A young, uniformly distributed population had fewer, shorter lived adult clumps than two older, aggregated populations. Although no perceptible change was predicted for the next 100 years, the younger population was more sensitive to environmental variations and may go extinct in the next 250‐500 years, depending on longevity of the seed bank. 4 C. calceolus populations can persist in a protected area where there are only slow changes in habitat through secondary forest succession. The dramatic decrease in C. calceolus population size and area over 20 years in Eurasia suggests that many populations have experienced unforeseeable extrinsic disturbances or unfavourable habitat disturbances. 5 Our Population Viability Analysis indicated the importance of habitat vs. individual conservation for the protection of C. calceolus populations. As this species is usually found within rich orchid communities, it should be used as an umbrella species in management plans.

Effects of photoperiod and temperature on adult oligopause of Aphelinus asychis and larval diapause of A. albipodus (Hymenoptera: Aphelinidae)

The effects of photoperiod and temperature on the dormancy of two aphid parasitoids in Japan, Aphelinus asychis and A. albipodus, were studied in the laboratory. Adult (reproductive) dormancy was induced in A. asychis under 10L : 14D at moderate temperatures and under 15L : 9D at low temperatures. Dormant adults started oviposition 6–17 d after emergence under 10L : 14D at 15 and 18°C. Transferring newly emerged adults from 10L : 14D at 15 and 18°C to 15L : 9D at 20°C caused an apparent reversal of dormancy induction within 1–2 d. It was believed that adult dormancy in A. asychis conforms to “oligopause” rather than “diapause” sensu Mansingh (1971). Adults of A. asychis showed an apparent variation in abdominal coloration from yellowish brown to black. The proportion of females with dark abdominal coloration was higher under 10L : 14D than under 15L : 9D and high at lower temperatures. We regarded this polyphenism as a part of the “diapause syndrome” because oligopause and abdominal coloration were controlled by the same environmental factors. Aphelinus albipodus entered diapause as last instar larvae. The critical photoperiod for diapause induction was 11–12 h at 18°C, and diapause was terminated within six weeks by cold treatment (10L : 14D, 5°C).

Overwinter Survival of Boll Weevil (Coleoptera: Curculionidae) in Southern Texas: Evidence and Significance of Reproductive Diapause

Cohorts of adult boll weevils, Anthonomus grandis grandis Boheman, subjected to selected cotton diet regimens in two experiments, exhibited one or more of the classic symptoms of reproductive diapause. In both sexes, a limited diet of cotton squares or bolls conferred the ability to survive for considerable periods (up to 162 d) without subsequent feeding. An extended period of adult dormancy was evident among cohorts monitored during 1982-1983, although this was less evident among cohorts monitored in a second experiment (1983-1984). Despite such empirical evidence of dormancy, field surveys consistently indicated an extreme rarity or absence of dormant adult boll weevils in sites of deciduous leaf litter, bunchgrasses, and other types of conventional habitat that are generally considered preferred overwintering sites in temperate environments. Several explanations for these apparent anomalies are proposed, and the general significance of boll weevil diapause in subtropical environments is discussed.

Physical and Physiological Changes in the Adult Monterey-Pine Cone Beetle, Conophthorus radiatae (Coleoptera: Scolytidae)1

The adult respiration rate is significantly lower during the overwintering or “inactive” period than during the post-emergence or “active” period. It appears that respiration rate could be used as an index of the physiological state of adults. Flight muscles and ovaries are undeveloped in overwintering adults until just prior to emergence. Sperm in the spermathacae of some overwintering females demonstrates pre-emergence mating and indicates inbreeding. High humidity and warm temperature treatment of overwintering cones results in adult emergence. Emerged adults have fully developed flight muscles and elongating ovarioles. The adult dormancy period should be referred to as a quiescence.