Effects of changing photoperiods in the life cycle regulation of the comma butterfly, Polygonia c-album (Nymphalidae)

Abstract. 1. Regulation of adult reproductive diapause and seasonal polyphenism was studied in two populations of the comma butterfly, Polygonia c-album (L.) (Nymphalidae), from Stockholm, Sweden, and Oxford, England.
2. In the univoltine Stockholm population short and long constant day-lengths (in the range 12–22 h) at 20°C were ineffective in averting the production of the dark, generally diapausing, morph, but the non-diapausing light morph could be produced if daylengths were increased during larval development. The procedure was especially effective with increases from 12 to 22 h, but the tendency was the same with a more realistic increase, from 18 to 20 h.
3. In the partially bivoltine English population a critical constant day-length for morph and diapause induction was found between 12 and 18 h. Decreasing daylengths above the critical daylength early or late in larval development resulted in production of the diapausing morph.
4. These results suggest a system for environmental control where day-lengths which increase throughout the larval period indicate an early date before summer solstice, meaning that there is sufficient time for a second generation of offspring to reach the hibernating adult stage before winter. The ecological significance of the results is discussed.     

Phenotypic induction in Pieris napi L.: role of temperature and photoperiod in a coastal California population

Abstract. 1. Californian Pieris napi have previously been reported as producing dark-veined and light-veined adults from diapausing and. non-diapausing pupae respectively; the converse has not been reported.
2. A population of the coastal subspecies venosa from Monterey County was examined to determine whether pupal temperature exposure was involved in proximate control of seasonal phenotypes.
3. When reared under continuous light at 25°C this stock produced seventeen diapause pupae, thirteen of which have eclosed yielding typical dark-veined adults, and thirty-eight non-diapause pupae.
4. Of fifteen non-diapause pupae held in a dark box at 25°C, fourteen produced typical light-veined adults and one produced a dark-veined individual of intermediate phenotype.
5. Of twenty-three non-diapause pupae held in a dark box at 10°C for 24 days, twenty-two produced dark-veined butterflies of intermediate phenotype and one produced a light-veined adult.
6. When the experiment was repeated with an inland, population of subspecies microstriata , which is normally univoltine and monophenic, the temperature effect on phenotype was still present but less pronounced.
7. The nature of phenotypic determination is reviewed with particular regard for the developmental environment of butterflies from diapaused pupae. The thermal environment of reactivating diapausers, rather than the diapause state itself, may determine adult phenotype.     

Selection for discontinuous life-history traits along a continuous thermal gradient in the butterfly Aricia agestis

Abstract.  1. Voltinism may be conceptualised as the product of development rate and the timing of diapause – two components that together translate gradual environmental variation, through periods of growth and development, into 'generational units'. This may result in very different selection pressures on diapause induction and development time in populations with different numbers of generations per year.
2. Developmental data from univoltine and bivoltine populations of the butterfly Aricia agestis (Lepidoptera: Lycaenidae) in North Wales were used to examine larval development time and the timing of diapause, and their contribution towards voltinism in populations that occur at the same latitude and in geographic proximity to one another along a thermal gradient.
3. The critical photoperiod for diapause induction in univoltines and bivoltines from the same latitude differed by more than 1.5 h.
4. Development time also differed significantly between these populations, in line with predictions that bivoltines would need to exhibit shorter development times in order to achieve two complete generations per year. Shorter development times for bivoltines result in lower pupal weights, suggesting a trade-off exists between generation number and body size that may dictate the position of the transition zone between the two life-history strategies. Analysis of development times in a third population, from southern England, with greater thermal availability than those from North Wales, further supports this hypothesised trade-off.
5. To achieve the conversion of a continuous thermal gradient into the binary biological response from univoltism to bivoltism, bivoltines speed up development, reduce adult body size and shift their diapause induction response.     

Over-wintering stage polymorphism of a bruchine beetle: geographical variation in optimal diapause strategy

Abstract.  1. Most temperate insects undergo diapause at a specific developmental stage to overcome severe winters. The bruchine beetle Bruchidius dorsalis in a warmer region in Japan, however, has diverse over-wintering stages – non-diapausing larvae, diapausing larvae, and diapausing adults, whereas in a cooler region, it over-winters only as the final instar larva or adult in diapause.
2. The geographical pattern of over-wintering stages in 12 populations was investigated over a wide range along the mainland of Japan. It revealed that a distinct geographical pattern of over-wintering stages exists in relation to temperature conditions. In regions with warmer climates, the proportion of non-diapausing larvae increased and B. dorsalis had a more complex over-wintering stage structure.
3. Life cycles were also compared between two areas of Japan by field experiments. In the cooler area, the first generation over-wintered in the diapausing larval or adult stage. Conversely, in the warmer area, diapause was induced later and some of the first-generation adults produced second-generation offspring before over-wintering.
4. Based on the geographical cline of climates and the differences in cold hardiness among stages, we can demonstrate that the over-wintering stage variation among and within populations results from an adaptive timing of diapause induction in each region, because the late larval or adult diapauses protect pupae or eggs – which unlike other stages are not cold hardy – from being produced late in the season.     

SORBITOL IN THE EGGS OF THE SILKWORM, BOMBYX MORI

Sorbitol was found to be a normal and sole monosaccharide demonstrable in the late ovarian and in the early embryonic stages of the silkworm, Bombyx mori. This observation was first made on a line of non-diapausing polyvoltine Katsumata strain, but was later confirmed by the analysis of two other Katsumata lines and on several polyvoltine or bivoltine strains. The identification of the sugar extracted from the diapause eggs of a bivoltine strain and from the non-diapausing eggs of a Katsumata strain was based on analyses involving paper chromatography, paper electrophoresis and sorbitol dehydrogenase.     

Seasonal butterfly design: morphological plasticity among three developmental pathways relative to sex,flight and thermoregulation

The temperate‐zone butterfly Pararge aegeria can use three developmental pathways corresponding to different seasonal cohorts: (1) development with a pupal winter diapause resulting in early spring adults; (2) development with a larval winter diapause resulting in late‐spring adults and (3) direct development resulting in summer or second generation adults. In order to test adaptive predictions, we compared variation in flight‐ and thermoregulation‐related morphology among adult males and females from the three pathways using both field data (i.e. wild‐caught butterflies) and experimental breeding data (i.e. reared under different photoperiod regimes). Morphological patterns among the pathways were largely similar in the field and rearing data. Seasonal patterns differed between the sexes for most traits, including (relative) size measures and wing colour. Our results suggest sex‐related, adaptive seasonal plasticity for morphological traits related to flight behaviour in a multivoltine insect.     

The effect of diapause emergence on the seasonal dynamics of a zooplankton assemblage

1. The role of seasonal phenology in the emergence of zooplankton from diapause in patterns of seasonal abundance in the water column was investigated in Oneida Lake, New York. Replicate emergence traps, placed in contact with the lake sediments at two locations (one at a shallow site and one at a deep site), were monitored between May and August.
2. Although six rotifer taxa showed a clear seasonal succession in the water column throughout the study period, all but one taxon emerged exclusively in spring. Three cladoceran and three calanoid copepod species, also present in the water column throughout the study period, again showed predominantly spring emergence. In contrast, three cyclopoid copepod species had distinct seasonal periods of emergence that corresponded, at least in part, to the timing of abundance peaks in the plankton.
3. These results for a single lake are largely consistent with patterns observed or inferred by other investigators for other lakes: variable dependence of abundance in the plankton on diapause emergence for species with long-lived diapausing eggs (i.e. rotifers, cladocerans and calanoid copepods), and much closer dependence for species with short-lived diapausing immature stages (i.e. cyclopoid copepods).     

A novel trade-off of insect diapause affecting a sequestered chemical defense

Diapause allows insects to temporally avoid conditions that are unfavorable for development and reproduction. However, diapause may incur a cost in the form of reduced metabolic energy reserves, reduced potential fecundity, and missed reproductive opportunities. This study investigated a hitherto ignored consequence of diapause: trade-offs involving sequestered chemical defense. We examined the aristolochic acid defenses of diapausing and non-diapausing pipevine swallowtail butterflies, Battus philenor. Pipevine swallowtail larvae acquire these chemical defenses from their host plants. Butterflies that emerge following pupal diapause have significantly less fat, a female fitness correlate, compared to those that do not diapause. However, butterflies emerging from diapaused pupae are more chemically defended compared to those that have not undergone diapause. Furthermore, non-diapausing butterflies are confronted with older, lower quality host plants on which to oviposit. Thus, a trade-off exists where butterflies may have greater energy reserves at the cost of less chemical defense and sub-optimal food resources for their larvae, or have substantially less energetic reserves with the benefit of greater chemical defense and plentiful larval food resources.     

Population dynamics and diapause response of the springtail pest Sminthurus viridis (Collembola: Sminthuridae) in southeastern Australia

The springtail, Sminthurus viridis (L.) (Collembola: Sminthuridae), is an important agricultural pest across southern Australia. We investigated the seasonal abundance patterns and summer diapause response of S. viridis in southeastern Australia by using field and shadehouse (a greenhouse that offers seedlings shade) experiments. Seasonal activity patterns of S. viridis were largely consistent with previous studies, with the pest active from autumn to spring. In addition, the timing and pattern of the summer-diapausing egg stage was established, with multiple generations probably producing diapause eggs. A strong relationship between soil moisture and temperature with autumn emergence also was observed. These results suggest that S. viridis autumn pest pressure can be predicted and indicate that late-season spraying strategies currently used for a sympatric agricultural pest are unlikely to be as effective against S. viridis.     

The roles of temperature and diapause in the life history of a temperate-zone dragonfly: Argia vivida (Odonata: Coenagrionidae)

Abstract. 1. The life cycle of Argia vivida Hagen generally took longer to complete in the field than was predicted on the basis of the thermal sum accumulated in laboratory rearing.
2. The prediction of a bivoltine life-cycle from geothermal sites with either a constant annual temperature of 26°C or thermal range of 11–31°C was not borne out because the intervention of short-day induced developmental delays in later larval instars extended the life cycle to 1 year.
3. This diapause, which synchronizes adult emergence with favourable summer temperatures, was also present in larvae from sites with annual temperature ranges of 0–33°C and 5–20°C.
4. At these colder sites completion of the life cycle takes 2 and 3 years respectively and dragonflies must be in cold-resistant stages during the winter. A long-day diapause, principally affecting late-instar larvae below a certain size during the summer, achieves this.
5. Large diurnal temperature fluctuations at the 0–33°C site markedly increase the useful thermal energy available to larvae for growth over that predicted by the thermal sum equation.
6. The interaction between the effects of temperatures favourable for growth and day-length-governed diapause, synchronize the emergence of the low-temperature sensitive adult stage of this tropical dragonfly with northern-latitude summers at a variety of habitats.     

Effects of photoperiod, temperature, and host plant age on induction of reproductive diapause and development time in Danaus plexippus

Abstract 1. Diapause induction in monarch butterflies Danaus plexippus was studied using adults captured from the wild in Minnesota and Wisconsin, and individuals reared under outdoor and controlled conditions.
2. Oocyte presence in females and ejaculatory duct mass in males were used to indicate reproductive status.
3. Some wild individuals were in diapause in mid-August, and all males and females were in diapause by late August and early September respectively.
4. Individuals reared under decreasing day lengths and fluctuating temperatures were more likely to be in diapause than were individuals reared under long or short day lengths or constant temperatures.
5. Individuals fed potted old Asclepias curassavica plants were more likely to be in diapause than were those fed potted young host plants; when cuttings of Asclepias syriaca plants from the field or greenhouse pots were used, there was no effect of host plant age.
6. Extremely high temperatures increased the number of day-degrees required for development from egg to adult, while decreasing day lengths and older host plants tended to decrease the number of day-degrees required for development.
7. There appears to be a continuum of reproductive development in monarchs, with gradual declines in mean ejaculatory duct mass and oocyte production during the late summer.
8. None of the experimental treatments led to 100% diapause, and diapause was more likely to occur in monarchs subjected to more than one diapause-inducing cue.     

Host plant defences and voltinism in European butterflies

Abstract.  1. With respect to seasonal availability for herbivores, plants defended by synthesising qualitative compounds differ from those protected by accumulation of quantitative macromolecules, leaf toughness, and low water and/or nutrient content. While the palatability of the former plants remains relatively constant during the season, the palatability of the latter group decreases with leaf age.
2. It was hypothesised that in seasonal temperate environments, quantitative plant defences should restrict the annual numbers of insect generations. To test this hypothesis, European butterflies were used as a model, both non-corrected regressions and tests controlling for phylogeny were carried out, and potentially confounding factors such as body size or occurrence in short-season environments were treated as covariables.
3. Non-phylogenetically controlled regressions corroborated that butterflies feeding on quantitatively protected hosts (woody plants + grasses) form fewer generations than species feeding on qualitatively protected forbs. Plant defences fitted voltinism better than butterfly size, and remained significant even after controlling for short seasons. Using independent contrasts, feeding on woody plants plus grasses, and feeding on woody plants only, predicted fewer generations. These patterns, however, applied exclusively for foliage-feeding species.
4. The association between plant defences and voltinism represents a hitherto overlooked pattern in the ecology of temperate herbivores. It may explain why large insects tend to form fewer generations and feed on structurally complex hosts, and why some species remain monovoltine although they are not restricted by short season.     

Reduced pesticide inputs on cereal field margins: the effects on butterfly abundance

Abstract. 1. On a study farm in Hampshire where large blocks of cereal fields had the pesticide inputs on their headlands experimentally and selectively reduced (the practice known as 'conservation headlands'), numbers of butterflies were monitored over 4 years by using transect counts.
2. Consistently more butterflies were seen flying over field edges sprayed under the conservation headland regime compared to those that were fully sprayed.
3. A comparison of changes in butterfly abundance on the study farm containing conservation headlands with data from the National Butterfly Monitoring Scheme indicated that population increases in some species may result from the use of conservation headlands.
4. The implications of resource provisioning and the potential reduction of spray drift into field-margin habitats are discussed in relation to farmland butterflies.     

An experimental examination of the effects of habitat quality on the dispersal and local abundance of the butterfly Parnassius smintheus

Abstract 1. Nectar flower abundance was manipulated through flower removal, and sex ratio was manipulated by moving individual butterflies within a series of nine alpine meadows. The movement and abundance of the butterfly Parnassius smintheus in the meadows were monitored using mark–release–recapture methods.
2. A total of 937 butterflies, 698 males and 239 females, was captured. There were 223 observed between-meadow movements. Fifty-two per cent of males and 35% of females moved among meadows.
3. The immigration of male butterflies was related positively to nectar flowers, host plant abundance, and female butterflies. Male emigration was not affected by any of the treatments. The number of males captured was related positively to nectar flowers and host plants but not affected by sex ratio. The number of resident male butterflies was greater in meadows containing flowers and was related positively to host plant abundance, but unaffected by sex ratio.
4. Flower removal, sex ratio, and abundance of Sedum had no significant effect on the abundance, movement, or residence time for female butterflies, in part due to small sample size.
5. The fact that males immigrate to higher quality meadows suggests that male butterflies are assessing meadow quality, either by sampling meadows or potentially from a distance using olfactory cues.     

Seasonal regulation of dormancy in Chrysopa carnea (Neuroptera)

In Ithaca, New York, diapause incidence in Chrysopa carnea exceeds 50 per cent among adults emerging between 31 August and 3 September. Apparently, decreasing late summer day lengths, which exceed the stationary critical photoperiod in the laboratory, act on the sensitive stages and induce diapause. Full diapause intensity occurs about 2 weeks after adult emergence; complete winter coloration appears approximately 2 weeks later. Photoperiodic stimili in combination with the geographic strain largely determine diapause depth.Decreasing autumn day lengths decelerate diapause development and maintain diapause until the winter solstice. Subsequently, short day lengths and cold temperatures slow diapause development. In nature, neither long days, increasing day lengths, nor chilling hasten diapause termination. Diapause duration is largely determined by the interaction between inducing photoperiod, maintaining photoperiodic and thermal stimuli, and geographic strain. In Ithaca, diapause ends (all response to photoperiod ceases) between 22 January and 12 March.After diapause ends, the animals retain their diapause characteristics until temperatures exceed 4°C. Post-diapause reproductive development in females requires approximately 100 heat units above 4°C; however, below 8°C mating and oviposition are absent. Although the winter coloration remains, mating occurs within 1 day after transfer from 4 to 24°C. Temperature determines the rate at which the green summer colour returns.     

The causes of seasonal changes in numbers of the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae)

ABSTRACT. 1. Counts of adult Scathophaga stercoraria (L.) on cow pats were made in Houghall, County Durham, in 1964 and 1965.
2. A spring peak of numbers was due to adults (overwintered mainly as pupae or larvae) maturing and going to dung to breed. Numbers then dropped, rising to one or more peaks in late June—early July. In 1964 there was then a summer drop in numbers until late September. In 1965 high numbers persisted in summer associated with cooler, wetter weather. Autumn peaks in both years persisted until severe frosts or snow.
3. Mature adults, developed from eggs laid during the spring peak, form the first generation when breeding in mid-late June. No clear generations can be identified after this, due to eggs being laid daily (females have successive gonotrophic cycles). Changes in adult numbers breeding reflects survival of eggs and newly-hatched larvae 5–6 weeks earlier, and lower survival rates of adults in mid-summer compared with spring and autumn.
4. Adult Scathophaga numbers in vegetation rose as numbers on dung dropped. Females dissected to count ovariole tunica dilatations showed that most flies in vegetation were immature, with some parous flies hunting insects to develop the next batch of eggs.
5. Females on dung were dissected and found to range from immature to seven-parous. Those gravid for the first time were grossly under-represented, possibly due to wider dispersal.
6. It is suggested that seasonal changes in this r-strategist cannot be explained simply in terms of generations nor by the occurrence of adult diapause.     

Effects of submergence by winter floods on diapausing caterpillars of a wetland butterfly, Lycaena dispar batavus

1. The influence of seasonal flooding on wetland insects is understudied, and understanding of a potentially important influence on population dynamics is therefore incomplete. This is of particular consequence because many wetland insect species, including the large copper butterfly, Lycaena dispar batavus , are of conservation interest.
2. Previous studies on the submergence tolerance of diapausing L. d. batavus larvae have been inconclusive. This study investigated the effects of different periods of enforced submergence on overwintering survival, using both fresh and brackish water, and comparing effects on larvae in early and late diapause.
3. Larvae were submerged for up to 84 days, and survival was negatively correlated with submergence period, although periods of up to 28 days did not appear to reduce survival. Water type, i.e. fresh vs. brackish water, and larval stage, i.e. early vs. late diapause, had no significant influence on survival.
4. The relevance of these findings to the population biology and conservation of L. d. batavus is discussed. Further studies on the effects of submergence by seasonal flooding on wetland insect populations are encouraged.     

光周期对三带喙库蚊发育期间体内核酸动态的影响

作者测试了长短光周期处理的三带喙库蚊Culex tritaeniornynchus(Giles)各虫态与滞育及解滞蚊体内RNA与DNA的变化.结果表明:幼虫与蛹核酸含量最高,成虫期变化比较稳定.短光周期可以降低该蚊发育期间核酸的合成作用.雌蚊卵形成期间DNA相对稳定,吸血后卵巢开始发育,RNA含量明显增加,36—48小时达到高峰,然后逐渐下降.10—15日龄的滞育蚊体内DNA比发育蚊低,解滞蚊RNA与DNA含量均比发育蚊为高.新蚊、发育、滞育与解滞蚊间DNA、RNA含量不同,DNA、RNA减少与增加可用作判断滞育发生与解除的一个生化指标.     

中华稻蝗长沙种群的生活史及其卵滞育的进化意义

中华稻蝗Oxya chinensis为重要的水稻害虫,在我国除青海、西藏、新疆、内蒙古等未见报道外,南起海南北至东北均有分布,在许多的分布区域1年发生1代。为探索中华稻蝗长沙种群的生活史及其季节适应特征,通过野外和实验室的研究,调查了其发生代数、孵化率和卵滞育率的季节变化及越冬卵的存活率。结果显示,中华稻蝗长沙种群为1年2代和1年1代混合发生:第1代卵产卵后大部分孵化为若虫而1年完成2代,但亦有19.4% -4.1%的卵不孵化而1年只能完成1世代。第1代成虫于6月上旬至8月上旬羽化,6月下旬至8月中旬产卵;第2代若虫于7月初开始孵化,9-10月羽化为成虫,10月上旬至11月下旬产卵。在室外自然条件下,中华稻蝗长沙种群6-8月(第1代)和10-11月(第2代)所产卵块均为部分滞育,滞育率为30%左右,皆无显著差异。然而,其卵滞育率在12月以后显著降低,仅为6.6%或以下,卵滞育快速地得以解除。因此,包括非滞育卵和滞育解除卵,中华稻蝗长沙种群的越冬卵皆以非滞育状态度过其后的寒冷季节。即使是遭遇长江流域2007年末至 2008年初异常寒冷的冬季,在长沙地区越冬后其卵的存活率亦在98%以上。非滞育状态的中华稻蝗长沙种群越冬卵完全能安全地越冬,其滞育的发生并非是为了提高其耐寒性而安全度过不适环境。并探讨了中华稻蝗长沙种群卵滞育的进化意义。     

Asymmetric life-history decision-making in butterfly larvae

In temperate environments, insects appearing in several generations in the growth season typically have to decide during the larval period whether to develop into adulthood, or to postpone adult emergence until next season by entering a species-specific diapause stage. This decision is typically guided by environmental cues experienced during development. An early decision makes it possible to adjust growth rate, which would allow the growing larva to respond to time stress involved in direct development, whereas a last-minute decision would instead allow the larva to use up-to-date information about which developmental pathway is the most favourable under the current circumstances. We study the timing of the larval pathway decision-making between entering pupal winter diapause and direct development in three distantly related butterflies (Pieris napi, Araschnia levana and Pararge aegeria). We pinpoint the timing of the larval diapause decision by transferring larvae from first to last instars from long daylength (inducing direct development) to short daylength conditions (inducing diapause), and vice versa. Results show that the pathway decision is typically made in the late instars in all three species, and that the ability to switch developmental pathway late in juvenile life is conditional; larvae more freely switched from diapause to direct development than in the opposite direction. We contend that this asymmetry is influenced by the additional physiological preparations needed to survive the long and cold winter period, and that the reluctance to make a late decision to enter diapause has the potential to be a general trait among temperate insects.