The Life Cycle of Lestes viridis (Odonata: Lestidae) in Two Seasonal Streams of the Sierra Morena Mountains (Southern Spain)

The life cycle of the zygopteran odonate Lestes viridis in two seasonal streams in the Sierra Morena Mountains is inferred from size-frequency analyses of handnet samples of larvae and records of presence and reproductive activity of adults during three consecutive years. The egg stage (duration 5–6 months) overwinters, larval development is brief (6–8 weeks) and adults undergo a protracted, prereproductive, summer diapause (up to 3 months) before mating and ovipositing in late September, about one week after the first appreciable fall of rain, but before surface water reappears in the streams after having been absent for about four months during the hot, dry summer. Comparison between this life cycle and those of more northerly populations reveals a latitude-correlated cline in phenology resembling that found in some other northern hemisphere odonates that, like L. viridis, maintain an obligatorily univoltine life cycle at different latitudes.     

大田淹水对夏玉米叶片衰老特性的影响

选用登海605(DH605)和郑单958(ZD958)为试验材料,在大田条件下研究了不同淹水时期(三叶期、拔节期和开花后10 d)和持续时间(3 d、6 d)淹水对夏玉米叶片衰老特性的影响.研究表明: 淹水胁迫后超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)等保护酶活性以及可溶性蛋白含量较不淹水对照显著下降,而丙二醛(MDA)含量显著升高,三叶期淹水6 d后DH605和ZD958的含量较对照分别升高35.3%和34.1%.淹水胁迫后叶片叶绿素含量降低,产量显著下降.三叶期淹水6 d对夏玉米产量的影响最大,DH605和ZD958较对照分别减产32.1%和35.2%.不同生育期中,三叶期淹水造成的影响最大,拔节期次之,开花后10 d淹水造成的影响较小,且影响程度随淹水持续时间的延长而加剧.     

Responses to olfactory and visual cues by over-wintered and summer generations of the pollen beetle, Meligethes aeneus

Abstract.  Behavioural responses to odours of oilseed rape in bud and flower stage and to green and yellow colours are studied for the two main phenological stages of pollen beetles, Meligethes aeneus , a major pest of oilseed rape, Brassica napus . Over-wintered individuals oviposit in buds of oilseed rape. Adults of the new generation (i.e. the summer generation) feed on flowers of different plant species before over wintering. In olfactometer experiments, the over-wintered beetles display a higher preference for odour of oilseed rape at the bud stage compared with the summer generation, both with and without colour stimuli. Flower odours are preferred in combination with yellow colour. Colour stimuli presented alone do not affect the behaviour. The summer generation beetles respond to both bud and flower odour. Adding colour stimuli changes the summer generations preference towards yellow and flower odour.     

A Note on Abiotic Factors that Constrain Periphyton Growth in Alpine Glacier Streams

Periphyton growth limitation experiments were conducted in five glacier streams during the main ice melt period in late summer using nutrient diffusing substrata (NDS) that contained nitrate and/or phosphate. Periphyton net growth was determined as chlorophyll a accrual after an exposure time of 4 weeks. In addition, primary water chemistry and physical parameters of the study streams were measured. These chemical and physical parameters characterised the sites as kryal (glacial) systems. Neither nutrient limitation nor a significant correlation between water chemistry and physical data and chlorophyll a values were apparent. A comparison between current velocity and ln‐transformed chlorophyll a values revealed a typical optimum curve with highest periphyton accrual at 0.5 m s^–1 on NDS. During the summer ablation period, the net growth of periphyton in these glacial streams appeared to be controlled primarily by current velocity.     

Genetic basis of photoperiodic control of summer and winter diapause in geographic ecotypes of the rice stem maggot, Chlorops oryzae

Chlorops oryzae Matsumura (Diptera: Chloropidae) is bivoltine in northern Japan but trivoltine in the southern part of the country. Larvae of the bivoltine strain (Akita, 39° N) develop without delay under L14:D10 but enter summer diapause in the mature larval stage under L15:D9. In contrast, larvae of the trivoltine strain (Aichi, 35° N) develop quickly under L15:D9 but enter summer diapause under L14:D10. The genetic basis of their different summer-diapause behavior was analyzed by reciprocal crossing between the two ecotypes and backcrossing to the hybrids. Although a polygenic system seems to be involved, there is a single gene on the X-chromosome exerting a major effect on summer diapause. The northern bivoltine ecotype has a longer critical photoperiod for the induction of winter diapause in the first larval stage and remains in diapause longer than the southern trivoltine ecotype. The differences in the critical photoperiod and the winter diapause duration between the two ecotypes seem to be controlled by a polygenic system but again a sex-linked or closely linked gene (or genes) plays a major role. The two geographic ecotypes differ significantly in summer- and winter-diapause traits, both of which are characterized by sex-linked inheritance. Despite this, no apparent sterility or inviability in hybrids between the ecotypes occurs.     

Analysis of larval antigens of Oestrus ovis for the diagnosis of oestrosis by enzyme-linked immunosorbent assay

A serodiagnostic test for the diagnosis of infestation by the sheep nasal bot fly, Oestrus ovis (Linné) was examined. The enzyme-linked immunosorbent assay (ELISA) technique was used to analyze and compare the production of immunoglobulin G (IgG) antibodies against excretory-secretory products (ESP) and crude extract (CE) antigens from all the different larval stages of O. ovis in the sera of 276 adult sheep sampled in summer (n = 135) and winter (n = 141). ESP from first stage larvae was the most sensitive, coating antigen in winter and ESP from second stage larvae during summer. The most specific values were obtained by ESP against L1 in winter and by CE against L3 in summer. These results show that the stage of larval development has a significant impact on the humoral immune response over the course of a season. A significant correlation (P < 0.001) was found between the number of O. ovis larvae and the serum antibody levels using all differents antigens, except L3 CE. In Spain, where a long favourable period exists for the evolution and development of the different stage larvae between March and November, the ELISA test using L1 ESP antigen during winter and L2 ESP antigen in summer may be used for ovine oestrosis immunodiagnosis.     

气候变化背景下中国南方地区季节性干旱特征与适应Ⅳ.基于作物水分亏缺指数的玉米干旱时空特征

基于1959－2008年中国南方地区249个气象台站的地面观测资料,以作物水分亏缺指数为玉米干旱指标,计算其干旱频率和干旱站次比,分析中国南方地区春玉米和夏玉米各生育阶段发生干旱的时空分布特征.结果表明: 从干旱发生频率的空间分布看,春玉米在淮北、云南北部和华南南部发生的干旱较严重,在其他地区的干旱相对较轻;除了长江中下游地区、华南北部和西南东部的夏玉米在生育后期干旱较严重,研究区域内夏玉米在其生育前期和中期干旱较轻.从干旱面积和强度的变化趋势看,长江中下游地区春玉米在七叶到拔节阶段的干旱强度明显增加,在吐丝后到乳熟阶段的干旱面积和强度呈减小趋势;夏玉米在拔节后期到抽雄阶段以及吐丝后到乳熟阶段的干旱都呈减轻趋势.西南地区春玉米、夏玉米的干旱强度和范围没有明显趋势.从干旱面积和范围的年际和年代际变化看,长江中下游地区夏玉米的变化较大,而西南地区差异较小.     

Leaf Litter as a Source of Dissolved Organic Carbon in Streams

Dissolved organic carbon (DOC) is an abundant form of organic matter in stream ecosystems. Most research has focused on the watershed as the source of DOC in streams, but DOC also comes from leaching of organic matter stored in the stream channel. We used a whole-ecosystem experimental approach to assess the significance of leaching of organic matter in the channel as a source of DOC in a headwater stream. Inputs of leaf litter were excluded from a forested Appalachian headwater stream for 3 years. Stream-water concentration, export, and instream generation of DOC were reduced in the litter-excluded stream as compared with a nearby untreated reference stream. The proportion of high molecular weight (HMW) DOC (more than 10,000 daltons) in stream water was not altered by litter exclusion. Mean DOC concentration in stream water was directly related to benthic leaf-litter standing stock. Instream generation of DOC from leaf litter stored in the stream channel contributes approximately 30% of daily DOC exports in this forested headwater stream. This source of DOC is greatest during autumn and winter and least during spring and summer. It is higher during increasing discharge than during base flow. We conclude that elimination of litter inputs from a forested headwater stream has altered the biogeochemistry of DOC in this ecosystem. Received 2 September 1997; accepted 27 January 1998.     

三峡正常蓄水后长江口叶绿素a和溶解氧变化及其成因

根据2010年8月、10月和2011年5月的现场监测数据,对长江口水域在三峡水库175m试验蓄水实施后一个水文年中叶绿素a和溶解氧(DO)的分布特征及其影响因素进行分析。结果表明,叶绿素a平面分布夏季有两个高值中心,春季有一个高值中心;在口门北缘夏季表层叶绿素浓度值最高。垂向上,夏季叶绿素a浓度表层和底层高;春季和秋季叶绿素a浓度中层高。夏季表层和底层DO浓度相差较大,秋季和春季表、底层DO浓度分布比较均匀;整体上秋季和春季的DO浓度高于夏季。工程蓄水后DO低值区和叶绿素a峰值区向口门内位移,对生态系统结构将产生影响。     

sh-2超甜玉米乳熟期籽粒重量和碳水化合物变化及与温度降雨量的回归分析

采用夏季不同播期,研究了sh-2型超甜玉米乳熟期籽粒重量和碳水化合物的变化,用多重回归分析方法对气温、降雨量与籽粒重量、碳水化合物含量的关系进行了分析．结果表明,两个播期的可溶性总糖、果糖、蔗糖含量变化趋势有明显差异．夏季早播,提高了乳熟期籽粒鲜重和干重,灌浆速率,可溶性总糖和淀粉含量．说明夏季早播有利于提高甜玉米的独特甜风味和产量构成．移栽-收获期的T（温差）、K（有效积温）和RF（降雨量）是影响乳熟期籽粒鲜重和干重及可溶性总糖、果糖、蔗糖、淀粉含量的主要因子,K、RF表现正相关效应;在授粉-收获期,K是影响的主要因子,K与籽粒鲜重和干重及果糖、淀粉含量呈正相关,与籽粒蔗糖含量呈负相关．     

Distribution and Ecology of Campylobacters in Coastal Plain Streams (Georgia, United States of America)

Campylobacter is the leading cause of bacterium-associated diarrhea in the United States and most developed countries. While this disease is considered a food-borne disease, many clinical cases cannot be linked to a food source. In rural and agrarian areas environmental transmission may be an important factor contributing to case loads. Here we investigated the waterborne prevalence of campylobacters in a mixed-use rural watershed in the coastal plain of southern Georgia (United States). Six sites representing various degrees of agricultural and human influence were surveyed biweekly to monthly for 1 year for the presence of culturable thermophilic campylobacters and other measures of water quality. Campylobacters were frequently present in agriculture- and sewage-impacted stretches of streams. The mean campylobacter counts and overall prevalence were highest downstream from a wastewater treatment plant that handled both human and poultry slaughterhouse waste (≤595 CFU ml⁻¹; 100% positive); the concentrations were significantly higher than those for the four upstream sites (P < 0.05). The counts were significantly correlated with the number of fecal coliform bacteria, conductivity, pH, and concentrations of nutrients (NO₃⁻, PO₄³⁻, and NH₃). Campylobacters were isolated more frequently and larger numbers were present during the summer months, similar to the occurrence of clinical cases of campylobacteriosis in this region. A multivariate model showed that the levels were significantly influenced by increasing precipitation, which also peaked in the summer. The results indicate that loading from both human and domestic animal waste may be high in the watershed studied during the summer months. Mixed-use watersheds supporting agriculture production, human populations, and wildlife may be at risk for contamination by campylobacters and may be an important route for human exposure.     

The bionomics of the free-living larvae and the transmission of Dictyocaulus filaria between lambs in North-East England.

The bionomics of the free-living larvae of Dictyocaulus filaria on pasture, and the transmission of infection between lambs, were studied during different seasons of the year in North-East England. The rate of development of first-stage larvae to the third stage took 4-9 days in late spring and summer, 1 1/2-4 weeks in autumn and 5 1/2-7 weeks in winter. The proportion of first-stage larvae developing to the third stage ranged from 10-28% in autumn and winter, and 2-25% in spring and summer. The rate of mortality of the third-stage larvae was approximately logarithmic in nature, although the survival time was shorter in spring and summer than in autumn and winter. Third stage larvae were able to survive from autumn until the spring of the following year in sufficient numbers to perpetuate transmission but not to cause clinical disease. In a transmission study, the survival of the infective larvae on the experimental plot was poor in summer, but the larval population increased in the autumn and then declined slowly throughout the winter. Infection in the susceptible lambs was related to the level of infection on the herbage increasing in severity from early summer to late autumn. However, those lambs infected in the summer were resistant to the heavy autumn challenge of larvae on pasture.     

The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle,Colaphellus bowringi (Coleoptera: Chrysomelidae)

The cabbage beetle, Colaphellus bowringi, is a short-day species undergoing an imaginal summer and winter diapause. Its photoperiodic response highly depends on temperature. All adults entered diapause at ≤ 20 °C regardless of photoperiods. High temperatures strongly weakened the diapause-inducing effects of long daylengths. The diapause-averting influence of short daylengths was expressed only at high temperatures (above 20 °C). This indicates that the beetle has a cryptic ability to reproduce in summer. In fact, summer and winter diapause were induced principally by relatively low temperatures in the field, whereas photoperiod had less influence on diapause induction. The critical daylength for the autumnal population was between 12 h and 13 h. By transferring from a long day to a short day or vice versa at different times after hatching, it was shown that the sensitive stage with regard to photoperiod was the larva, whereas a long day was photoperiodically more potent than a short day. The sensitive stage to temperature encompassed the larval, pupal and adult stages. This different response pattern serves to ensure that the beetle enters summer and winter diapause in time. The selections for non-diapause trait under laboratory (at 25 °C) and natural conditions (at >24 °C) showed that the beetle could lose its sensitivity to photoperiod very rapidly.     

Leachates of Eucalyptus globulus in Intermittent Streams Affect Water Parameters and Invertebrates

Low order streams running through Eucalyptus globulus plantations in Central Portugal are frequently reduced to isolated permanent or temporary summer pools with darkly stained water due to leaf leachates. Here we assess the toxicity of such leachates to the shredder Sericostoma vittatum. Leachates resulted in deoxygenated and more acid water, and increased its phenolic content and conductivity. S. vittatum exposed to high concentrations of leachates failed to grow and died within 30 days even in the presence of high quality food. Larvae in water with half the leachate concentration, consumed less leaf material, had lower growth rates, did not pupate and died within 100 days. Eucalypt leachates per se may affect the viability and ecology of macroinvertebrates in Portuguese streams. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Seasonality and life cycles of woody plant-feeding noctuid moths (Lepidoptera: Noctuidae) in Mediterranean habitats

Abstract.

• 1 The annual cycle of noctuid moths feeding as larvae on the foliage of eighteen woody plant species (belonging to ten different families) was studied at two southeastern Spanish Mediterranean forest habitats. Two questions were addressed in this study. (1) Does the rigorous (hot and dry) summer season characteristic of the Mediterranean-type climate impose a constraint on noctuid life histories? (2) Are there detectable differences in abundance or phenological patterns between the noctuid assemblages feeding on evergreen and winter-deciduous trees and shrubs?
• 2 Regardless of their leaf persistence habit, the majority of woody species studied had short shoot growth and leaf production periods in spring. Abundance of noctuid larvae peaked in May-June, shortly after host plants started to produce new leaves. Virtually no noctuid larvae were found on the foliage of the woody species studied at other times of year. Abundance and seasonal pattern of occurrence of larvae were similar on evergreen and deciduous food plants.
• 3 In contrast with the unimodal seasonal pattern exhibited by larvae, the abundance of adult moths (assessed by light trapping) showed two distinct peaks in early summer and early autumn, and a marked minimum in mid-summer.
• 4 Most woody plant-feeding noctuids recorded in this study (86% of species, about 95% of individuals) were univoltine. Univoltine species fell into one of two distinct life history categories, corresponding to pre- and post-summer flight periods. These two contrasting phenologies were associated with a bimodality in the duration of the pupal stage (‘short’ versus ‘long’), and were closely related to taxonomical affiliation at the subfamily level.
• 5 Within the ‘short’ pupal duration group, some species mate and oviposit shortly after emergence and pass the dry season in the egg stage, while others remain as potentially active, non-reproductive adults over most of the summer and mate by the end of that season. Species in the ‘long’ pupal duration group pass the summer in pupal or prepupal stage.
• 6 In the Mediterranean habitats studied, the adversity of the summer dry season seems to have led to a woody plant-feeding noctuid species assemblage almost entirely made up of univoltine species that concentrate their larval phases when suitable food (young leaves) is most abundant, and ‘avoid’ mid-summer as a flight time by emerging either shortly before or shortly after the adverse summer drought period. Year-round foliage availability afforded by dominant evergreen plants does not seem to have influenced the seasonal organization of noctuid cycles in any substantial way.

     

The effect of weather on the life cycle of the speckled wood butterfly Pararge aegeria

ABSTRACT.

• 1 Pararge aegeria (L.) is a very unusual butterfly of Britain, having a long period of adult activity, from April to October, without discrete flight periods. In central Britain it overwinters in two stages: pupae and third instar larvae, both being the progeny of late summer adults. Other larval stages die at the onset of cold winter weather. The overwintering stages give rise to the first adult generation in spring, split into two parts.
• 2 Different temperature regimes affect development rates in larvae and pupae differently. Late larval development is more rapid than that of pupae at low temperatures, thus in cool spring weather the overlap of the two parts of the first generation is greater than in warm spring weather.
• 3 Adults emerge continuously throughout the summer because larval development rates are variable. When summer is warm there is a partial third generation but when cool only two.
• 4 The timing of the end of the flight period is consistent with the hypothesis that both temperature and photoperiod are important in determining whether individuals enter diapause or develop directly. In warm summers larvae develop beyond a sensitive stage before critical daylength is reached and develop directly, but in cool summers individuals enter diapause because they are at the sensitive stage when critical daylength is reached.
• 5 It is suggested that variable development rates can facilitate parasite escape in autumn and increase the probability of adult success when weather is unpredictable, and this strategy is maintained because these benefits are greater than the cost of winter mortality of larvae.

     

The effects of season and moderate nutritional restriction on ovarian function and oocyte nuclear maturation in cycling gilts

The fertility of female pigs is impaired during summer and in response to restriction of feed intake, resulting in reduced productivity of the breeding herd. This study determined the effect of season and moderate nutritional restriction on ovarian function and oocyte developmental competence of cycling gilts. Eighty prepubescent gilts were used across two seasons—summer (S: January to March) and winter (W: June to August)—and received either a high (2.5× maintenance) or a moderately restricted (1.5× maintenance) feeding level for the first 19 days of their second estrous cycle. On Day 19, ovaries were collected post-slaughter. Diameters of all surface follicles over 1 mm were measured. All follicles ≥4 mm were aspirated and cumulus–oocyte complexes underwent in vitro maturation for ∼44 hours to assess oocyte developmental competence on the basis of metaphase II (MII) attainment. Moderate dietary nutrition reduced daily liveweight gain but did not affect the ovarian follicle population or oocyte developmental competence. The number of large follicles (≥6 mm) was lower during summer (S: 10.7 ± 1.74 vs. W: 15.5 ± 1.15, P < 0.05), as was the proportion of oocytes at the germinal vesicle stage of meiosis (S: 0.06 ± 0.02 vs. W: 0.08 ± 0.02, P < 0.05). However, the proportion of oocytes attaining MII was similar in summer and winter (S: 0.72 ± 0.04 and W: 0.69 ± 0.06, P > 0.05). Intrafollicular concentrations of luteinizing hormone were higher in summer (S: 43.05 ± 6.44 vs. W: 12.05 ± 5.12 ng/mL, P < 0.001), whereas estradiol was lower (S: 1.27 ± 0.36 vs. W: 27.52 ± 5.59 ng/mL, P < 0.001). In conclusion, our data demonstrated that in summer, follicle growth beyond 6 mm is impaired during the periovulatory period, without affecting oocyte meiotic competence. Importantly, these data also demonstrated that ovarian follicle growth and the capacity of oocytes to reach MII in vitro appear unaffected by moderate nutritional restriction during the preceding estrous cycle.     

The decomposition of mangrove litter in a subtropical mangrove forest

Decomposition of Avicennia marina (Forsk.) Vierh. leaf and woody litter (twigs) was studied using litter bag experiments in a subtropical mangrove forest at two tidal levels (high and low) with different inundation regimes and during two seasons (summer and winter). Losses in dry weight were best described by a single exponential model which showed loss rates of both leaves and twigs were significantly higher low down on the shoreline (greater inundation) and in summer. The time (days) required for the loss of half of the initial dry weight (t ₅₀) was summer: high 59, low 44; winter: high 98, low 78. For twigs the values (days) were summer: high 383, low 179; winter; high 1327, low 1207. There is an exponential relationship between leaf litter t ₅₀'s and latitude which indicates the importance of temperature and therefore season, to the dynamics of organic cycling and export in mangrove systems.     

Comparing the Fish and Benthic Macroinvertebrate Diversity of Restored Urban Streams to Reference Streams

Urbanization is associated with substantial losses to stream biological diversity throughout the United States' mid‐Atlantic. Stream restoration has been used to improve stream conditions and, in part, to ameliorate these losses. However, the relationship between restoration and recovery of biological diversity is unclear. Our objective was to critically examine the efficacy of urban stream restorations with regard to biological diversity. We compared restored urban streams to urban nonrestored, nonurban, and reference (minimally degraded) streams using five measures each of fish and benthic macroinvertebrate diversity. Both multivariate and univariate statistical analyses show biological diversity of restored urban streams to be similar to nonrestored urban streams and lower than nonurban and reference streams. Restored urban sites showed no apparent increase in biological diversity through time, while diversity decreased at two of the reference streams coincident with increased urban development within their catchments. Our results indicate that restoration approaches commonly used regionally as in these urban streams are not leading to recovery of native stream biodiversity. Evidence from several sources indicates a need for dramatic changes in restoration approach, and we argue for a watershed‐scale focus including protection of the least impacted streams and adopting other land‐based actions within the watershed where possible.