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1.
Agapetus fuscipes is a caddisfly that only seems to occur in unimpacted streams and therefore can be a suitable indicator species for natural conditions. The species has decreased in the Netherlands because of human activities which caused organic pollution and hydromorphological degradation. Literature was reviewed to study the autecology and life cycle of A. fuscipes in order to reveal the ecological requirements of this species. By taking Agapetus fuscipes as an example, it is shown that the autecology and life cycle of an indicator species can give important clues for its presence in unimpacted and absence in impacted streams. A. fuscipes is very susceptible to organic pollution and to a lesser degree to discharge dynamics (dropping water level and discharge peaks). The species copes with dynamic discharge events by maintaining a high population density and recolonisation of disturbed habitats from refuges. However, the vulnerability of the species strongly depends on the life stage of the animals (e.g., the ability to migrate, the oxygen demand and the habitat requirements differ between instars). Although several adaptations to dynamic conditions, a high frequency of discharge peaks or a long period of drought can cause the population to decline. Once a population has totally disappeared from a stream it will take the species a long time to recolonise the stream because of its low dispersion capacity. To protect this species stream restoration should focus on water quality (avoid organic pollution and agricultural run off) and on stabilising the discharge by taking care of natural infiltration in the catchment area instead of fast removal of rain water by drainage systems. 相似文献
2.
As a contribution to the long-term emergence studies carried out as part of the “Breitenbach ecosystem project”, this paper presents the results obtained on emergence patterns and population dynamics of blackflies from 1984 to 1988. The Breitenbach is a small first order stream near Schlitz/Hesse, running into the Fulda river. Adult blackflies were caught in 4 greenhouse emergence traps, each spanning the whole width of the stream for a length of 6 m. A manual and then a partly automated method for collecting trapped insects was applied for three years and one year, respectively. Sixteen blackfly-species of different origin were found in the traps: a) autochthonous species: Prosimulium tomosvaryi, Simulium vernum s.l., S. cryophilum s.l., S. ornatum s.l. (common); S. costatum, S. trifasciatum, S. monticola, S. argyreatum (rare); b) species of doubtful origin: S. lundstromi, S. angustitarse, S. angustipes, S. aureum (very rare); c) allochthonous species: S. lineatum, S. equinum, S. erythrocephalum, S. noelleri. It was shown that the last 4 species had not emerged from the Breitenbach but had flown into the traps as adults. In addition, females of autochthonous species with blood or with mature eggs were trapped, which were also considered to have flown in. Besides revealing a limitation of the trap construction, they supported the detailed interpretation of some intricated patterns of appearance. Variations in emergence patterns and specimen numbers between years and traps were pronounced, but only in a few cases could they be attributed to changes in abiotic factors such as water temperature or discharge. P. tomosvaryi had the most simple and regular life cycle, with one well synchronised emergence peak annually from April to May (or even to June). No gradient of specimen numbers along the stream was evident. The two closely related species S. vernum and S. cryophilum had quite similar emergence patterns: There were two broad peaks per year, extending mainly from March to June and from July to October or November. In some cases the number and separation of consecutive generations was not clear. The abundance of both species clearly decreased downstream, more so for S. cryophilum than for S. vernum. In a trap closest to a tributary spring, S. cryophilum was the dominant species during three of the four years examined. The adults of S. ornatum displayed an intricate pattern of appearance, with very low specimen numbers in spring and medium to very high numbers in July/August and September/October. S. ornatum is the only blackfly species that inhabits both the Breitenbach and the adjacent section of the Fulda river. It was shown that females emerging from the Fulda river regularly invade the Breitenbach valley in greatly varying numbers and oviposit there. This leads to overlapping larval cohorts with corresponding emergence peaks. Although S. ornatum was the most abundant species in one year in the lower traps (60 to 80% of all individuals), it remains uncertain whether it is a long-term, permanent member of the autochthonous blackfly fauna of the Breitenbach. Estimates of total numbers of flown-in adults, actual emergence, dry weight biomass, the ecological separation of the species and their life cycle strategies are discussed. 相似文献
3.
Johann Waringer Wolfram Graf Thomas Pitsch Steffen U. Pauls Ana Previši? Mladen Ku?ini? 《Limnologica》2011,41(3):249-255
In the Swiss Jura adults of Drusus mixtus and unknown Drusinae larvae which could not be identified with existing keys were sampled. Based on ripe pupae, the unknown larvae were identified as D. mixtus. The association was confirmed by specimen rearing in aquaria.Based on morphology, larvae of D. mixtus key out together with Drusus croaticus in existing keys. D. mixtus is separated from the latter species by the shape of the anteromedian metanotal sclerites which are broadly triangular, whereas in D. croaticus the sclerites are almost parallel-sided, resembling a stretched rectangle. In addition, the two species are geographically well separated: D. croaticus is restricted to the confines of Croatia and Slovenia, whereas D. mixtus is only present in Switzerland and eastern France. With this present paper, all Central European Drusinae species except Drusus chapmani McL, 1901, (France, Switzerland) and D. noricus Malicky, 1981, an endemic from the Saualpe (Carinthia, Austria), are known in the larval stage. 相似文献
4.
Caddisfly (Trichoptera) larvae are an abundant and widespread aquatic insect group characterized by the construction of silk structures, including nets and cases. Case-building caddisfly have the potential to modify the sorting and mobility of sand and fine gravel via: (1) case construction, resulting in altered sediment properties; (2) transporting sediment incorporated into cases over the river bed; and (3) changing the structure of river beds via burrowing activity. To investigate these mechanisms, it is necessary to understand the mass, size distribution and spatial variability of sediment use by case-building caddisfly larvae. We quantified the mineral sediment used by individuals and communities of case-building caddisfly in 27 samples, from three sites on a gravel-bed stream. The mass and size distribution of sediment in individual cases varied between taxa (mass = 0.001–0.83 g, D50 = 0.17–4 mm). The mean mass of sediment used by the caddisfly community was 38 g m−2 and varied locally. Sediment use was predominantly coarse sand (D50 = 1 mm). 64% of sediment use was attributable to Agapetus fuscipes (Glossosomatidae). Due to within-species variability in case mass, the abundance of most taxa, including A. fuscipes, was only weakly associated with the mass of sediment used by this species, at the river scale. Whilst the caddisfly community used a small percentage of the total sediment available (average 2.99% of the 1–1.4 mm size fraction), A. fuscipes used more fine sediment in their cases at sites where it was more available. Despite variability in local habitat, all sites supported diverse case-building caddisfly communities utilizing mineral sediment. Consequently, geomorphological effects of case-building caddisfly are potentially widespread. The results provide novel insights into the specific grain sizes and quantities of fine sediment used by caddisfly larvae, which represents an important step towards understanding their zoogeomorphic activities. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. 相似文献
5.
Johann Waringer Wolfram Graf Steffen U. Pauls Heinrich Vicentini Verena Lubini 《Limnologica》2008,38(1):34-42
At three alpine locations in Switzerland adults of Drusus melanchaetes and unknown Drusinae larvae which could not be identified with existing keys were sampled. Based on DNA association with adults, we identified the unknown larvae as D. melanchaetes. To further support the association of specimens a phylogeny was estimated with the putative closest relatives of D. melanchaetes – D. monticola and D. nigrescens – and five other species of Drusus (D. chrysotus, destitutus, discolor, muelleri and romanicus). A highly supported monophyletic clade groups unknown larvae and D. melanchaetes specimens from the central Alps and Austria (Vorarlberg), confirming the association.Based on morphology, larvae of D. melanchaetes key out together with D. destitutus in existing keys. D. melanchaetes is separated from the latter species by the shape of the lateral head profile which is almost straight and shows a small step at the height of the antenna, whereas in D. destitutus the lateral head profile is evenly rounded. In addition, in frontal view, the shape of the lateral head outline is straight in D. melanchaetes and rounded in D. destititus. There are also differences in the shape of the pronotum and in the number of the posterodorsal setae at the eighth abdominal dorsum. 相似文献
6.
Macroinvertebrates play a key role in lotic ecosystems, as fish prey and processors of organic material. Therefore, their hydraulic preferences have to be integrated in instream habitat models for ecological stream management. This study characterized physical habitat use in terms of shear velocity for the larvae of three Ephemeropteran (Ephoron virgo, Oligoneuriella rhenana, and Serratella ignita), two Trichopteran (Cheumatopsyche lepida and Hydropsyche exocellata) and one Dipteran species (Blepharicera fasciata) in a Mediterranean stream at a relatively low water discharge. O. rhenana, C. lepida, H. exocellata, and B. fasciata larvae were mainly found in high shear velocity conditions, whereas E. virgo and S. ignita larvae were found in low shear velocity conditions. Knowing that habitat preferences should vary during ontogenesis (with respect to changes in biological requirements and/or morphological abilities to withstand high flow, for example), our second objective was to characterize differences in the hydraulic habitat use (in terms of shear velocity) for different size classes of these six species.Larvae of H. exocellata and B. fasciata mainly colonized high shear velocity conditions and numerous individuals of these species also used medium shear velocity conditions, independent of size class.The use of high shear velocity conditions increased with larval size for C. lepida and O. rhenana, whilst the use of low shear velocity conditions increased for larger larvae of E. virgo and S. ignita. Various hypotheses are proposed to explain these different strategies of habitat use during ontogenesis. We point out the lack of knowledge about physical habitat shifts during the larval growth of freshwater invertebrates.These results highlight the interest to consider the respective habitat requirements of different size classes of invertebrates in instream habitat models. Population bottlenecks should be overcome if hydraulic conditions are kept suitable for all size classes by stream managers. 相似文献
7.
珠江干流长洲水利枢纽蓄水后珠江鳡鱼(Elopichthys bambusa)早期资源现状 总被引：1，自引：0，他引：1
长洲水利枢纽是珠江干流最下游一级的梯级水坝,其正常蓄水后必然改变下游的水文环境特征,也必将对下游的鳡鱼产卵场功能造成一定的影响.为了解长洲水利枢纽蓄水后珠江鱤鱼(Elopichthys bambusa)的资源现状,2008 2013年在珠江肇庆江段设立固定采样点,通过定量弶网对鳡鱼早期补充群体进行调查.结果显示:珠江鳡鱼苗主要出现在4月中旬至8月上旬,多年平均持续时间为97±21 d,盛期在5 7月,鳡鱼苗占鱼苗早期补充群体总量的0.46%±0.21%.鳡鱼苗的出现具有明显的季节变化规律,每年伴随洪峰有3~5次苗汛出现,苗汛次数与洪峰次数之间存在显著相关关系,但苗汛峰值大小与径流量之间不存在显著相关关系.鳡鱼苗多年平均资源量为16.89×108±9.16×108尾,繁殖群体总量约为52.8 t.研究表明:长洲水利枢纽蓄水后鳡鱼早期资源量呈下降趋势,但珠江禁渔缓解了长洲水利枢纽建设对珠江鳡鱼资源的影响.基于以上结果,为长洲水利枢纽蓄水后珠江鳡鱼的保护提出了建议. 相似文献
8.
A total of 1504 larval and 31 pupal Simuliidae were caught from March 2000 to February 2001 at the Weidlingbach, a fourth order tributary of the Danube near Vienna, Austria, using a modified box sampler (sampling area = 2116 cm2) at 12 sampling stations from source to mouth. From the six species collected, Prosimulium tomosvaryi (Enderlein) and two species of the Simulium ornatum-group (S. trifasciatum Curtis and S. ornatum Meigen) accounted for 97.5% of the total. Based on head width, instars 1–7 were collected in the S. ornatum-group and instars 2–7 in P. tomosvaryi; from two of the remaining species [Simulium (Nevermannia) cryophilum (Rubzov) and S. (N.) vernum Macquart], only pupae were sampled. The S. ornatum-group was most abundant on coarse substrates (median = 55.9 mm) exposed to high water velocity (median = 55.9 cm/s; range = 9–83 cm/s); the latter was also true for P. tomosvaryi although it favoured smaller sediment grain sizes (median = 32.4 mm). Species richness and population density increased from source to mouth. At sampling sites near the source Simuliidae were completely lacking. In headwaters only P. tomosvaryi was present, whereas the S. ornatum-group and Simulium (Simulium) argyreatum Meigen was collected exclusively near the mouth. 相似文献
9.
枝角类溞会由于捕食者的存在而发生形态、行为、生活史等的变化.通过为期10 d对太湖春、夏季优势种同形溞(Daphnia similis)在有幽蚊幼虫(CL)、无幽蚊幼虫(CK)及培养过幽蚊幼虫的过滤水(FL)3个环境水平的模拟实验,发现同形溞在有幽蚊幼虫和培养过幽蚊幼虫的过滤水处理下平均体长、累积产仔数及平均产仔数均显著大于无幽蚊幼虫组,表明幽蚊幼虫释放的信息素能改变同形溞的体长、产仔数等生活史参数,这种改变会降低同形溞被捕食的风险.说明在自然环境下,幽蚊幼虫等无脊椎捕食者能通过直接捕食和信息素的间接作用共同影响枝角类种群. 相似文献
10.
L. Snchez-Velasco M.F. Lavín M. Peguero-Icaza C.A. Len-Chvez F. Contreras-Catala S.G. Marinone I.V. Gutirrez-Palacios V.M. Godínez 《Continental Shelf Research》2009,29(14):1697-1710
The northern Gulf of California (NGC) is characterized by seasonal hydrography and circulation (cyclonic in summer and anticyclonic in winter), by intense tidal mixing in the midriff archipelago region (MAR), and by coastal upwelling on the eastern side from autumn to spring. We examined changes in larval fish assemblages (LFAs) in relation with hydrography and circulation during both phases of the seasonal circulation, as indicators of changes in the pelagic ecosystem. A canonical correspondence analysis defined LFAs (r>0.70), which were related with: (i) the coastal current on the mainland shelf, (ii) the central eddy and (iii) the MAR. In the early cyclonic phase, when the temperature and stratification were increasing and the coastal current was starting, demersal (Gobulus crescentalis, Lythrypnus dalli) and mesopelagic species (Benthosema panamense) dominated the NGC. The highest larval abundance was in the Current LFA area and the lowest in the MAR LFA area. In the mature cyclonic phase, the larval abundance increased in the NGC and species characteristic of eastern boundary current systems such as Opisthonema libertate and Engraulis mordax displaced the demersal species and became dominant, together with B. panamense in the Current LFA area; the latter species dominated in the Eddy LFA area. In the early anticyclonic phase, the direction of the coastal current reversed and the temperature and larval abundance decreased. E. mordax and B. panamense larvae continued dominating the NGC with higher abundance in the MAR than in the Current and Eddy LFA areas. In the mature anticyclonic phase, E. mordax larvae dominated in the Current and the Eddy LFA areas with the highest abundance in the former, while M. productus larvae (an eastern boundary current species) dominated in the Eddy LFA area. Results showed that in the NGC, the dramatically seasonal and predictable hydrographic and circulation features trigger the seasonal spawning of the dominant species. The biological richness of the coastal current area, in both circulation phases, suggested that this area has an important role in the pelagic ecosystem functionality of the NGC. 相似文献
11.
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13.
《Limnologica》2017
The diets of monkey goby, Neogobius fluviatilis, and racer goby, Babka gymnotrachelus, which are the most abundant gobiids in the Dniprodzerzhynsk Reservoir (Dnieper River, Ukraine), have been studied on a diel basis across three summer months at one sampling site of the reservoir littoral zone. In total, 37 prey items were identified in the monkey goby diet and 39 prey items were identified in the racer goby diet during the sampling period. The most important prey were chironomid larvae and pupae, copepods, cladocerans, mysids, and juvenile fish and their importance varied depending on goby size, diel period, and month. Both gobiids showed clear patterns in their diel feeding activities. Both species fed over a 24-h period, but the monkey goby fed more actively during the daytime, while the racer goby fed more at night. Peak chironomid larvae consumption by the monkey goby were from 10:00 to 14:00 and from 22:00 to 02:00,, while those by the racer goby were in the night-time from 18:00 to 6:00. The consumption of chironomid pupae peaked at dusk and night for both gobiids. Total diet overlap index between the two gobiids, during all months and diel periods combined was 78.6 and it varied between different length groups. The lowest diet overlap indices were observed between the smallest and largest length groups of the two species, while the highest overlap indices were observed between the same length classes of different species and between the neighbouring length groups of the same species. A negative relationship was observed between the difference in the mean lengths of two gobiid species and the diet overlap index. The monkey goby and racer goby can reduce their competition and be successive due to several factors: (i) different spawning periods allowing them to utilise food resources available for their juveniles at different periods; (ii) different habitat preferences resulting in (iii) somewhat different prey choices; (iv) different feeding activity periods. 相似文献
14.
In the present study, we used mitochondrial cytochrome oxidase subunit I (COI) and nuclear D2 region of 28S rDNA sequence
data to examine the taxonomic status of the water mite species Hygrobates nigromaculatus from two types of freshwater habitats: lentic (lakes) and lotic (streams). Previous hypotheses about (sub)species status
of populations inhabiting lakes and streams based on differences in morphometric data and life-cycle strategy (parasitic vs.
non-parasitic larvae) were strongly supported by molecular data. Levels of COI and D2 28S rDNA differentiation between lake
and stream populations were much higher (ca. 18 and 7.5%, respectively) than those typically observed for populations of a
single species. Both lake and stream populations showed similar high levels of gene diversity (Hd = 0.894 and 0.836, respectively).
However, nucleotide within-population polymorphism was more than twice as high in lake populations as that in stream populations
(π = 1.33 and 0.60%, respectively). We hypothesize that the ancestral lake-dwelling population originated from a stream form
with parasitic larvae (here: H. setosus nov. stat.). For the observed populations, H. nigromaculatus individuals could be separated from H. setosus by distinct morphometric characters. The loss of phoretic parasitic larvae greatly decreased dispersal ability of lake-dwelling
mites and consequently also the gene flow between lake populations. Thus, relatively more differentiated genetic structure
in lake populations probably results from a stronger isolation between particular lake habitats, but this hypothesis needs
further extensive studies. 相似文献
15.
A new C15 acetogenin, cyclic enyne (12E)‐cis‐maneonene‐E ( 1 ) and (12Z)‐trans‐maneonene‐B ( 2 ), together with different secondary metabolites including sesquiterpenoid 2,10‐dibromo‐3‐chloro‐α‐chamigrene ( 3 ) and fatty acid aldehydes ( 4–8 ) were isolated from the petroleum ether extract of a red alga, identified as Laurencia papillosa, collected from the Saudi Red Sea coast. The L. papillosa crude extract and its active ingredient acetogenin ( 1 ) have been evaluated for the ability to control two main economically important pests, the confused flour beetle larvae Tribolium confusum and Culex pipiens mosquito larvae. Compound 1 showed high potential as a natural insecticide against these two pests. In the case of T. confusum larvae, the LD50 values were 0.21 and 0.16% after 6 and 12 days of treatment with crude extract and acetogenin, respectively. On the other hand, the resulting LC50 values of mosquito larvae bioassay were 30.7, 36.9, and 41.8 ppm after 24 h treatment against 2nd, 3rd, and 4th larval instars, respectively. Also, an increase of the insecticidal effects against mosquito larvae was recorded after extending treatment time to 48 h. 相似文献
16.
Any contact of blackfly larvae and pupae to the substrate they colonise relies on the adhesion of the secretion which is produced in their large labial glands. This secretion anchors their filter-feeding position, any locomotive activity, and the pupal cocoon as well. The secretion works as a biological adhesive which adheres to nearly any substrate surface — even to wood or the integument of other aquatic animals. We began analysing the proteinaceaous compounds of the labial gland secretions of Simulium ornatum (complex) Meigen. According to the SDS-PAGE and amino acid analyses, blackfly gland secretion consists of a variety of proteins ranging from high to low molecular weights. The most prominent proteins form broad bands at about 70, 40 and 20 kDa. These main proteins were present in secretions from young to old larvae as well as in pupal cocoon secretion, but their relative amounts change with larval development. Results of N-terminal sequencing of prominent proteins revealed no obvious homologies to protein sequences deposited in the databases up to now. 相似文献
17.
Rh. germanica is a European species that, due to human impacts, has progressively disappeared from its original territories and is now considered rare. In SwitzerlandRh. germanica has disappeared from the Aare, Broye and Kleine Emme rivers and is actually found in a limited reach of the River Rhine and some of its tributaries (Limmat, Sihl, Thur and Töss rivers).Rh. germanica is a univoltine species, hatching probably in summer. The emergence occurs from February to the beginning of April. It takes place on the water surface. Laboratory observations have shown that the subimaginal stage lasts four days.Rh. germanica occurs on different substrate types, ranging from stones and cobbles to pebbles and gravel. The larvae are more abundant in zones of erosion with coarse and porous sediments than in depositional zones with fine sediments and silts. They are most abundant in riffles with water velocities from 20 to 150 cm/sec. The species tolerates moderately organic-polluted waters.The particular strategy concerning growth and emergence ofRh. germanica is also discussed. 相似文献
18.
探究鱼类繁殖策略是了解鱼类种群动态的关键.通过对珠江西江流域重要的经济鱼类广东鲂(Megalobrama terminalis)生殖周期、产卵时间、成熟期长度、生殖力类型和生殖力等方面进行研究,阐明在人类活动日益加强下,西江广东鲂的繁殖策略适应性变化情况.研究表明,广东鲂个体平均体长245 mm,优势体长集中在260~280 mm,平均体重347 g,优势体重集中在320~480 g.用L 50逻辑斯谛回归方法推算广东鲂雌鱼和雄鱼初次性成熟体长分别为244.5和232.2 mm.雌雄性比例为1.105∶1,且随着体长增加,雌雄性比呈现出先下降后上升的变化趋势.广东鲂繁殖群体在产卵季节为48月,产卵高峰为6月初持续到7月上旬,产卵季节内广东鲂鱼苗的密度与径流量显著相关.广东鲂绝对繁殖力平均为73069粒,相对繁殖力平均为118.7粒/g,绝对繁殖力与体长和体重均呈正相关.广东鲂繁殖群体性腺成熟系数与性腺重、肥满度以及体重密切相关.广东鲂种群繁殖策略在人类活动加剧影响下呈现出适应性变化:初次性成熟体长变小,绝对繁殖力下降. 相似文献
19.
The toxic effects of the water accommodated fraction (WAF) of a natural gas condensate on the larvae of five brooding coral species of the Family Pocilloporidae were examined in short term (96 h) bioassays. Lethality was observed in some larvae of Seriatopora hystrix and Seriatopora guttatus upon exposure to high concentrations of the condensate WAF, while those of Stylophora pistillata, Pocillopora damicornis and Pocillopora verrucosa did not experience mortality. Furthermore, increasing concentrations of WAF produced either delayed or impeded metamorphosis for all species except P. damicornis. Growth of juveniles, exposed to different WAF treatments for 96 h during their larval/early juvenile stages, was measured after 30 d. Marked decrease in subsequent growth rate (polyp count) was observed for S. hystrix, S. guttatus and S. pistillata with increasing WAF concentration. The results showed differential susceptibility of larvae of closely related coral species to oil stress, with the following sensitivity ranking: S. guttatus>S. hystrix>S. pistillata>P. verrucosa>P. damicornis. Oil exposure during the planktonic, larval stage of susceptible corals can adversely affect survivorship, recruitment and/or subsequent colony growth, thereby having profound consequences for the abundance of these corals in space and time. 相似文献
20.
From April 1997 to June 1998 Nemurella pictetii populations were regularly sampled in two springstreams at 220 and 850 m a.s.l., respectively, in Hesse (Germany), at approximately 51°N. Random samples of larvae were taken at three week intervals during the vegetation period, and once a month during winter. Sex, instar, body length, head capsule width and wing pad length of all larvae were recorded. Temperatures were recorded every hour, temporal patterns of temperature agreed closely between sites. Mean winter lows were 3.9 °C at both sites, the mean summer high was 11.9 °C at the lower site, as opposed to 9.6 °C at the mountain site.At both sites, adult emergence started in May. At the mountain site, recruitment started in late July and continued into autumn. There was cohort splitting in the young generation. Some individuals grew rapidly until October–November, but last instar larvae first appeared in March the next year. 1600 degree-days above 0 °C were accumulated during complete development. At the lower site, recruitment began in early July, and cohort splitting also occurred. Fast growing summer recruits emerged as adults in late August, having accumulated only 700 degree-days (above 0 °C). Their offspring hatched in November-December and emerged the next spring, having accumulated also only 700 degree-days. However, only part of the population was bivoltine. Many of the summer recruits grew more slowly and accumulated close to 1900 degree days until they emerged the next spring, together with the offspring of their own fast-growing siblings. Dependence of growth rate on temperature could not be estimated and appears to vary with daylength. For example, 3–6 °C support growth and development provided daylength exceeds 10 hrs of light, or is rising.At both sites and in all cohorts individuals emerging earliest were larger than later emerging ones. The size decline is significantly correlated with number of days after the winter solstice. For the first time it is shown that the decline does not occur shortly before adult emergence but actually takes place several instars before the last. Size differences are then carried on, and amplified, during subsequent molts, until adulthood. The literature presently relates seasonal size declines of insects to high or rising temperatures experienced by larvae approaching adulthood. Our data show that, at least in Nemurella, this explanation fails. On average, females were distinctly larger than males. Differences in mean last instar size were noticed also between sites and years. They remain presently unexplained. The mean sex ratio in both populations was close to 1:1. 相似文献