Diel activity of the pink shrimp Penaeus duorarum

Twelve juvenile pink shrimp, Penaeus duorarum Burkenroad, were tested individually for 3-day periods in electronic shuttleboxes to determine their diel patterns of locomotor activity, in relation to a natural summer photoperiod. Nocturnal activity was twice that exhibited during the daytime; however, a bimodal pattern was evident with crepuscular peaks occurring at dawn and dusk. The dusk peak was more pronounced, with activity increasing markedly before sunset (indicative of an endogenous circadian rhythm component), and continuing during the initial hours of darkness, gradually declining later during the night with a secondary peak at dawn falling off to minimal activity during daylight. Crepuscular activity (mean of dawn and dusk) was twice the nocturnal average.     

The response of Chironomidae (Diptera) to a long-term exclusion of terrestrial organic matter

We examined the effects of a seven-year detrital exclusion on chironomid assemblages in an Appalachian headwater stream. We hypothesized that litter exclusion would lead to a reduction in all chironomids at both the subfamily and generic levels because organic matter serves as both food and habitat in these headwater streams. Tanytarsini total abundance and biomass significantly declined after litter exclusion. Before litter exclusion, Tanytarsini average abundance was 4271 ± 1135 S.E. m⁻² and 625 ± 98 after litter exclusion. Biomass was 3.57 ± 0.96 mg AFDM m⁻² before litter exclusion and 1.03 ± 0.9 after exclusion. In contrast, Orthocladiinae abundance and biomass did not change because a psammanophilic chironomid, Lopescladius sp., and other Orthocladiinae genera did not decline significantly. Overall chironomid taxa richness and diversity did not change as a result of litter exclusion. However, Canonical Correspondence Analysis (CCA) of genus-level biomass did show a clear separation between the litter exclusion stream and a reference stream. Separation of taxa between the two streams was due to differences in fine (r ² = 0.39) and coarse (r ² = 0.36) organic matter standing stocks and the proportion of small inorganic substrates (r ² = 0.39) present within a sample. As organic matter declined in the litter exclusion stream, overall chironomid biomass declined and the chironomid community assemblage changed. Tanytarsini were replaced by Orthocladiinae in the litter exclusion stream because they were better able to live and feed on biofilm associated with inorganic substrates. Handling editor: K. Martens     

Diel emergence patterns of lotic Chironomidae

SUMMARY. Six channels were constructed in various parts of two riffles from which chironomid exuviae were collected every 3 h for three 24-h periods in July 1974. Diel emergence patterns were calculated for twelve abundant species and six different patterns were observed.
Krenosmittia cf. camptopheleps and Cordites had their major emergence pulse during peak light periods and it is proposed that high or increasing light intensity is a cue for their emergence. Stempellinella cf. brevis begins its emergence in the morning and continues until after darkness. Increasing and high water temperatures are suggested as the emergence cue since emergence tracks water temperatures with little apparent effect of light. Parametriocnemus sp. and Polypedilum ( Tripodura ) sp. begin emerging in late evening and continue into early daylight hours. These patterns indicate low and decreasing water temperatures as the emergence cue with little apparent effect of light. Corynoneura sp. and Thienemanniella sp. emerged primarily during daylight hours with a minor pulse in the morning and the major pulse in late afternoon. It is proposed that the emergence cue is simply the presence of light and that water temperature determines how many individuals are able to prepare for emergence and respond to the cue. Rheotanytarsus cf. exiguus and Tanytarsus ( Sublettea ) coffmani have major emergence peaks just after sunset and minor pulses in the morning hours. Changes in light are proposed as their emergence cue with water temperatures determining the number of individuals able to respond to that cue. Eukiefferiella discoforipes gr. sp. and Nilotanypus sp. emerge continuously throughout daylight and darkness hours, showing no obvious pattern.     

The diel activity pattern of mountain hare (Lepus timidus) on managed heather moorland in Scotland

The research presented in this paper provides an insight into the behavioral ecology of mountain hares on heather moorland in the Lammermuir Hills of southeast Scotland. We examine the seasonal and diel activity patterns using camera traps over a period of 12 months. The rate of camera detections was calculated for the different divisions of the 24‐hr cycle (daylight, dusk, night, and dawn). During autumn and winter (October–February), the activity pattern was crepuscular with greater activity at dusk than at dawn. Daylight activity was relatively low, and there was a regular pattern of small peaks of activity during the night. In spring and summer (March–September), peaks of crepuscular activity remained evident but daylight activity was much more prevalent than during autumn and winter, and night activity was lower. We discuss the problematic definition of twilight and present an explanation for seasonal changes in the pattern of diel activity that is linked to the reproductive cycle of the mountain hare.     

Diel emergence patterns of chironomids

The diel emergence patterns of 16 chironomid species from a Berkshire lake are characterized. A study of these patterns and those described previously in the literature indicate that the diel pattern for any chironomid species can often be predicted on the basis of the Tribe to which it belongs. Chironomini spp. usually emerge at dusk or at night. Macropelopiini spp. and Metrioenemini spp. characteristically emerge during daylight but the former peak in the morning and the latter peak in the afternoon. Orthocladiini and Tanytarsini spp. exhibit more varied patterns although bimodalism is a frequent feature. The phylogenetic conservatism in the diel patterns displayed implies that these patterns became established early during chironomid evolution, and are, therefore, plesiomorphic.     

Laboratory investigation on community composition, emergence patterns and biomass of wood-inhabiting Chironomidae (Diptera) from a sandy lowland stream in Central Europe (Germany)

Wood-inhabiting chironomid communities were investigated from June 1998 to July 1999 by laboratory rearing of randomly collected submerged branches from a headwater and mid-reach site of a sandy lowland stream, separated by an impoundment used for fishery purposes. Total annual emergence (males and females) from headwater samples was higher (2551 ind m^–2 y^–1) compared to the mid-reach (1576 ind m^–2 y^–1), which could be due to disturbances caused by frequent impoundment openings resulting in high discharge events. Chironomid community from branches comprised three subfamilies, with Orthocladiinae (18 species, 2189 ind m^–2 y^–1) clearly predominating at the headwater (total of 36 species). Mid-reach samples (total of 48 species) showed similar emergent numbers of Orthocladiinae (19 species, 786 ind m^–2 y^–1) and Chironominae (26 species, 764 ind m^–2 y^–1). Tanypodinae were caught very rarely in the laboratory emergence (12 ind m^–2 y^–1 at both sites). Shannon-Wiener diversity index for the mid-reach chironomid community was higher (2.52) than for the headwater community (1.68). Chironomid species composition on woody debris was similar between stream sites, with a Sørensen index of 0.75, but showed different dominance structures indicated by a Wainstein index of 0.26. Total adult biomass (in the manner of dry mass) during the study period was higher for wood-dwelling chironomids from the headwater (158.2 mg m^–2 y^–1) compared to the mid-reach (123.8 mg m^–2 y^–1), but individual biomass was higher for mid-reach chironomids (0.079 mg ind^–1 vs. 0.062 mg ind^–1 at the headwater), indicating the predominance of larger species. Total biomass of wood-inhabiting chironomids in the investigated lowland stream was low compared to other field emergence studies, which could be attributed to the laboratory approach for investigating the emergence from a single substrate type (submerged wood) instead of the integrative field surveys where chironomids from all habitats were caught. Main reason for the lack of chironomid species closely associated to wood in this sandy lowland stream could be infrequent but episodic disurbances caused by the anthropogenic induced highly fluctuating discharge regime of the downstream study site.     

Temporal and spatial distribution of chironomid larvae and oligochaetes in two Dutch storage reservoirs

Long-term changes in distribution and taxonomic composition of chironomid larvae and oligochaetes in two water storage reservoirs in The Netherlands were studied. A succession among the chironomid species was observed. In the last 10–15 years chironomid densities varied. Compared with other lakes chironomid densities were high. Densities of chironomids were higher in the littoral zone than in the profundal zone. The opposite was found for oligochaetes. Densities and composition of the chironomid fauna in the two reservoirs were similar.Procladius, Tanytarsus andHarnischia dominated at all depths. However, pupal exuviae samples showed some differences in chironomid taxonomic composition between the two reservoirs. Orthocladiinae, rarely found in bottom samples, abounded in pupal exuviae samples.     

The dawn flight of the gold swift Hepialus hecta: predator avoidance and the integration of complex lek behaviour (Lepidoptera,Hepialidae)

Predator pressure is a considerable evolutionary force. The evening twilight flight of species in the family Hepialidae Swift moths has been attributed to the moths (which have no hearing and so cannot detect bats) flying in a bat/bird free window. Several species deploy elaborate lek behaviour in this period. The expected flight in the dawn twilight is little reported, except in the non‐leking Hepialus (Korscheltellus) gracilis. A detailed study of the dawn flight in the leking species Hepialus (Phymatopus) hecta shows that it is less extensive than the evening lek flight (both in duration and in the number of moths participating), is confined to a much narrower window around sunrise, involves no reproductive behaviour, and functions only to re‐locate the members of copulating pairs and sessile displaying males from the emergent ground vegetation to less conspicuous roosting sites. Compilation of individual biographies over the 24‐h cycle permits a full construction of the diel activity in time and space. It consists of two twilight flight periods, separated by prolonged roosting during the hours of darkness and daylight. The moths use almost the whole available range of roosting sites, from the base of the ground vegetation to the tree canopy, and cyclically leave and re‐enter the lek site from these positions. The copulating posture and position avoid mammalian predators, and facilitate escape from spiders and wasps by the efficient use of a dead drop. The narrowness of the dawn flight is attributed to the need for this prolonged but conspicuous copulation, which precludes a morning mating, and to a demonstrated asymmetry of twilight activity in birds. The whole integrated spatio‐temporal cycle is attributable to evolutionary pressure to minimize the impact of predators, demonstrated to include birds, bats, wasps, and spiders, and probably also dragonflies, mice and shrews; the pre‐existing dawn flight is permissive to the evolution of sessile male displays during the evening lek. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 305–319.     

Population dynamics of Tenagomysis tasmaniae Fenton,Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea:Mysidacea)

The population dynamics of a coastal mysid community was examined at One Tree Point in southern Tasmania over a 12-month period, including three 24-hour sampling sessions. Fourteen mysid species were recorded. Zonation patterns, life-history and diel activity of the three most abundant species, Tenagomysis tasmaniae, Anisomysis mixta australis and Paramesopodopsis rufa were examined. These three species were found in large numbers throughout the year associated with the macroalgal fringe on either side of the bay. Habitat partitioning within this zone of occurrence was evident. T. tasmaniae was the most abundant species (annual mean density 32.4 m^–3), followed by A. mixta australis (annual mean density 20.5 m^–3 ) and P. rufa (annual mean density 11.3 m^–3). The major peaks of abundance of these three species were temporally separate. Breeding was intensive for the three species from spring till late autumn. A cessation of breeding in winter was evident for A. mixta australis and to a lesser extent for P. rufa but T. tasmaniae bred throughout the year although at a reduced rate during winter. Examination of the diel behaviour identified peaks of abundance at sunrise and sunset for T. tasmaniae; P. rufa was caught in greater numbers at night, but no consistent pattern was observed for A. mixta australis.     

Diel variation in chironomid (Diptera: Insecta) exuviae abundance and taxonomic richness in near-pristine upland streams of the Greater Blue Mountains World Heritage Area,South-Eastern Australia

We assessed diurnal variation of Chironomidae exuviae in two small upland streams in temperate Australia, during summer. Understanding the diel periodicity of exuviae can be an important consideration for biomonitoring purposes or to investigate adult emergence patterns. We collected 1,813 floating exuviae, comprising 54 taxa from four subfamilies, from flowing water using a drift net. Unlike many northern hemisphere temperate studies, we observed that peak exuviae abundance (7.3 exuviae per m3) and taxon richness (1.7 taxa per m3) occurred in the dusk and night hours, with the lowest numbers (0.9 exuviae per m3) and taxon richness (0.6 taxa per m3) recorded in the late morning to early afternoon. We suggest that this could be an adaptation to avoid stressful weather during the heat of summer days, or it could be to avoid visual predators. The numerically dominant taxa exhibited peak abundance in the dusk/night samples which indicates predominant crepuscular/nocturnal patterns of adult emergence. This pattern was consistent across both streams surveyed. Our taxon inventory rose steeply during the first 24-h occasion, then at a reduced rate during the second and third days of sampling. For flowing water collections of exuviae that utilise drift-netting, we suggest that sampling at all sites includes at least three 24-h cycles and avoids periods of heavy rainfall and increased stream flow.     

A note on chironomids (diptera) of temporary pools in the National Park of Circeo,Central Italy

Preliminary observations on chironomid assemblages in 9 temporary pools of the National Park of Circeo (Central Italy) are reported. A total of 15 genera or species groups (6 Orthocladiinae, 3 Tanypodinae, 1 Tanytarsini and 5 Chironomini) were recorded during March and April, 1986.Psectrotanypus varius, Polypedilum nubeculosum gr.,Chironomus thummi gr. andC. plumosus gr. were the most abundant and frequent taxa in the nine pools. Almost all chironomids collected are eurytopic and widely distributed in Europe, including Italian waters. Only the finding ofGymnometriocnemus is reported in this paper as a new record for Central Italy. Similarity among pools and among taxa (coefficient of Jaccard) shows a major occurrence of aquatic Orthocladiinae in smaller pools and of Chironomini in larger pools. This relationship between chironomid assemblages and pool sizes can be partly related to the duration of the wet phase which affects chironomid species according to their survival strategies.     

Activity patterns of Pipistrelle bats (Pipistrellus pipistrellus) in north-east Scotland

Pipistrellus pipistrellus emerge from their nursery roosts in north-east Scotland about 35 minutes after sunset, at light intensities of between 15 and 35 lux. Cloud cover, windspeed, ambient temperature, rain, light mist and moonlight have no apparent effect on the time or pattern of emergence. Throughout pregnancy and lactation, emergence lasts for about an hour. After weaning, when the adult females have left the roost, their young take about 40 minutes to emerge. The average rate of initial emergence is proportional to colony size, and the maximum rate of emergence occurs half way through the exodus.
During pregnancy in May and June most bats leave the roost once each night soon after dusk and return between midnight and dawn. After parturition in late June the activity pattern becomes bimodal and the numbers of bats outside the roost show peaks after dusk and immediately before dawn. There is intermittent activity in the vicinity of the roost all night and bats make two or three flights each night. After weaning in August the activity pattern gradually ceases to be bimodal, and the number of flights per bat falls to between one and two. The average time spent outside the roost varies between 2–5 and 5 hours during the summer. The recorded activity patterns of night-flying insects are all bimodal, with peaks after dusk and before dawn, corresponding with the maximum number of bats outside the roost during lactation.     

Drift dynamics of Chironomidae larvae: I. Preliminary results and discussion of importance of mesh size and level of taxonomic identification in resolving Chironomidae diel drift patterns

Diel drift samples utilizing nets with mesh size less than 200 microns were taken in Linesville Creek, Pennsylvania, an eastern deciduous forest stream, and Inlet Run, Wyoming, an alpine snow melt stream. Identification of drifting Chironomidae larvae to lowest level taxonomic categories indicated 51 species or species group categories representing 51.95% of the total insect drift in Linesville Creek and 18 species or species group categories representing 70.47% of the total insect drift in Inlet Run. Orthocladiinae were the predominant larvae in the drift in Linesville Creek, with 19 species comprising 43.84% of the Chironomidae drift. In decreasing abundance were Chironomini (12 species, 40.36% of Chironomidae drift), Tanytarsini (10 species, 8.89%), and Tanypodinae (10 species, 6.91%). By contrast, Diamesinae were the predominant larvae in the drift in Inlet Run, (5 species, 71.43%) followed by Orthocladiinae (10 species, 27.25%), Tanytarsini (2 species, 1.20%), and Podonominae (1 species, 0.12%). Comparison of drift composition with substrate samples and/ or emergence data indicated a close relationship between relative abundance in drift and relative abundance in the benthos. Behavioral drift patterns with nocturnal peaks were seen for 3 species or species groups in Linesville Creek. Four species with diurnal drift peaks were present in Inlet Run. Analysis of the size distribution of drifting larvae indicates that a mesh size as small as 200 microns is required to resolve diel drift patterns. It is postulated that random factors greatly influence the apparent diel drift pattern of Chironomidae when nets with mesh size in excess of 400 microns are employed in drift studies. Conflicting literature reports of behavioral drift for Chironomidae may be due to differing species composition of drifting larvae and net mesh size related artifacts.     

The thermoregulatory function of diel vertical migration for a juvenile fish,Cottus extensus

Juvenile sculpin (Cottus extensus) less than 30 mm long exhibit a diel vertical migration in the limnetic zone of Bear Lake (Utah-Idaho). Using mid-water and bottom trawls we found that these fish inhabit the bottom of the lake (5° C) during the day but migrate 30–40 m into the water column at night where they reside in the metalimnion or epilimnion at temperatures near 13–16°C. Larger fish do not migrate into the water column. Stomach analyses demonstrated that the young-of-the-year fish do not migrate into the water column to feed: from July to October their diet is 70–93% benthic ostracods and copepods, and pelagic prey are rarely consumed. Furthermore, gut fullness of the sculpin increases through the daylight period and decreases through the night, reaching minimum levels just before the dawn descent. Laboratory experiments demonstrated that the diel migration would increase digestion rate from 3%/h at profundal temperatures, to 22%/h in the warmer surface water, thus allowing the fish to empty their guts overnight and permit feeding the following day. Additionally, sculpin held in a temperature and feeding regime that mimicked that experienced by migrating fish grew 300% faster than those reared at 5° C. Given the overwhelming importance of fast growth for juvenile fishes, a post-feeding thermotaxs that increases digestion may be a common phenomenon increasing growth, and affecting the distribution and bioenergetic relationships of fish.     

Species composition,abundance and emergence phenology of midges (Deiptera: Chironomidae) in a brown-water stream of West-Central Alberta,Canada

Sixteen floating, box type emergence traps, each covering 0.1 m², were placed along 150 m of a third-order stretch of the Bigoray River, a slow-flowing, vegetation-choked, brown-water muskeg stream. Effects of trap design, trap shading, length of sampling interval, and stream velocity on the number of midges caught was examined. Of the 112 species of Chironomidae caught, 32 species made up 90% of the catch and their emergence phenology is described in detail. There were more rare species than expected from Preston's lognormal distribution. Percentage of Bigoray species belonging to Tanypodinae, Orthocladiinae, Chironomini and Tanytarsini was 18%, 43%, 20%, and 19%, and was compared with 27 other studies on lotic chironomids. During the 140-day emergence period an average of 19.3 × 10³ chironomids emerged per square meter of stream. Based on changes in male:female ratios throughout a species emergence period, it was postulated that 30% of the Bigoray chironomid species were univoltine, 50% were bivoltine, and 20% were trivoltine.     

Seasonal dynamics of Chironomidae (Diptera) on the Bulrush Schoenoplectus lacustris in a chalk stream

SUMMARY. The chironomid fauna of a chalk stream in southern England is described from 1 year's catches of emerging adults and 2 year's quantitative samples of larvae on Common Clubrush, Schoertoplectus lacustris. The number of species in eaeh higher taxon as adult males and larvae on Schoenoplectus were: Tanypodinae, nine and three; Diamesinae, two for both; Orthoeladiinae, 26 for both; Chironomini. twelve and six; Tanytarsini, seven and five, respectively. A total of 66 species was recorded for both life stages. Adult Orthocladiinae were caught throughout the year. Tanytarsini were absent for a few weeks in winter, and Tanypodinae and Chironomini were caught for shorter periods in warmer months. Chironomids 93.5% of the total invertebrates on Schoenoplectus. Life histories are deseribed for seven speeies that formed 91% of the identified chironomids (32% of the total were unidentifiable first and second instar larvae). Four of these life histories appear for the first time. All seven species were multivoltine and had continuous recruitment for part of the year. The species diversity of larvae was mostly in the range 1.5–3.0 and it was determined more by equitability than by species richness. The numbers of chironomids through time were dependent on the weight of detritus on the leaves (r²= 0.69) and the availability of detritus therefore partly controlled their population size.     

Emergence of Chironomidae (Diptera) from a delta-swamp receiving thermal effluent

Chironomid pupal exuviae were collected over an eight-week period from a delta-swamp which receives thermal effluent from a nuclear reactor on the Savannah River Plant, South Carolina, USA. Two sites were sampled using box-type emergence traps. Site 1 was directly in a major thermal plume channel, and site 2 was outside the plume in a stand of stressed bald cypress trees. Sixteen chironomid taxa were collected, of these, species of Chironomus (42%) and Tanytarsus (35%) dominated the warmer site (site 1, maximum temperature 46 °C), whereas Tanypus neopunctipennis comprised > 84 % at site 2 (maximum temperature 43 °C). Emergence substantially increased at both sites after the reactor was shut down and water temperatures returned to ambient (27–28 °C). Tanytarsus sp. 1 and T. neopunctipennis were capable of successfully emerging during water temperature periods of 40–46 °C. The deep organic sediment, characteristic of the delta-swamp apparently served as a refugium for these and other species of midges during high temperature periods. It is suggested that the ability of some taxa to tolerate these elevated temperatures may be a combination of several factors: behavioral and ecological adaptations to utilize available refugia; and physiological adaptations to withstand higher temperatures and low dissolved oxygen concentrations.     

A preliminary survey of the Chironomidae (Diptera) of Costa Rica,with emphasis on the lotic fauna

Extensive collections of Chironomidae were made in Costa Rica, Central America, during 1986 and 1987. Fifty-five genera and at least 148 species belonging to the subfamilies Podonominae, Tanypodinae, Orthocladiinae and Chironomidae were found. Chironominae and Orthocladiinae predominated. Only one species of Podonominae was collected. Tanypodinae was represented by many genera, but species richness was low.Cricotopus was the most widespread and diverse genus of Orthocladiinae. Among the Chironominae the generaPolypedilum, Pseudochironomus, Tanytarsus andRheotanytarsus showed high species richness. Several species were collected that could not be assigned to genus. A number of range extensions were recorded for taxa found in the Neotropical region for the first time and for Neotropical taxa recorded outside of South America for the first time. The Costa Rican chironomid fauna consists of cosmopolitan, holarctic and neotropical components. There is probably an endemic Central American chironomid fauna at the species level.     

Zur Tagesperiodik des Schlüpfens von Ephemeropteren und Plecopteren

Zusammenfassung Am Ufer des Mondsees, Oberösterreich, wurde die Tagesperiodik des Schlüpfens folgender Insektenarten in einem Schlüpfkasten experimentell untersucht: Nemoura cinerea: Schlüpft während des ganzen Tages mit Maxima zwischen 6.00 und 10.00 Uhr und nachmittags; Ephemerella ignita: Schlüpfmaximum von 18.00–20.00 Uhr; Leptophlebia marginata, Ephemera danica und Centroptilum luteolum: Schlüpfmaxima von 12.00–16.00 Uhr.Die Dauer des Subimaginallebens der untersuchten Ephemeropterenarten wurde durch Aufzucht zur Imago festgestellt. Die Bedeutung dieser temperaturabhängigen Entwicklungszeit für die Tagesperiodik der Imaginalhäutung wird diskutiert.

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Summary The diurnal periodicity of emergence of several stonefly and mayfly species was studied on the shore of lake Mondsee, Austria. Nemoura cinerea (Plecoptera) emerges during the whole day with peaks in the morning and afternoon. The Ephemeroptera Leptophlebia marginata, Ephemera danica and Centroptilum luteolum emerge as subimagines at noon and in the afternoon, Ephemerella ignita in the evening around sunset. The duration of the subimaginal life of these mayfly species was determined. The importance of the temperature-dependent length of subimaginal life for the diurnal periodicity of the imagoes' emergence from subimaginal stage is discussed.

     

Emergence patterns of riverine dragonflies (Odonata: Gomphidae) in Hungary: variations between habitats and years

In this paper the results of a six-year study on riverine dragonflies (Odonata: Gomphidae) emergence based on the systematic collection of exuviae are presented. The exuviae were counted to determine variations in species composition, abundance and emergence pattern of gomphids at four different sites along the rivers Tisza and Szamos, as well as at a selected site in five different years. While the number of species decreased, the abundance of exuviae increased downstream the river Tisza. The total numbers of exuviae differed significantly between the dammed and non-dammed sites. The emergence of gomphids varied in initiation, synchronisation and also in duration between sites as well as between years. The onset of emergence was dependent mainly on the species-specific temperature sums, consequently earlier or later emergence resulted from the differences in the spring water temperature. The duration of emergence in G. flavipes and G. vulgatissimus was twice as long at the dammed site, characterised by a higher larval density, as at the other sites. In the degree of synchrony G. flavipes showed the emergence characteristics both of the spring and the summer species. Such interyear variations at the same site might have been attributed to the differences in annual fluctuations in the water temperature, indicating that rising temperatures may influence not only the onset of emergence but the synchrony as well.