Random patch dynamics of larval Chironomidae (Diptera) in the bed sediments of a gravel stream

• 1 The larval chironomid community of the sediment surface and the hyporheic inters titial was investigated in two longitudinal transects of an alpine gravel stream between September 1984 and August 1985. Eighty larval species and species groups were identified, most of which belonged to the subfamily Orthocladiinae. Of all larval individuals 51.1% inhabited the first 10cm of the bed sediments, and 93.2% occurred between the surface and 40cm depth.
• 2 The spatial species turnover showed marked variations between horizontally adjacent sampling sites in each of the four sediment depth layers. In both transects the species composition showed a significantly lower turnover in the upper 10cm of the bed sediments than in the deeper layers.
• 3 Spatial community stability showed an oscillating pattern between all sampling sites due to density shifts of larvae between depth layers. Temporal differences in resilience (local stability) were significantly and positively related to changes in the cumulative discharge pattern in the gravel brook, thus indicating the apparent ability of the community to recover quickly following disturbances.
• 4 The five abundant species, Corynoneura lobata, Synorthocladius semivirens, Tvetenia calvescens, Micropsectra atrofasciata and Rheotanytarsus nigricauda, exhibited significant differences in their sediment depth distribution, with density maxima shifting between depth layers. Spatial autocorrelations suggest that these larvae form patches between neighbouring sampling sites with varying sizes and inter-patch distances in each of four sediment layers. A simulation test, in which individuals of each species were randomly permuted between microhabitats of each depth layer separately, indicated that the patches might have arisen by chance.
• 5 To evaluate the significance of observed spatial resource overlap values amongst these five chironomid species, neutral models were developed based on 300 randomizations of each possible species pair-wise association of individuals and patches of species. The spatial organization of a larval chironomid assemblage in the stream Oberer Seebach seemed to be governed by coexistence due to random patch formation and dispersal patterns within the interstitial habitats, which reduce the probability of strong competitive interactions.

     

Biology of epiphytic Chironomidae (Diptera:Nematocera) in chalk streams

Submerged macrophytes are a conspicuous feature of chalk stream ecosystems, supporting large populations of diatoms and invertebrates, including larvae of the nematocerous family Chironomidae. Close temporal and spatial association is evident between chironomid larvae and diatoms, and diatoms are frequently a major component of the food of midge larvae. Larvae provided with food that is rich in diatoms survive better and grow and develop more quickly than larvae that are supplied with food that is predominantly fine organic detritus. First instar larvae selectively feed on diatoms but it is likely that selection is on the basis of particle size, rather than for diatoms per se. Three species of epiphytic larvae (2 Cricotopus spp. and Eukiefferiella ilkleyensis) transfer to a diet that is predominantly of fresh plant material (Ranunculus calcareus leaves) in the third and fourth instar. The life cycle strategies of many species of Orthocladiinae equip them to exploit temporarily favourable environmental conditions very rapidly and effectively. This fact helps to explain the coexistence of species with similar strategies of resource utilization, as part of the normal epiphytic fauna of chalk streams.     

Ecological synopsis for Chironomus flaviplumus (Diptera: Chironomidae) in the Jung-rang stream

In this study, we conducted field sampling to assess the relative influences of water and substrate quality on benthic macroinvertebrate communities living in the Jung‐rang stream, Korea. We collected macroinvertebrates and assessed physicochemical variables from three sites in the stream between May 2001 and January 2002. Sites were located approximately within 20 km from the headwater. The structure of the benthic macroinvertebrate communities may be strongly affected by the physical conditions inherent to the environment in which they live. In this stream, we detected profound differences in water temperature (18 ～ 19.75°C), the concentrations of suspended solids (3.935 ～ 7.87 mg/L), and demand for chemical oxygen (10.575 ～ 14.425 mg/L). Nonylphenol concentrations ranging from 0.375 to 0.55 ng/mL were found in the water, and the sediments were measured to contain between 2.45 and 3.425 ng/mL. We identified a total of 20 macroinvertebrate species, including seven species of Chironomidae, the most abundant of which was Chironomus flaviplumus. At none of the sites did we find any significant differences in the structure of the communities. Using canonical correspondence analysis for the relation of species and environmental variables, chemical oxygen demand and suspended sediment gradients (SS) had significant preferences for site 1 with SS. The results of our study suggest that physico‐chemical variables exerted complex effects on the structure of the benthic community in the Jung‐rang stream. This study supports the contention that physico‐chemical analyses as well as community analysis are valuable tools to assess the effect of pollution on the ecological condition of a stream. Chironomids, in particular, showed a high degree of tolerance against contaminants.     

Densities ofProdiamesa olivacea (Neigen) (Diptera: Chironomidae) in a second order stream,the Laan (Belgium): Relation to river dynamics

Larval densities ofProdiamesa olivacea were examined in the Laan stream for one year and matched against stream discharge and coarse organic detritus (COD) content of the sediments. The sediment grain size partitioning for the 12 monthly sampling dates was also assessed. The substrate was mainly composed of fine sand (high discharge periods) or silt (low discharge periods) and a never absent COD component which fluctuated seasonally within a narrow range. The discharge fluctuations showed some negative impact on densities of early instarP. olivacea. The absolute and relative densities ofP. olivacea were high throughout most of the study period and showed emergence periods in April–May and September–October.     

Seasonal influence on head capsule deformities in Chironomus zealandicus (Hudson) (Diptera: Chironomidae)

The natural incidence of deformities in the head capsules of Chironomus zealandicus was investigated at four lake sites in the central North Island (New Zealand) in summer (December) of 1994, 1995 and 1996, and winter (June) of 1995 and 1996. Significant differences were observed in deformities between sites and seasons. Individuals from Hamurana Stream, a relatively clean site, had the lowest incidence of deformities. However, there were still significant numbers of deformed chironomids. The incidence of deformity increased in summer in larvae from all sites except Hamurana Stream. No seasonal differences were observed in larvae from Hamurana Stream. There are indications that substrate type, season and genetic factors, as well as sediment chemistry may have collectively contributed to the incidence of head capsule abnormalities in C. zealandicus.     

Spatial distribution and diversity of chironomid assemblages in a small hilly stream (Diptera: Chironomidae)

In 2006–2007, spatial variations of chironomid assemblages of a small chalky watercourse were investigated in the hilly region of Balaton Upland, Hungary. Samplings were carried out every three weeks at seven characteristically different sites along the whole length of the watercourse. Altogether 2966 specimens were collected and identified. The chironomid fauna of the stream was relatively rich with 40 taxa belonging to four subfamilies (eight Tanypodinae, one Prodiamesinae, 17 Orthocladiinae, 14 Chironominae). The lowest number of species and number of individuals was found at the spring, and the highest at the middle reach. Based on multivariate analysis the different sections of the creek were characterised by distinctive chironomid communities. Although longitudinal changes in the chironomid community of the Örvényesi creek were detectable due to changes in natural environmental factors, land-use changes also significantly influenced the chironomid community composition and diversity. The natural and anthropogenic effects were hardly distinguishable. Furthermore, we found that the response of different diversity indices to environmental variability was different. This draws attention to the difficulties in evaluating the relationships between stream communities and environmental variables using different diversity indices. The taxonomic diversity, which incorporates the taxonomical relationships between the specimens, proved to be one of the most useful diversity indices to characterise the stream chironomid assemblages.     

Water quality and the occurrence of Chironomus riparius Meigen (Diptera: Chironomidae) in a stream receiving sewage effluent

SUMMARY. The effects of a sewage effluent in Moat Brook, Staffordshire, were determined from regular collections of water and biological samples from directly comparable stations above and below the sewage outfall.
The eutrophic conditions below the outfall result in the replacement of Polypedilum laetum by Chironomus riparius (except in the spring) as the dominant member of the Chironominae. Continuous recruitment of first instar larvae to the population of C. riparius in summer and autumn results in much overlap of generations, but emergence trap captures suggest at least five generations in the year.
The usefulness of C. riparius as an indicator of enriched conditions in lotic ecosystems should be considered in relation to oviposition behaviour and the occurrence and seasonal variation in density of the adults and aquatic stages (including the more conspicuous third and fourth instar larvae).     

Seasonal dynamics of a mayfly (Insecta: Ephemeroptera) community in a Laurentian stream

The purpose of our study was to compare on a seasonal basis the emergence, the drift and the benthos on a short and uniform section (18.5 m)of a stream in the Laurentian Hills of Québec. Nineteen species occurred on this stretch, but only six were abundant: Leptophlebia cupida (Say), Habrophlebia vibrans Needham, Baetis pygmaeus (Hagen), Eurylophella verisimilis (McDunnough), Stenonema modestum (Banks), and Stenonema vicarium (Walker). Emergence was monitored for 5 years; densities differed from one trap to the next, as did species dominance, but total densities were similar. These data conform to Illies' rules of constancy and harmony. Nymphal densities were high (mean of 16000 m⁻²). The dominant species were univoltine, except H. vibrans (semivoltine), and B. pygmaeus (polyvoltine). Larger species contributed relatively more to the production of the reach despite their low densities than did the more abundant smaller species, especially those with long life cycles. Drift was low during most of the year, except during spring and species composition varied considerably. A comparison of the three data sets (emergence, drift and benthos) shows a general agreement for the less abundant species, but for three of the dominants, H. vibrans, L. cupida and E. verisimilis , movements of individuals to and from the reach at various times in the life cycle (adult flight, nymphal drift and migration) must be taken into account in order to correlate the data. None of the methods alone gives a satisfactory picture of the community structure, each is to some extent misleading and needs to be used in conjunction with the others; the conflicting results obtained from the data sets often reveal interesting life history traits which otherwise would not have been detected.     

Seasonal variability of the karyotype structure of Chironomus plumosus (Diptera, Chironomidae) from a biotope of Kaliningrad

Chironomus plumosus larvae from the polluted Shkolnoe lake, Kaliningrad, have 2n = 8 and 2n = 8 + B. In winter season we found 11 types of hetero- and homozygous inversions in A, B, C, D, E, and F arms whereas in summer season we registered 7 types of the same inversions in A, B, C, D, and E arms. All inversions with exception of the inversion in arm C correspond to Hardy-Weinberg equilibrium. The arm IVG shows homozygous increase of centromeric heterochromatin more frequently in summer than in winter (34.4% as compared with 1.8%). The arm E has asynapsis 2 times less frequently in summer than in winter (21.4% as compared with 44.6%).     

Notes on the Chironomid (Diptera, Chironomidae) Ocelli

Clear spots present on the imaginal head of many Chironomidae have previously been interpreted as vestigial ocelli. Scanning electron microscopy of clear spots in Diamesa tonsa (Haliday) and Protanypus caudatus Edwards indicates, however, that these structures are proprioceptive sensilla.     

Studies on Ephemerella ignita (Poda) in a chalk stream in Southern England

The nymphs ofEphemerella ignita occurred in all months except October in the Bere Stream at Bere Heath, a small chalk stream in Southern England. Peak densities of 1,498 m^–2 and 753 m^–2 were recorded in May by two sampling methods used simultaneously. The seasonal patterns of growth and abundance are compared with the findings of other authors. A maximum biomass of 0.82 g m^–2 preserved dry weight is compared with figures for two of the most common invertebrate groups present; the Simuliidae and Oligochaeta.     

Seasonal variations in the benthos of a chalk trout stream,the River Samson,Belgium

Seasonal variations in the benthos of a Belgian chalk stream were investigated. Total biomass varies extensively over the year (30 to 100 g wet wt. m^–2). In summer, however, it is smaller than fish biomass. Densities range from 30 000 to 50 000 individuals m^–2, but the actual number of taxa is always near 60. Diversity indices (Shannon-Weaver and Pielou) exhibit slight fluctuations. Numerical indices are minimal in winter when the stream is in flood. Gravimetric indices are minimal in spring when biomass is maximal. Species-abundance curves almost always indicate a fauna with many rare species, with, also, some indication of a second maximum of moderately abundant species. Six taxa dominate: Oligochaeta, Gammarus fossarum, Ephemeroptera, Coleoptera, Trichoptera and Diptera. There are great fluctuations in their relative importance over a year. Thus, there seems to be a succession of peaks in densities of individual taxa permitting more efficient utilization of resources. However, biomass variations depend on the species involved. As a general rule, maximum biomass precedes maximum density.     

Seasonal population dynamics in Lucilia eximia (Wiedemann) (Diptera: Calliphoridae)

In this study the seasonal variation of fecundity, wing and tibia sizes were investigated in natural populations of Lucilia eximia (Wiedemann) as an attempt to determine the variations in life history of the species associated to seasonality. Specimens of L. eximia were monthly collected in Botucatu, S?o Paulo, Brazil, during two years and the adult females dissected to estimate fecundity. Body size was estimated by measuring wing and tibia. Fecundity and body size were seasonally analysed. A relatively constant temporal trajectory was found for fecundity, wing and tibia size over twenty-four months. Strong positive correlations between wing and tibia size, fecundity and wing and fecundity and tibia were observed. The maintenance of stable values in L. eximia indicates that it has suffered little seasonal influence over the period analysed. This result confirms the demographics and life history stable profile of the species in spite of seasonal climatic changes observed in the study area.     

Population dynamics and resource utilization by larval Chironomidae (Diptera) in a backwater area of the River Danube

1. The five most abundant species of the larval chironomid community in a backwater area of the River Danube were analysed in terms of population dynamics and utilization of space from July 1985 to July 1986. The life histories of Prodiamcsa olivacea (Meigen), Cryptochironomus defectus (Kieffer), Harnischia curtilamellata (Malloch), Polypedilum laetum (Meigen) and Polypedilum scalaenum Schrank were described; the number of estimated generations per year was two for P. olivacea, H. curtilamellata, P. laetum and P. scalaenum and three for C. defectus. A decline in larval densities of P. olivacea and P. scalaenum was significantly correlated with increasing cumulative water discharge in an area close to a dam (P<0.01). 2. Spatial overlap and resource width were estimated for these chironomid species across four ranges of water depth, in three sections of the River Danube. An increasing mean spatial overlap between larval species coincided significantly with higher mean resource utilization in all cross-sections during the sampling period. Simulations of spatial overlap between randomized species associations were conducted for analyses of coexistence and dispersion between larval populations. On the basis of comparison with a neutral model, in which patches of individuals were randomly reassigned to habitat units, spatial segregation was significantly (P<0.05) different from chance for seventy-three out of 263 species pairs examined through the year. 3. An analysis of the spatial dispersion of each chironomid species (using the standardized Morisita index) suggested temporally and spatially varying patterns of dispersion, whereas the mean spatial segregation between patches of larval species might have resulted from temporary formations of random patches in this backwater area of the River Danube. 4. Spatial stability estimated as the minimum positive eigenvalue of the species matrix was significantly positively related to mean spatial segregation, indicating that a lower habitat segregation between patches of larval species pairs may lead to a destabilization of the larval species assemblage.     

Seasonal Dynamics of a Chironomus plumosus (L.) (Diptera,Chironomidae) Population from a Fish Pond in Southern Bohemia

A population of Chironomus plumosus (L.) from a fish pond has been investigated for two years. Quantitative benthic samples and emergence traps were used to study the seasonal dynamics. Effect of some factors on the duration of development was studied in laboratory experiments. Data on larval abundance, length frequency analysis and emergence of adults suggest a bivoltine life cycle. The population of C. plumosus investigated showed a pronounced tendency to dormancy, even under long-day conditions. Factors regulating the bivoltine life cycle are discussed.     

Temperature-dependent growth rates of larval midges (Diptera: Chironomidae) from a southeastern U.S. stream

Inland aquatic ecosystems and their biodiversity in Asia represent a wide spectrum along a complex continuum of interacting ecological, economic, socio-cultural and political gradients all of which determine their present and future. Whereas the diversity of biophysical environments ensures a rich inland aquatic biodiversity, their present status has been greatly influenced by human societies that have depended on them for millennia. Besides high population densities and developmental pressures, socio-cultural factors, economic considerations and various policies concerning land and water resources are major factors responsible for the degradation of habitats and loss of biodiversity. The looming global climate change may only worsen the situation unless remedial measures are taken on a large scale and urgently. The future of aquatic biodiversity in Asian countries will depend upon a radical change in national policies on water, and upon research that can support the development of appropriate policies.     

Life cycle ofPseudodiamesa branickii (Chironomidae) in a small upland stream

The generation time ofP. branickii was studied using larval samples in conjunction with rearing experiments and continuous collection of egg masses across one year. This species produced three generations per year in a central German stream (280 m a.s.l., 50° 40 N). Its generation time was variable and obviously influenced by the photoperiod to which eggs and larvulae were subjected. It is thus concluded that two strains ofP. branickii were present in a single population, one bivoltine and the other trivoltine.     

A review of the genusChironomus (Diptera,Chironomidae)

Two cytologically distinguishable species have been found in material ofChironomus australis. These species have been calledCh. australis andCh. duplex. Both belong to thepseudothummi-cytological grouping because they have the chromosome arm combinations AE, BF, CD, G.Ch. duplex shows a modified arm pattern due to a tandem fusion of arm G to arm E.—The banding patterns of the polytene chromosomes of the two species are compared to each other and to the Australian standard species,Ch. oppositus. Ch. australis is very close cytologically toCh. oppositus, whileCh. duplex, which is considered a derived species because of the tandem fusion, shows a number of inversion differences from the morphologically similarCh. australis. Ch. duplex is polymorphic for six inversions, four of which are simple inversions, the other two are complex involving also the transposition of some bands.Ch. australis appears to be monomorphic.     

Larval Chironomidae (Diptera) of the Big Thicket streams

Eighty-seven species of chironomid larvae were collected from streams in the Big Thicket area of southeast Texas. Samples of leaf debris, wood debris, and sand were taken from the streams and the larvae occupying the substrates were analyzed. Four subfamilies were represented including Tanypodinae (12 species), Diamesinae (2 species), Orthocladiinae (30 species), and Chironominae (43 species). Dominant species included Lopescladius sp., Polypedilum ? convictum, Polypedilum ? halterale, Cladotanytarsus sp. group A, Rheotanytarsus sp., and Tanytarsus sp. 2. A brief account of the habitat and the distribution of each species encountered during this study is given.