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.     

Chironomid (Diptera: Chironomidae) communities in six European glacier-fed streams

1. A study on glacial stream ecosystems was carried out in six regions across Europe, from Svalbard to the French Pyrenees. The main aim was to test the validity of the conceptual model of 38 with regard to the zonation of chironomids of glacier‐fed rivers along altitudinal and latitudinal gradient. 2. Channel stability varied considerably, both on the latitudinal and altitudinal scale, being lowest in the northern regions (Svalbard, Iceland and Norway) and the Swiss Alps. Water temperature at the upstream sites was always <2 °C. 3. There was a prominent difference in taxonomic richness between the Alpine and the northern European regions, with a higher number of taxa in the south. In all regions, the chironomid community was characterized by the genus Diamesa and the subfamily Orthocladiinae. Of a total of 63 taxa recorded, two (Diamesa bertrami and Orthocladius frigidus) were common in all the regions except Svalbard. 4. On the basis of cluster analysis, seven distinct groups of sites were evident amongst glacial‐fed systems of the five regions (Pyrenees excluded). This classification separated the glacier‐fed streams on geographical, latitudinal and downstream gradients. 5. Canonical Correspondence Analysis (CCA) of environmental variables was carried out using 41 taxa at 105 sites. Slope, water depth, distance from source, water temperature and the Pfankuch channel stability index were found to be the major explanatory environmental variables. The analysis separated Diamesinae and typical upstream orthoclads from the other chironomids by low temperature and high channel instability. 6. In all six regions, Diamesa was present closest to the glacier. Within 200 m of the glacier snout, other genera of Diamesinae were found together with Orthocladiinae. Pioneer taxa like Diamesa species coexisted with later colonizers like Eukiefferiella minor/fittkaui in relatively unstable channels. 7. The longitudinal succession of chironomid assemblages across altitudinal and latitudinal gradients in glacial streams followed the same pattern, with similar genera and groups of species. The general aspects of the conceptual model of 38 were supported. However, Diamesa species have wider temperature limits than predicted and other Diamesinae as well as Orthocladiinae colonize metakryal habitats.     

Ecological effects of urban stormwater runoff on benthic macroinvertebrates inhabiting the Green River,Massachusetts

Although it has been demonstrated that urban stormwater can alter the quality of receiving waters, the corresponding impact on aquatic biota remains essentially undocumented. A year-long intensive study, therefore, was implemented to monitor and describe the ecological effects exerted by urban runoff on benthic macroinvertebrates.Rock-filled, basket-type artificial substrates deployed periodically in nonurban and urban river reaches yielded collections of macroinvertebrates that furnished data for: (1) species diversity (the Brillouin index, H), (2) hierarchical diversity, (3) major taxa composition, and (4) collection dissimilarity at the species level.The overall results from these four analytical procedures strongly indicate that the macrobenthic community became progressively disrupted downstream in the urban reach. The high degree of correspondence between the known sources of urban runoff and the observed effects on the benthic community are forceful arguments that urban runoff is the causal agent of disruption. The impact is not confined to periods following heavy rains. Instead the pollutants appear to remain in the system. The stress imposed by them was most acute during the summer low flow and was probably localized in or near the stream bed.To assess the impact of urban runoff on an aquatic ecosystem, physical, chemical, and biological monitoring should routinely consider the stream bed microzone. Urban runoff pollutant loading standards must take into account the apparent long-term residence of pollutants in the substrate and the associated stress of summer low flows.     

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.     

Comparisons of benthic invertebrates between riffles and pools

Benthic species assemblages in upstream and downstream ends of riffles and in pools were investigated seasonally in the first five orders of an alluvial gravel stream with distinct pool and riffle channel form. Riffles comprised < 10% of stream area and were separated by pools with extensive bedrock substrate (ca. 15–85% of total surface area) which was scoured during periodic high flow. Virtually all taxa were more abundant in riffles than in pools, except chironomids which were more equally distributed. Inconsistent results were obtained for upstream-downstream comparisons within riffles. Intermittent headwater reaches (orders 1 & 2) which supported half as many taxa retained this pattern during periods of flow, although riffles at these sites were dry from mid-June to mid-November. Pools which contained more gravel, indicating less disturbance during high flow, had a richer assemblage of benthic species than other pools. Many invertebrates in pools may have been there as a result of drift from their preferred riffle habitats, but the presence of gravel in the pools indicates less intense flow disturbance during floods, provides protection from the mild scouring that does occur during floods, and provides refugia from predators.     

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.     

Biological and molecular responses of Chironomus riparius (Diptera,Chironomidae) to herbicide 2,4-D (2,4-dichlorophenoxyacetic acid)

2,4-Dichlorophenoxyacetic acid (2,4-D) is an agricultural contaminant found in rural ground water. It remains to be determined whether neither 2,4-D poses environmental risks, nor is the mechanism of toxicity known at the molecular level. To evaluate the potential ecological risk of 2,4-D, we assessed the biological parameters including the survival rate, adult sex ratio of emerged adults, and mouthpart deformities in Chironomus riparius after long-term exposure to 2,4-D. The larvae were treated with 0.1, 1 or, 10 μg L^? 1 of 2,4-D for short- and long-term exposure periods. The sex ratio was changed in C. riparius exposed to only 10 μg L^? 1 of 2,4-D, whereas mouthpart deformities were observed as significantly higher in C. riparius exposed to 0.1 μg L^? 1 of 2,4-D. Survival rates were not significantly affected by 2,4-D. Furthermore, we evaluated the molecular and biochemical responses of biomarker genes such as gene expression of heat shock proteins (HSPs), ferritins and glutathione S-transferases (GSTs) in C. riparius exposed to 2,4-D for 24 h. The expressions of HSP70, HSP40, HSP90 and GST levels in C. riparius were significantly increased after exposure to a 10 μg L^? 1 concentration of 2,4-D, whereas ferritin heavy and light chain gene expressions were significantly increased at all concentrations of 2,4-D exposure. Finally, these results may provide an important contribution to our understanding of the toxicology of 2,4-D herbicide in C. riparius. Moreover, the 2,4-D-mediated gene expressions may be generated by 2,4-D is the causative effects on most probable cause of the observed alterations. These biological, molecular and morphological parameters and the measured parameters can be used to monitor 2,4-D toxicity in an aquatic environment.     

Temporal distribution of larval Chironomidae (Diptera) in experimental rice fields in Penang,Malaysia

The distribution and abundance of chironomid larvae were investigated in experimental rice fields at the Bukit Merah Agricultural Experimental Research Station, Penang, Northern Malaysia. The mean density of chironomid larvae during the period of the study (including two cultivation seasons) was 121 larvae m^?2. Chironomus kiiensis (48.6%) was the most abundant species, while four other species, Polypedilum trigonus (4.8%), Tanytarsus formosanus (22.6%), Tanypus punctipennis (13.9%), and Clinotanypus sp. (10.1%) occurred less frequently, although they were present during all wet phases of rice cultivation. Generally, water depth, rice plant height, conductivity, and nitrate–nitrogen content of the water only weakly influenced the abundance of the larvae. Other environmental parameters such as pH, dissolved oxygen, daytime water temperature, total suspended solids, phosphate, and sediment total organic matter did not significantly affect larval populations. The community structure of chironomids in this rice agroecosystem followed the dynamic changes of the field including agronomic practices, patterns of water availability, and phases of rice plant growth.     

Impact of arsenic and antimony contamination on benthic invertebrates in a minor Corsican river

The chemical and biological characteristics of a Corsican river that drains contaminated waters and sediment from an abandoned realgar mine were studied. The concentrations of pollutants such as As and Sb were found to be notably high. For example, in the Presa River, downstream the realgar mine, the mean As concentrations in the water and in the sediment were 3010 g 1^-1 and 9450 g g^-1 respectively. Species richness and abundance of benthic invertebrates decreased downstream the As mine. The disappearance of oligochaetes, leeches and a rarity of mayfly populations have been evidenced. On the contrary, a large increase in species belonging to stoneflies and gastropods was found. Some species like Baetis cyrneus, Ephemerella ignita, Sericostoma clypeatum and Ibisia marginata were more sensitive to As and Sb concentrations while others species like Ancylus fluviatilis, Isoperla insularis, Hydropsyche cyrnotica, Caenis luctuosa and Silonella aurata were less sensitive. The benthic invertebrates show different reactions in this contaminated environment, which could be explained by their feeding behaviours and certain morphological characteristics.     

The relative contributions of refugium types to the persistence of benthic invertebrates in a seasonal snowmelt flood

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Food preferences of tanypodinae larvae (Diptera: Chironomidae)

Analyses of the gut contents of larvae of three species of Tanypodinae, collected from four sites in north-east England and Scotland, invariably showed small particles (1–10 µm²), predominantly of detritus, to be more abundant than large particles (10–100 µm²), mostly algae and diatoms. No animal remains, such as carapaces, head capsules and chaetae, or vascular plant fragments were found in any of the intestines. In contrast, food-choice and growth experiments suggested that animal food (particularly Tubificidae and Chironominae larvae) was important in the tanypod diet. In the food-choice experiments, six different foods offered to small (4–7 mm long) and to large (8–12 mm long) larvae of Procladius choreus Meigen, were chosen in the following order: live Tubificidae spp.; detritus; live Chironominae larvae; a mixture of algae and diatoms; live Ostracoda spp.; and live Cladocera spp. However, when the results of the individual choices were examined, it was clear that the small larvae had consumed greater amounts of the small types of food (i.e. detritus, algae and diatoms) in comparison to the large larvae. In the growth experiment, those larvae of P. choreus reared solely on Tubificidae, detritus or Chironominae larvae thrived, while those fed on algae and diatoms, ostracods or cladocerans grew more slowly and fewer survived the experimental period.It was concluded that although Tanypodinae larvae are primarily predators with definite food preferences in ideal foraging conditions, in adverse conditions they will utilize a range of available stand-by foods, the most important of which appears to be detritus.     

The colonisation of experimental ponds by Chironomidae (Diptera)

The colonisation and succession of chironomids in a newly‐dug gravel pit habitat was investigated using replicate experimental ponds sampled during the summers of 1977 and 1978. In 1977 larvaeand emerging adults were collected, whilst in 1978 only adults were sampled. Benthic sampling showed the larval communities to be predominated by Chironomus spp. whilst trapping of adults showed that this group accounted for only 4% of the emergence. This difference is attributed to the selective retention of the larger Chironomus larvae by the sieve used to screen benthos samples. The pioneer chironomid communities in the ponds are compared using similarity and diversity indices on adult emergence data. These showed that the pond communities were remarkably uniform in 1977, the first year of their existence, due to the predominance of Tanytarsus gracilentus. In 1978 the communities were much more variable. The community structure changed within the two years, with equitability increasing rapidly to that characteristic of a much more mature habitat. These successional changes are attributed to a reduction in uniformity of the habitat resulting from the growth of aquatic macrophytes.     

Parachironomus Lenz from China and Japan (Diptera,Chironomidae)

Members of the genus Parachironomus Lenz known from China and Japan are revised, and a key to their male adults is given. Parachironomus poyangensis sp. n. is described in this life stage. Parachironomus frequens (Johannsen) and Parachironomus monochromus (van der Wulp) are recorded from China for the first time, thus are redescribed from Chinese specimens. Parachironomus kamaabeus Sasa & Tanaka and Parachironomus toneabeus Sasa & Tanaka are new junior synonyms of Parachironomus frequens. Three Chinese or Japanese species formerly placed in Parachironomus are transferred to other genera, resulting in the new combinations Cryptochironomus inafegeus (Sasa, Kitami & Suzuki), Demicryptochironomus (Irmakia) lobus (Yan, Sæther, Jin & Wang), and Microchironomus lacteipennis (Kieffer). Chironomus sauteri Kieffer, Parachironomus kisobilobalis Sasa & Kondo and Parachironomus kuramaexpandus Sasa are removed from Parachironomus; the last of these three denotes a valid species of uncertain generic placement, the first two are nomina dubia.     

Determining the density dependence of immigration and emigration of benthic stream invertebrates: theoretical considerations

Simple mathematical models are formulated to describe density independent and density dependent dispersal. These models clarify hypotheses of density dependence and may be manipulated easily to suit particular applications. The models demonstrate that the initial composition of a species aggregate must be controlled before valid conclusions can be drawn about the density dependency of the aggregate's dispersal. Stochastic models of emigration are derived to assess the power of particular experimental designs and statistical techniques to discriminate a known form of density dependent emigration. Contribution No. 369, Great Lakes Research Division, University of Michigan Contribution No. 369, Great Lakes Research Division, University of Michigan     

Drift and benthic invertebrate responses to stepwise and abrupt increases in non-scouring flow

We conducted two experiments to assess drift and benthic invertebrate responses to stepwise and abrupt changes in non-scouring flow in gravel-bed experimental streams. Intuitively, a stepwise flow increase should allow aquatic invertebrates more time to seek refuges than would an abrupt increase. We hypothesized that abrupt flow increases would result in larger increases in taxon richness and in the number of invertebrates in the drift, and a larger decrease in benthic density than would stepwise flow increases. Two kinds of drift response to flow increases were observed in the stepwise experiment: (1) no response (e.g. Caenissp. [Ephemeroptera] and Sphaeriidae [Pelecypoda]); (2) threshold response of some aquatic (e.g. Crangonyx pseudogracilis[Amphipoda]) and semiaquatic (e.g. Ormosiasp. [Diptera]) taxa. Drift richness and drift density in both experiments declined after reaching a peak. The peak was reached almost immediately in the abrupt treatment and later in the stepwise treatment. Maximum richness of taxa and taxon composition in the drift were similar in both experiments. Despite significant increases in drift, stepwise and abrupt increases in flow did not have a significant effect on benthic density. However, relative to reference streams, the percentage of total benthic invertebrates in the drift increased 10× in the stepwise experiment and 33× in the abrupt experiment. These non-scouring increases in flow were non-trivial. Our results suggest that several high flow events of the same magnitude (i.e. 2.5–3.0 fold increases) may cause considerable losses of benthic populations to the drift. The rate of increases in flow appears to be important: abrupt increases in flow had a stronger effect on invertebrate drift than did stepwise increases.     

Heterogeneity and Heterofunctionality of Hemoglobins in Bloodworms (Diptera, Chironomidae)

In electrophoretic spectra of hemoglobins of Chironomus species of plumosus group, 3 groups of fractions are arbitrarily identified: fast fractions (mobility of 0.85 and higher), fractions with intermediate mobility (0.58–0.83), and slow fractions (mobility of 0.43 and lower). The most unstable turned out to be the fast fractions; their protein content increased considerably at storage and repeated freezing–thawing of samples. Fractions with the intermediate mobility are the most numerous, have a high specific amount according to the protein content and a high peroxidase activity. The slow fractions in the majority of species were characterized by a low peroxidase activity and high protein content. An interspecies comparison of electrophoretic spectra of hemoglobins has shown that the species that are the most tolerant to oxygen deficiency have the slow fractions with the lowest mobility. The obtained data have allowed suggesting that that the identified groups of hemoglobins are functionally heterogeneous: (1) the fast fractions with mobility of 0.85 and higher are products of degradation of hemoglobins with a higher molecular mass; (2) fractions with intermediate mobility (0.58–0.83) have a high affinity to oxygen and provide its utilization at its very low concentrations in water; (3) the slow fractions with mobility of 0.43 and lower have a high mol. mass and perform the buffer function preventing disturbance of the acid-base equilibrium of internal medium at anaerobiosis.     

Dispersal of adult aquatic Chironomidae (Diptera) in agricultural landscapes

• 1 This study investigates the possible influence of terrestrial landscape structure on the spatial distribution of adult Chironomidae emerging from water bodies in three agricultural areas, each with hedgerow networks, in Brittany (France).
• 2 Using spatially explicit data from 128 yellow pan traps set in pairs at the bottom of hedges throughout the three study areas, we show that landscape structure and heterogeneity must be considered at two different spatial scales.
• 3 At a global scale, distance to water bodies was the main factor explaining the spatial distribution of adult chironomids: both species richness and abundance changed beyond a critical distance to the stream, resulting in different species assemblages of flying insects.
• 4 At a local scale, the abundance of species and individuals at rest in hedges changed with the quality of the hedge (mainly determined by canopy width and cover of the different vegetation layers).
• 5 The density of the hedgerow network, and landscape openness, both influenced the dispersal of chironomid species from water bodies.
• 6 This study, which provides the first estimate of the dispersal capabilities of chironomids in particular landscapes, suggests that the terrestrial environment is an essential component of population dynamics and community structure in aquatic Chironomidae.

     

Bathymetric distribution of some Chironomidae (Diptera) in Rutland Water

The bathymetric distribution of the eight most abundant taxa of chironomid larvae is described from benthic grab samples collected in Rutland Water from May 1977 to April 1979. Cricotopus, Psectrocladius and Endochironomus larvae were generally restricted to water less than 9 m deep. Procladius, Chironomus, Microtendipes, Polypedilum and Tanytarsini larvae were all recorded at depths down to 25 m. However, the highest population densities of the latter five taxa were recorded in shallow water. The results are discussed in relation to the diet of trout and certain management practices at the reservoir. Also described is the application of SPSS (Statistical Package for the Social Sciences) to the analysis of these data.     

Larval morphology and Karyotype of Cladopelma viridula (Diptera, Chironomidae)

The larval morphology and karyotype of Cladopelma viridula are described.