Patterns of pupal mortality in field populations of Hydropsyche and Cheumatopsyche (Trichoptera: Hydropsychidae)

SUMMARY. 1. Up to 40% of hydropsychid pupal cases (from three stations on the Credit and Humber Rivers, Ontario, Canada) contained insects already dead when collected; chironomid infestation accounted for up to 82% of total mortality within a taxon from any one station. The remaining mortality appeared to be due to siltation.
2. For all taxa ( Cheumatopsyche Wallengren and four species of Hydropsyche Pictet), and at all stations, prepupae suffered significantly more chironomid-related mortality than did fully-developed pupae.
3. Chironomid infestation generally affected all species of Hydropsyche equally; at some stations, Cheumatopsyche pupae appeared to suffer less chironomid-related mortality than did co-existing Hydropsyche species.
4. Chironomid infestation affected a greater proportion of pupae at the station where the density of pupal cases (per sampling quadrat) was greatest.
5. Vertical distribution of the pupation site had no apparent influence on mortality attributed to either siltation or chironomid infestation.
6. Chironomid infestation varied seasonally; it was greatest in May and July-August at an upstream station, and peaked in June at the downstream stations.
7. Mortality attributed to siltation was relatively constant for all stages and taxa, at all stations, throughout the sampling programme.     

Impact of flooding on the densities of selected aquatic insects

Data from a four-year study of five aquatic insect species,Hydropsyche betteni, H. morosa, H. bronta, Isonychia bicolor, andEphoron leucon, were utilized to evaluate the impact of a 60-year flood and a few lesser floods. The survey began in August, 1984 and was terminated in October, 1987 with the 60-year flood occurring in November, 1985. Four sampling sites were established on the South River and six quantitative samples were taken each month from each site. Gauging stations on the South River provided accurate discharge data for the sampling sites and useful historical data. Densities for the five species were utilized in the evaluation of the floods. The importance of timing is pointed out, that is, floods that occur very close together or near the end of the life cycle of an insect make it difficult to evaluate floods as disturbances. The importance of life history traits, such as behavior and egg diapause, are discussed in respect to floods. Densities were reduced to less than 50% of their average values immediately after the 60-year flood for the threeHydropsyche spp. and at three sites forI. bicolor. Ephoron leucon showed no response to the 60-year flood. Densities of the four impacted species returned to previous levels in the following generation. The 60-year flood was considered a disturbance in the near term but not for more than one generation.     

A population model for diapausing multivoltine insects under asymmetric cannibalism

Pupa-eating cannibalism occurs naturally in several insect species. Byasa alcinous is a multivoltine species of Red-bodied Swallowtail butterfly found in East Asia, which diapauses as pupa over the winter and whose larvae cannibalize eggs and pupae. We investigate the effects on population dynamics of increasing the asymmetric cannibalistic attack rate of a general insect species in different environmental conditions. We do this by theoretically formulating a generalized system of univoltine and bivoltine larvae over two generations in the spring and summer months. We predict that a lack of resources over the summer can force the population to become entirely univoltine, unless the second-generation bivoltine larvae increase their cannibalistic attack rate, and consume the diapausing pupae from the first generation. The model shows that under extreme environmental conditions, the persistence of univoltine larvae is favoured when faced with the threat of extinction. The model also predicts the conditions for the coexistence of both univoltine and bivoltine larvae, and the degree to which they can both coexist, which decreases as the resource in the second generation increases. This work provides the grounding for future theoretical and experimental consideration of the role of cannibalism in determining insect voltinism.     

Variability of photosensitive period and voltinism among populations of a butterfly,Ypthima multistriata,inhabiting similar latitudes and altitudes

In Ypthima multistriata Butler (Lepidoptera: Nymphalidae), there are univoltine and bivoltine populations in adjacent areas with similar climatic conditions. A previous study revealed that larvae of both univoltine and bivoltine populations diapause under a constant short day (i.e., a constant short light period; L13:D11), but not under a constant long‐day condition (L16:D8). However, in both types of populations, adults of an overwintering generation appear and oviposit in June and soon thereafter larvae hatch. Therefore, the younger larvae (at least the first instars) of both types of populations experience a long day; nevertheless, the larvae of univoltine populations diapause in nature. To resolve this inconsistency, we set up two hypotheses: (1) the photosensitive stage of larvae is the second instar or later, and (2) the photosensitive stage of univoltine populations is later than that of bivoltine populations. To test these hypotheses, we performed rearing experiments with two univoltine populations and two bivoltine ones. The results indicated that the photosensitive stage was the second or third instar and that the photosensitive stage was later in one univoltine population than in the two bivoltine populations. Larvae of the other univoltine population diapaused under all conditions. The former result supports our hypothesis, and the latter result indicates that the response to photoperiod is different among univoltine populations. In addition, larval development was slower in one univoltine population than in the bivoltine populations, which also delays the timing of the diapause decision in this univoltine population. Larvae that experienced a long day during the first and middle instars but experienced a short day at the end of their larval stage developed faster than larvae that experienced a constant long day. This may be an adaptation to enable emergence before the start of a cold season that is unsuitable for reproduction.     

Asymmetric resource competition in a filter-feeding stream insect (Hydropsyche siltalai; Trichoptera)

SUMMARY. 1. Field experiments in a lake outlet stream were carried out on filter-feeding larvae of the caddisfly Hydropsyche siltalai Döhler, to assess whether microhabitat quality, establishment and growth rate is affected by position (upstream—downstream) within a dense aggregation of larvae.
2. Artificial substrates holding high-density aggregations of hydropsychid larvae were used. Marked III-instar H. siltalai larvae were implanted either in the upstream end or in the downstream end of an aggregation and recovered after 17 days.
3. Larvae recovered from the downstream end of an aggregation were smaller than those that had been implanted in the upstream end.
4. Fewer larvae had settled in the downstream end of aggregations compared to the exposed upstream part.
5. Naturally colonizing H. sitalai larvae were, in contrast to implanted larvae, more numerous behind aggregations. Small (first and second instar) Hydropsyche angustipennis (Curtis) and/or H. pellucidula (Curtis) larvae were more numerous in front of aggregations.
6. Current velocities, measured with a microcurrent velocity meter, and density of drifting prey, were significantly lower behind aggregations of hydropsychid larvae. Food availability decreased by about 50% behind aggregations.     

不同家蚕品系的耐热性特征

研究了家蚕Bombyx mori 3个品系(Pure Mysore,NB4D2和CSR2）5龄幼虫和蛹在不同温度（35,38和40℃）下的耐热性,采用Probit分析测定了它们在各温度下的LT50值和置信限。结果表明：多化性品系Pure Mysore在高温下的存活率高于两个二化性品系NB4D2和CSR2,而两个二化性品系中NB4D2表现出更好的耐热性。家蚕幼虫接触38℃高温6 h和40℃高温3 h后,其血淋巴中出现90,70和29 kDa的热激蛋白条带。在恢复过程中,NB4D2和CSR2的血淋巴中未见29 kDa蛋白条带,而Pure Mysore幼虫的血淋巴中29 kDa蛋白仍然表达。当幼虫置于高温下时,血淋巴中90和70 kDa蛋白表达,但是检测不到29 kDa蛋白。研究认为热激蛋白表达与热带家蚕不同品系的耐热性以及与同一品系不同发育阶段的耐热性具有相关性。     

Neuroendocrine regulation of seasonal morph development in a bivoltine race (Daizo) of the silkmoth, Bombyx mori L

We investigated the neuroendocrine regulation of the development of seasonal morphs in a bivoltine race (Daizo) of the silkmoth, Bombyx mori, by decerebration, the transplantation of brain-suboesophageal ganglion (Br-SG) complexes and the injection of active neuropeptides. When brains were removed from fresh pupae destined to develop into summer morphs (SD pupae) by embryonic and larval exposures to short days at low temperature, the pupae developed into autumn or intermediate morphs. However, in pupae destined to develop into autumn morphs (LD pupae), the operation did not show an effect on seasonal morph development. Br-SG complexes were excised from fifth-instar LD and fifth-instar SD larvae 2 days after larval ecdysis and were transplanted into the abdomen of SD larvae of the same age. The Br-SG complexes of LD larvae, but not the Br-SG complexes of SD larvae, shifted the host's seasonal morph development toward the autumn morph. Furthermore, when treated with crude pupal SGs extract and diapause hormone (DH), fresh SD pupae developed into autumn or intermediate morphs, respectively. Possibly the development of seasonal morphs in the silkmoth, B. mori, is regulated by a novel function of DH. Alternatively, DH may act on the imaginal wing disks at an earlier stage than on the ovaries.     

Mortality in reared hydropsychid pupae (Trichoptera: Hydropsychidae)

Cases containing pupae of Hydropsychidae (Trichoptera) were collected from sampling-stations along the length of the Credit and Humber Rivers, Ont., and reared at 18°C. Mortality was high; about 33% of the cases produced adults. Up to 24% of collected cases had been infested with chironomid larvae. Within a station, emergence success and mortality due to chironomid infestation were about the same for the species of Hydropsyche Pictet present; Cheumatopsyche Wallengren suffered less chironomid-related mortality than Hydropsyche. There were significant between-station differences in chironomid-related mortality for H. sparna Ross, H. bronta Ross, H. morosa Hagen, and H. slossonae Banks. Chironomid-related mortality was lowest for pupae from upper Credit R. stations, highest for pupae collected from a lower Credit R. station. Pupae from all Humber R. stations suffered about the same amount of chironomid-related mortality. Chironomid infestation was significantly higher for prepupae than for pupae.     

Ontogenetic patterns and genetic variation in Anopheles (Anopheles) intermedius Chagas, 1908 and Anopheles (Anopheles) mattogrossensis Lutz & Neiva, 1911 (Diptera: Culicidae) in the Brazilian amazon

Changes in the expression of genes were observed during development in populations of Anopheles (Anopheles) intermedius and Anopheles (Anopheles) mattogrossensis. Esterase showed seven zones of activity: EST1 was present in all developmental stages of both species; EST2 was observed only in larvae of A. intermedius and larvae and pupae of A. mattogrossensis, with greater activity in pupae; EST3 and EST5 were present in all developmental stages, with greater intensity in larvae; EST4 and EST6 showed weak activity in larvae of A. mattogrossensis and was not found in A. intermedius. Leucine aminopeptidase showed four zones of activity, of which LAP1 and LAP2 were found in all stages of A. intermedius, with highest activity in larvae, and in larvae only of A. mattogrossensis. LAP3 was detected in all stages of A. mattogrossensis and in larvae only of A. intermedius. LAP4 was detected only in larvae and pupae of A. mattogrossensis, with greater intensity in pupae. alpha-Glycerophosphate dehydrogenase showed a single zone of activity, detected in older fourth-instar larvae and becoming more intense from the pupal stage onwards.     

高温对家蚕三品系血淋巴中糖水平的影响（英文）

家蚕Bombyx mori的两个二化性品系热耐受型NB4D2和热敏感型CSR2均适合于温带气候,而多化性的PM（Pure Mysore) 品系适合于热带气候,将这3种品系5龄幼虫分别置于32℃和36℃的高温下,观察高温对其5龄幼虫至蛹期血淋巴中糖含量及海藻糖酶活性的影响。结果表明： PM幼虫和蛹的死亡率均小于NB4D2和CSR2。在蜕皮期间血淋巴海藻糖水平较高,而葡萄糖水平及海藻糖酶活性较低。32℃和36℃的高温下,幼虫蜕皮期间血淋巴中糖含量及海藻糖酶活性仅在其各自的水平上表现为小幅度的增加。蜕皮后幼虫血淋巴中海藻糖含量显著下降,而葡萄糖含量和海藻糖酶活性显著上升。在较高温度下,蜕皮后幼虫血淋巴中海藻糖含量下降幅度更大,而葡萄糖含量及海藻糖酶活性上升水平也更加显著。25±1℃下取食幼虫血淋巴中葡萄糖含量显著下降,海藻糖含量显著上升;3℃和36℃下PM 和NB4D2取食幼虫血淋巴葡萄糖和海藻糖含量以及海藻糖酶活性增加,而CSR2均减少或降低。吐丝幼虫血淋巴中葡萄糖含量及海藻糖酶活性显著下降,海藻糖小幅度下降。而在较高温度下,耐热型PM 和NB4D2吐丝家蚕血淋巴糖含量含量和海藻糖酶活性明显增加,而热敏感型CSR2的则明显下降。这3种品系蛹发育期的血淋巴糖含量及海藻糖酶活性均下降。在两较高温度下,PM蛹期血淋巴糖和海藻糖酶活性增加,而NB4D2 36℃时增加幅度小于32℃时。对于CSR2,32℃时观察到其血淋巴葡萄糖含量增加,但当环境温度增加到36℃时其血淋巴葡萄糖含量降至正常水平下。然而,当CSR2的蛹置于32℃和36℃时血淋巴海藻糖含量及其酶活性下降,且36℃时下降幅度更大。因此,桑蚕对高温的适应取决于家蚕的品系及发育阶段,并可通过其血淋巴糖及海藻糖酶活性水平进行验证。     

Resistance to thermal stress in preadult Drosophila buzzatii: variation among populations and changes in relative resistance across life stages

Resistance to a short term exposure to a high temperature stress was examined in eggs, larvae and pupae of Drosophila buzzfltii from seven localities. Across development, pupae were most resistant, followed by eggs, and then first and third-instar larvae. Variation among populations for resistance to heat stress was significant in all life stages. However, there was much less variation among populations where measured as eggs and pupae than for both first and third instar larvae. Older larvae showed large changes both in viability and developmental time, while exposure of young larvae to heat stress led to a decline in viability without delayed development. Populations that had the shortest developmental time at 25^oC were relatively the most resistant to heat stress as larvae. High relative resistance at one preadult life stage was not necessarily associated with relatively high resistance at another, or with previous measurements of resistance for adults from these populations. Comparison of populations that were more similar in their pattern of change in resistance across development suggested a relationship with the climate of origin. The possibility that developmental variation in the expression of heat shock proteins may cause variation in resistance to thermal stress for different life stages is discussed.     

Aquatic insects in an estuarine environment: densities, distribution and salinity tolerance

1. Aquatic insects were quantitatively surveyed at five sites along the tidally influenced section of a river-dominated estuary in North Wales. Site 1 was the furthest upstream and was established as a reference site as it was never inundated by salt water. Site 5 was the furthest downstream and was inundated by all incoming tides. Numerically, insects made up 32% of the estuarine invertebrate fauna. 2. Although the densities of most insect taxa decreased towards the estuary mouth, there were significant numbers present downstream for much of the year; for example, in April at site 4 (which was inundated by 81% of all high tides), a mean of 3514 chironomid larvae were recorded per m² of estuary bed. Even at site 5, which was inundated twice daily, there were 747 larvae per m². Among the larger aquatic insects, caddisfly and elmid beetle larvae, together with stonefly nymphs, were consistently taken at site 4 (e.g. maxima of forty-eight caddisfly larvae m^–2 in December and seventy elmids m^–2 in April), although their densities were lower than upstream. 3. There were seasonal shifts in the longitudinal distribution of several taxa, most notably the extension of chironomids down the estuary in April and July, and the concentration of simuliid larvae and mayfly nymphs at site 2 in July. The total freshwater benthos showed a downstream shift between September and December, which was maintained through April and into the summer. The latter was despite peak saltwater inundation (highest tides) in October, November and April. In June and July, when saltwater intrusion was lowest, the ranges of many aquatic insects had contracted to sites 1 and 2. 4. Laboratory experiments showed that virtually all individuals of nineteen species of insects collected from site 1 (freshwater) survived a 4-h immersion in 8.75‰ saltwater (25% strength seawater). Immersion in progressively more saline solutions reduced the survivorship of first the mayflies, followed by the caddisflies Glossosoma conformis and Hydropsyche instabilis. After 4 h in full strength seawater, all specimens of the stonefly Dinocras cephalotes, over half of the Perla bipunctata, and some individuals of nine species of caddisfly were alive. Four species of caddisfly (Sericostoma personatum, Odontocerum albicorne, Potamophylax cingulatus and Adicella reducta) survived a 24-h simulated tidal cycle of immersion. With the exception of P. cingulatus, a few individuals of these caddisfly species survived immersion in full-strength seawater for 24 h. For some individual species there was good agreement between their observed longitudinal distribution in the estuary and laboratory-measured salinity tolerance; however, there was no significant correlation, overall, for the fauna.     

Stream continuum and metabolic rate in the larvae of five species of Hydropsyche (Trichoptera)

The effects of temperature on the metabolic rate of five species of Hydropsyche larvae belonging either to the rhithron (Hydropsyche dinarica, H pellucidula and H siltalat) or to the potamon (H contubernalis and H modesta) have been studied The total amplitude of the metabolic rate between 5 and 25°C is higher in the larvae inhabiting the potamon than those of rhithron (particularly in H siltalat and H dinarica) The shapes of the metabolism temperature curves (M/T curves) of H contubernalis and H modesta differ from each other, although they live in the same habitat and are closely related A comparison with some species of Gammarus suggests a relationship between metabolic rate and the variability of environmental conditions     

Elevationally biased avian predation as a contributor to the spatial distribution of geometrid moth outbreaks in sub‐arctic mountain birch forest

1. Population dynamics and interactions that vary over a species' range are of particular importance in the context of latitudinal clines in biological diversity. Winter moth (Operophtera brumata) and autumnal moth (Epirrita autumnata) are two species of eruptive geometrids that vary widely in outbreak tendency over their range, which generally increases from south to north and with elevation. 2. The predation pressure on geometrid larvae and pupae over an elevational gradient was tested. The effects of background larval density and bird occupancy of monitoring nest boxes on predation rates were also tested. Predation on larvae was tested through exclusion treatments at 20 replicate stations over four elevations at one site, while pupae were set out to measure predation at two elevations at three sites. 3. Larval densities were reduced by bird predation at three lower elevations, but not at the highest elevation, and predation rates were 1.9 times higher at the lowest elevation than at the highest elevation. The rate of predation on larvae was not related to background larval density or nest box occupancy, although there were more eggs and chicks at the lowest elevation. There were no consistent differences in predation on pupae by elevation. 4. These results suggest that elevational variation in avian predation pressure on larvae may help to drive elevational differences in outbreak tendency, and that birds may play a more important role in geometrid population dynamics than the focus on invertebrate and soil predators of previous work would suggest.     

Spatio-Temporal Distribution and Ecological Preferences of Coexisting Hydropsychid Species (Trichoptera) in Two Mediterranean River Basins (S Spain)

The hydropsychids of two Mediterranean river basins in southern Spain (Guadaira and Guadalete) were investigated from January 1988 to January 1989. The distribution of hydropsychids along an environmental gradient related to altitude varied depending on species. Two distinct species assemblages were observed. one located in the lower altitude sites (the “downstream assemblage” comprising Hydropsyche pictetorum, Hydropsyche exocellata and Cheumatopsyche lepida) and the other in the upper-most areas (the “upstream assemblage” comprising Hydropsyche punica, Hydropsyche infernalis, Hydropsyche instabilis), which displayed a statistically significant preference for this type of habitat. Finally, H. pictetorum, selected the lowest sites. From a temporal point of view most species displayed a high variability in density dynamics between sites, suggesting a strong plasticity in life-cycle phenology.     

Acid-induced acute toxicity of aluminium to three species of filter feeding caddis larvae (Trichoptera, Arctopsychidae and Hydropsychidae)

1. Arctopsyche ladogensis , Hydropsyche angustipennis and Hydropsyche siltalai larvae were exposed to nominal aluminium concentrations of 0, 625, 1250, 2500 and 5000 μg Al l^–1 at pH 5.0 for 96 h. Larvae reared at pH 6.4 and without any aluminium treatment were used as controls. Morphological abnormalities in the anal papillae of the larvae were used as the response variable in estimating the median effective concentrations (EC₅₀) of aluminium.
2. No morphological abnormalities were observed in the control larvae. Only a few individuals of A. ladogensis had darkened anal papillae at pH 5.0 without additional aluminium treatment, whereas increasing aluminium concentrations significantly increased the number of individuals in all species displaying darkening and reduction of the papillae.
3. A. ladogensis appeared to be the most sensitive species to increasing aluminium concentrations, as reflected by the significantly lower mean EC₅₀ value for this species compared with those of H. siltalai and H. angustipennis . H. angustipennis larvae were the most tolerant to aluminium.
4. The results indicate that interspecific differences in sensitivity to aluminium may be a key factor influencing the guild structure of filter feeding caddis flies in acidified streams. The results also imply that toxic effects of aluminium on filter feeding caddis larvae occur due to the impairment of normal osmoregulation processes via damage to the ion-regulatory organs.     

Acid-induced acute toxicity of aluminium to three species of filter feeding caddis larvae (Trichoptera, Arctopsychidae and Hydropsychidae)

1. Arctopsyche ladogensis , Hydropsyche angustipennis and Hydropsyche siltalai larvae were exposed to nominal aluminium concentrations of 0, 625, 1250, 2500 and 5000 μg Al l^–1 at pH 5.0 for 96 h. Larvae reared at pH 6.4 and without any aluminium treatment were used as controls. Morphological abnormalities in the anal papillae of the larvae were used as the response variable in estimating the median effective concentrations (EC₅₀) of aluminium.
2. No morphological abnormalities were observed in the control larvae. Only a few individuals of A. ladogensis had darkened anal papillae at pH 5.0 without additional aluminium treatment, whereas increasing aluminium concentrations significantly increased the number of individuals in all species displaying darkening and reduction of the papillae.
3. A. ladogensis appeared to be the most sensitive species to increasing aluminium concentrations, as reflected by the significantly lower mean EC₅₀ value for this species compared with those of H. siltalai and H. angustipennis . H. angustipennis larvae were the most tolerant to aluminium.
4. The results indicate that interspecific differences in sensitivity to aluminium may be a key factor influencing the guild structure of filter feeding caddis flies in acidified streams. The results also imply that toxic effects of aluminium on filter feeding caddis larvae occur due to the impairment of normal osmoregulation processes via damage to the ion-regulatory organs.     

The microdistribution of some lotic insect predators in relation to their prey and to abiotic factors

SUMMARY. 1. The microdistribution of three species of insect predators in a Swedish stream was assessed using a multivariate statistical approach. Both abiotic factors and factors pertaining to the prey community were included in the analysis.
2. The factors most strongly correlated to the distribution of large Dinocras cephalotes were the densities of case less caddis larvae ( Wormaldia sp. and Hydropsyche siltalai ) and the median weight of stonefly prey. For small D. cephalotes , the density of H. siltalai and the percentage of moss cover were most important. Isoperla grammatica showed a significant correlation to blackfly density. Rhyacophila nubila occurred predominantly in patches with high prey biomass and with high densities and median weight of case less caddis larvae.
3. It was concluded that the quantity and quality of the prey, such as size, availability and species, influenced the predators'microdistribution. The distributional pattern differed between species of predators and was probably related to their different hunting strategies.     

Coexistence in a guild of filter feeding caddis larvae: do different instars act as different species?

Summary Guild structure and coexistence of filter feeding caddis larvae was studied in three lake-outlet streams in northern Finland. Natural stones were used as sampling units, and for each stone measurements of six microhabitat variables were taken. Species and species instar relationships in the multivariate microhabitat space were analyzed by a method based on Principal Components Analysis. Seven species of filtering caddis larvae were found at the study sites, but detailed analysis was restricted to the four most abundant ones (Polycentropus flavomaculatus, Hydropsyche angustipennis, H. pellucidula, H. saxonica). P. flavomaculatus was the microhabitat generalist of the guild, whereas all the hydropsychids were narrowly specialized in at least one larval instar. In all species, different instars utilized the microhabitat somewhat differentially. Moss content and Froude number were significantly different between instar microhabitats in all comparisons. Ontogenetic niche changes not only separated species instars from each other, but also profoundly changed the biotic as well as abiotic environment of the species at different phases of larval development. This may have important effects on the dynamics of interacting species and, consequently, on the guild structure. While some of the more classical models of coexistence may also be relevant for understanding coexistence in this guild of sessile stream insects, ontogenetic niche changes clearly need to be taken into consideration in future studies of guild structure and species interactions of filter feeding caddisfly larvae.     

Some effects of organic pollution on the distribution and seasonal incidence of Chironomidae in riffles in the River Cole

SUMMARY. The effects of a sewage effluent discharge into the River Cole, Birmingham, were determined by regular collections of water and biological samples from six comparable stations, one above and five below the sewage effluent. The effluent reduced the dissolved oxygen concentration and increased the ammonia, orthophosphate and BOD concentrations in the water. The effects were much more severe during the summer.
The Chironomidae were very important constituents of the benthic macroinvertebrate community at the stations downstream of the effluent. Larval densities of over 30,000 m⁻² were recorded. Eleven species were common and of these Chironomus riparius was the most tolerant. There was considerable variation in the seasonal incidence of the different species. Brillia longifurca was most abundant in the spring while Cricotopus bicinctus was most abundant in the summer. Brillia longifurca, Paratrichocladius rufiventris, Prodiamesa olivacea, Micropsectra atrofasciata and Eukiefferiella claripennis had three peaks in numbers of larvae during the year.
The increase in the polluted state of the river in the summer resulted in changes in the chironomid populations. Some were suppressed, e.g. E. claripennis , while C. riparius extended its range and achieved maximum abundance further downstream during the summer.