Dicosmoecus Gilvipes Research Articles

Mild temperatures differentiate while extreme temperatures unify gene expression profiles among populations of Dicosmoecus gilvipes in California.

Accurately predicting the effects of future warming on aquatic ectotherms requires an understanding how thermal history, including average temperature and variation, affects populations of the same species. However, many laboratory studies simplify the thermal environment to focus on specific organismal responses and sacrifice environmental realism. Here, we paired laboratory-based transcriptomic RNA-seq analysis to identify thermally responsive genes with NanoString analysis of a subset of those genes to characterize natural field-based variation in thermal physiology among populations. We tested gene expression responses of three populations of field-acclimatized larval caddisflies (Dicosmoecus gilvipes) from streams in different eco-regions (mountain, valley, and coast) following exposure to current and future summertime temperatures. We hypothesized that distinct thermal histories across eco-regions could differentiate populations at baseline “control” levels of gene expression, as well as gene expression changes in response to daily warming and heat shock. Population-specific patterns of gene expression were apparent under the control and daily warming conditions suggesting that local acclimatization or local adaptation may differentiate populations, while responses to extreme temperatures were similar across populations, indicating that response to thermal stress is canalized. Underlying gene co-expression patterns in the daily warming and heat shock treatments were different, demonstrating the distinct physiological mechanisms involved with thermal acclimatization and response to thermal stress. These results highlight the importance and limitations of studies of the thermal biology of wild-caught organisms in their natural environment, and provide an important resource for researchers of caddisflies and aquatic insects in general.

Phylogeographic comparison of five large-bodied aquatic insect species across the western USA

Glacial legacy, barriers to migration, and dispersal abilities are important determinants of intraspecific genetic diversity. Genetic comparisons can elucidate the distribution of genetic variants among populations, but for many groups of organisms the concordance of population genetic structure and historical refugia among co-occurring species remains unclear. We compared phylogeographic histories of 4 stoneflies (Calineuria californica, Hesperoperla pacifica, Pteronarcys californica, and Pteronarcys princeps) and 1 caddisfly (Dicosmoecus gilvipes) across their species ranges. Study species had large body and wing sizes that suggest strong flying ability and dispersal potential. Nevertheless, riverine habitat restrictions and mating behaviors can inhibit dispersal. We used mitochondrial and nuclear gene sequences to examine population genetic structure relative to potential past and present barriers to dispersal in the western USA. North–south population genetic structure was present for each species but was more pronounced for 2 stoneflies (C. californica and P. californica) and the caddisfly. For these 3 species, phylogenies indicated concordant clades north and south of San Francisco Bay, a large, saltwater estuary in California. Basal phylogenetic nodes and regional centers of haplotype diversity suggested common historical refugia in northern California or southern Oregon, similar to that found in previous studies of salamanders. For 1 stonefly (C. californica) and the caddisfly, distinct populations in the Sierra Nevada Mountains suggested potential barriers to gene flow. The presence of population genetic structure suggests vulnerability to loss of intraspecific diversity under climate change scenarios, particularly for populations at high elevations.

Microdistributional Variability of Larval Caddisflies in Mediterranean-Climate Streams in Northern California

ABSTRACT. Knowing how physical and biogenic habitat characteristics affect microspatial variability of larval caddisflies is important to understanding potential population distributions and local species assemblages. We show that larval caddisfly densities and assemblages vary between study reaches and streams on the Angelo Coast Range Reserve in northern California and that species abundance patterns are associated with specific habitat variables. Dicosmoecus gilvipes and Psychoglypha spp. were most dense in 4th-order reaches of the south fork of the Eel River (SFE) and rare or absent in shallow 2nd- and 1st-order reaches of the Elder and Fox Creek tributaries, respectively. Multidimensional scaling (MDS) suggested D. gilvipes densities were associated with water depth, as microdistributions were restricted to depths >40 cm. Microdistributions were also associated with Rivularia-dominated algal patches, but it is doubtful grazing D. gilvipes tracked these cyanobacteria. Psychoglypha spp. were typically ...

The caddisflyDicosmoecus gilvipes: making a case for a functional role

AbstractMost caddisfly larvae build cases of silk and a variety of collected materials. Multiple functions, including protection from predators, resistance to entrainment by high flows, and improved respiration, have been suggested for caddisfly cases. We investigated the functional role of cases built by Dicosmoecus gilvipes, a limnephilid caddisfly. In this species, the 1st- through 4th-instar larvae build cases with plant material and attach Douglas-fir needles as lateral extensions that resemble vanes on an arrow. We tested whether the lateral extensions and entire case deterred predators by manipulating lateral extensions and case presence for larvae exposed to large steelhead trout. No larva with a case (with or without lateral extensions) was consumed during the experiment, whereas all larvae without a case were consumed. We tested whether lateral extensions provided stability against overturning and entrainment by manipulating presence of lateral extensions and subjecting larvae to turbulent flow ...

SEASONAL REASSEMBLY OF A RIVER FOOD WEB: FLOODS, DROUGHTS, AND IMPACTS OF FISH

Eighteen years of field observations and five summer field experiments in a coastal California river suggest that hydrologic regimes influence algal blooms and the impacts of fish on algae, cyanobacteria, invertebrates, and small vertebrates. In this Mediterranean climate, rainy winters precede the biologically active summer low‐flow season. Cladophora glomerata, the filamentous green alga that dominates primary producer biomass during summer, reaches peak biomass during late spring or early summer. Cladophora blooms are larger if floods during the preceding winter attained or exceeded “bankfull discharge” (sufficient to mobilize much of the river bed, estimated at 120 m3/s). In 9 out of 12 summers preceded by large bed‐scouring floods, the average peak height of attached Cladophora turfs equaled or exceeded 50 cm. In five out of six years when flows remained below bankfull, Cladophora biomass peaked at lower levels. Flood effects on algae were partially mediated through impacts on consumers in food webs. In three experiments that followed scouring winter floods, juvenile steelhead (Oncorhynchus mykiss) and roach (Lavinia (Hesperoleucas) symmetricus) suppressed certain insects and young‐of‐the‐year fish fry, affecting persistence or accrual of algae positively or negatively, depending on the predator‐specific vulnerabilities of primary consumers capable of suppressing algae during a given year. During two post‐flood years, these grazers were more vulnerable to small predators (odonates and fish fry, which stocked steelhead always suppressed) than to experimentally manipulated, larger fish, which had adverse effects on algae in those years. During one post‐flood year, all enclosed grazers capable of suppressing algae were consumed by steelhead, which therefore had positive effects on algae. During drought years, when no bed‐scouring winter flows occurred, large armored caddisflies (Dicosmoecus gilvipes) were more abundant during the subsequent summer. In drought‐year experiments, stocked fish had little or no influence on algal standing crops, which increased only when Dicosmoecus were removed from enclosures. Flood scour, by suppressing invulnerable grazers, set the stage for fish mediated effects on algae in this river food web. Whether these effects were positive or negative depended on the predator‐specific vulnerabilities of primary consumers that dominated during a given summer.

Transmission of Ehrlichia risticii, the agent of Potomac horse fever, using naturally infected aquatic insects and helminth vectors: preliminary report.

Ehrlichia risticii, the agent of Potomac horse fever (PHF), has been recently detected in trematode stages found in snail secretions and in aquatic insects. Based on these findings, horses could conceivably be exposed to E. risticii by skin penetration with infected cercariae, by ingestion of infected cercariae in water or via metacercariae in a second intermediate host, such as an aquatic insect. In order to test this hypothesis, horses were challenged with infectious snail secretions and aquatic insects collected from a PHF endemic region in northern California. Two horses stood with their front feet in water harbouring E. risticii-infected cercariae, 2 horses drank water harbouring E. risticii-infected cercariae, and 6 horses were fed pools of different aquatic insects harbouring E. risticii-infected metacercariae. In this preliminary study, only the one horse infected orally with mature caddisflies (Dicosmoecus gilvipes) developed the clinical and haematological disease syndrome of PHF. The agent was isolated from the blood of the infected horse in a continuous cell line and identified as E. risticii by characterisation of the 16S rRNA gene. Therefore, E. risticii is maintained in nature in a complex aquatic ecosystem and transmission to horses can occur through accidental ingestion of insects such as caddisflies containing infected metacercariae. At present, the small number of horses used in this study does not exclude other insects and free trematode stages as potential sources of infection.

Effects of Recreational Activities on the Distribution of Dicosmoecus gilvipes in a Mountain Stream

Abundances of the larval caddisfly Dicosmoecus gilvipes and epilithic algae were compared at 9 sites (5 exposed to extensive recreational activity and 4 with minimal activity) in Quartzville Creek, Oregon. Recreational impacts on caddisfly densities were apparent for instars 3-5, but effects were greater on earlier instars than later instars. In 1995, sites with low human use had significantly higher densities of D. gilvipes than those sites exposed to intense recreation. Chlorophyll a biomass was not correlated with either D. gilvipes densities or intensity of human activity. In February 1996, an 85-y flood event forced closure of the study area to the public throughout the 2nd sampling season. Recreational impacts from 1995 were apparent at more localized spatial and temporal scales than were effects of flooding in 1996. The flood reduced D. gilvipes densities by 83% (±23% SE) and chlorophyll a biomass by 41% (±28% SE) across all sites. These results emphasize the need for additional studies on how multiple recreational activities impact lotic food webs.

Influence of grazer type and abundance on plant-herbivore interactions in streams

Grazer-periphyton interactions were investigated in 11 laboratory streams holding a range of densities of three herbivore taxa during a 32-d experiment. Effects of grazers on algae were strongest with Dicosmoecus gilvipes caddisflies, intermediate with Juga silicula snails, and weakest with Baetis spp. mayflies. Algal standing crop, export, and gross primary production declined logarithmically with increasing grazer density. Algal turnover rate, however, increased with grazer abundance. At high densities of all grazers, responses in most algal parameters converged, suggesting that high grazing pressure, regardless of taxon, will similarly affect periphyton. Growth of both Dicosmoecus caddisflies and Juga snails was density-dependent, with the highest growth rates occurring at the lowest densities. Caddisflies displayed high growth rates but low efficiency in resource use. Snails had lower growth rates but were more efficient in resource use. The coexistence of Dicosmoecus and Juga, or other competing herbivores, in natural streams may be related to these fundamental differences in life history strategies.

Stream periphyton response to grazing and changes in phosphorus concentration

Grazing by the large caddisfly larva, Dicosmoecus gilvipes (Trichoptera; Limnephilidae), drastically reduced periphyton biomass in laboratory channels at a current velocity of 20 cm s−1. Reduction in biomass as chl a and AFDW ranged from 88 to 93% and 82 to 85%, respectively. On average, grazing rate increased with in-channel SRP (soluble reactive phosphorus) content from 6 to 10 µg 1−1. Grazing rates averaged 25.9–29.3 µg chl a m−2 d−1 and 10.8–12.2 µg chl a mg−1 d−1 based on area and grazer biomass, respectively, with most variability among treatments being due to the grazing effect. Grazing tended to shift the algal community increasingly to filamentous blue-green algae regardless of enrichment. After three weeks, Phormidium comprised over 61% of the community in grazed treatments but only 35% in ungrazed treatments. The stalked diatom Gomphonema comprised only 4% of the grazed community, but 11% in the three ungrazed channels with similar values for Scenedesmus. A model that includes grazing was calibrated to the data and produced a reasonable expectation of periphyton biomass over a range in SRP concentrations. While the model with constant grazer abundance predicts a gradually increasing grazed biomass as SRP increases, grazer production in natural streams may actually increase to accommodate the increased food production.

The Impact of Dipper, Cinclus mexicanus, Predation on Stream Benthos

Stream sections from which American dippers (Cinclus mexicanus) were excluded contained higher densities of the limnephilid caddisfly Dicosmoecus gilvipes than exclosure-control sections after 16 d in Wheeler Creek, Utah, USA. Dipper exclusion produced no detectable effect on the density of large Baetis mayflies on exposed surfaces, while the effect of dipper exclusion on small Baetis depended on water depth. Exposed heptageniid mayflies were more abundant in dipper exclosures. Densities of Dicosmoecus and mayflies did not differ between exclosure-controls and unmanipulated stream sections. Perhaps in response to dipper predation, Dicosmoecus occupied relatively deep microhabitats in Wheeler Creek. The estimate of Dicosmoecus conssumption by dippers from our experiment parallels estimates from studies of the food habits and bioenergetics of European dippers

Plant—herbivore interactions in streams near Mount St Helens

SUMMARY1. In four separate field experiments near Mount St Helens (Washington, U.S.A.) during 1986, the grazing effects of two large benthic herbivores, tadpoles of the tailed frog Ascaphus truei and larvae of the caddisfly Dicosmoecus gilvipes, were investigated using streamside channels and in‐stream manipulations. In the experimental channels, abundances of periphyton and small benthic invertebrates declined significantly with increasing density of these larger herbivores.2. In eleven small, high‐gradient streams affected to varying degrees by the May 1980 eruption, in‐stream platforms were used to reduce grazing by A, truei tadpoles on tile substrates. Single platforms erected in each tributary and compared to grazed controls revealed only minor grazing effects, and no significant differences among streams varying in disturbance intensity (and, consequently, tadpole density). However, results probably were confounded by high variability among streams in factors other than tadpole abundance.3. Grazing effects were further examined in two unshaded streams with different tadpole densities, using five platforms per stream. In the stream with five tadpoles m−2, grazing reduced periphyton biomass by 98% and chlorophyll a by 82%. In the stream lacking tadpoles, no significant grazing effects were revealed. Low algal abundance on both platforms and controls, and high invertebrate density in that stream (c. 30000m−2) suggests that grazing by small, vagile invertebrates was approximately equivalent to that of tadpoles.4. The influence of large benthic herbivores on algal and invertebrate communities in streams of Mount St Helens can be important, but reponses vary spatially in relation to stream disturbance history, local environmental factors, and herbivore distributional patterns and abundance.

Periodicity in Mate Attraction and Flight Activity of Three Species of Caddisflies (Trichoptera)

Diel periodicities of mate attraction and flight activity were examined for three caddisfly species (Insecta:Trichoptera) that use female sex pheromones to attract conspecific males: Dicosmoecus gilvipes (Hagen) (Limnephilidae), Gumaga nigricula (McL.) (Sericostomatidae), and Gumaga griseola (McL.). Live females of D. gilvipes attracted males during the night, with 58% of the males being captured in the first hour after sunset. Live females of G. griseola attracted 97% of the males during the hour before sunrise whereas live females of G. nigricula attracted 85% of the males 2-4 h after sunrise. For all three species, the periodicity of male response to female pheromone was the same as the periodicity of male response to live females. In laboratory chambers, male and female D. gilvipes flew during the mate attraction period but generally not at other times. Male flight for G. nigricula and G. griseola was generally most intense during periods of mate attraction, and was reduced during non-attraction periods. In contrast, females of both Gumaga species were relatively sedentary during periods of mate attraction. The presence of circadian rhythms that govern the periodicity of flight was demonstrated for all taxa and sexes except females of D. gilvipes. Light intensity and air temperature influenced the amount of flight activity but not flight periodicity. The temporally brief and coordinated activities of these short-lived adults may serve to conserve metabolic resources, contribute to their reproductive success, and maintain reproductive isolation.

Temporal patterns of grazer‐periphyton interactions in laboratory streams

SUMMARY. 1. The snail Juga silicuta (500 m−2) and the caddisfly Dicosmoecus gilvipes (50 m−2) were introduced into separate laboratory streams on days 1, 9, 16 and 28 of algal development. The mayfly Baetis spp. (500 m−2) was introduced on days 1 and 16, and two streams did not receive grazers. We assessed the interaction between succession in the pcriphyton, herbivore type and time of encounter in a 40‐day experiment.2. In ungrazed streams, the chlorophyte Scenedesmus obliquus was the most abundant early colonizer. The relative abundance of diatoms increased after day 9, and at day 40 the algal assemblage consisted of a thick mat of diatoms and S. obliquus with an overstorey of filaments of the chlorophyte Stigeoclonium tenue. In general, introductions of grazers at any stage altered this pattern by removing biomass, accelerating the replacement of S. obliquus by diatoms, and suppressing the growth of filaments. Grazing also reduced the relative abundance of the larger diatom Nitzschia oregona but increased the relative abundance of the smaller adnate diatoms Nitzschia frustulum var. perpusilla and Navicula minima.3. Dicosmoecus decreased algal biomass and altered successional trajectories to a greater degree than either Juga or Baetis. Dicosmoecus rapidly grazed the entire substrate, whereas Juga and Baetis only cleared patches in the assemblages. Little alteration in algal development was observed in the Baetis streams after day 16, probably because (he periphyton assemblages attained a size and structure that prevented effective grazing by Baetis.4. The patchy grazing patterns of Juga and Baetis resulted in more diverse algal assemblages than either the Dicosmoecus grazed or ungrazed streams. In natural streams, the temporal and spatial pattern of grazing relative to the developmental stage of the periphyton may contribute to maintaining a mosaic of algal patches in different serai stages.

Behavioral Changes in the Herbivorous Caddisfly Dicosmoecus gilvipes (Limnephilidae)

Behavioral patterns differ among third-, fourth-, and fifth-instar Dicosmoecus gilvipes larvae. Feeding, crawling, resting, case building, and interactions were observed among all instars, but time spent in each category varied according to larval instar, hunger, and type of algae available. Larvae fed one-third of the time. Third-instar larvae fed longer on diatoms, whereas fourth and fifth instars fed longer on filamentous assemblages. Third-instar larvae crawled faster than other instars, fourth instars spent the most time case building, and fifth instars rested more than others. Resting and case building were often associated activities. Interactions among individuals were infrequent; neither aggression nor cannibalism were observed. The variety and changes in behavior exhibited by D. gilvipes may affect grazing levels on algal resources and influence possible competitive interactions. Behavioral studies that encompass developmental patterns of organisms provide critical contexts for studies of ecological processes in streams.

Alterations in periphyton characteristics due to grazing in a Cascade foothill stream

SUMMARY 1. In situ experiments were conducted in a Washington stream to quantify the effects of grazing by a caddisfly larva, Dicosmoecus gilvipes (Trichoptera: Limnephilidae), and a mayfly nymph, Nixe rosea (Ephemeroptera: Heptageniidae) on periphyton biomass, structure, and function.2. Dicosmoecus gilvipes reduced periphyton biomass from 92 mg m−2(as mean chlorophyll a) to 33 mg m−2. The grazed assemblage was less diverse and composed of smaller, closely attached diatoms, whereas there was a higher proportion of overstorey and filamenttius algae in the diverse, ungrazed periphyton.3. By maintaining the periphyton community as a thin layer of diatoms, grazing by D. gilvipes appeared to promote a healthier, more vigorous community relative to the ungrazed mat, which became senescent in the latter part of the experiment.4. Nixe rosea had little measurable effect on any characteristics of the periphyton measured. These nymphs apparently preferred small diatoms, which resulted in only micro‐scale alterations in periphyton characteristics that were difficult to detect.5. Biomass accrual of ungrazed and grazed periphyton was described by the logistic growth equation. Loss of biomass due to grazing by D. gilvipesor to senescence and sloughing were incorporated in the model to account for changes in grazed and ungrazed periphyton. respectively. Proposed mechanisms which described biomass accumulation were largely sup ported by model predictions.

Effects of Herbivore Type and Density on Taxonomic Structure and Physiognomy of Algal Assemblages in Laboratory Streams

Four densities of a snail (Juga silicula) and a caddisfly (Dicosmoecus gilvipes) were introduced into separate laboratory streams, and their effects on algal biomass and community structure were monitored for 32 d. Tiles in an ungrazed control stream were covered by thick algal mats by day 32, and were composed primarily of Scenedesmus spp., Characium, and a variety of diatoms. Biomass and community structure of algal assemblages in the stream with the lowest density of snails were very similar to those in the control stream. In the other streams with snails, an inverse relationship developed between algal biomass and snail density after day 16. By day 32, the algal assemblages in the streams with high snail densities were dominated by adnate diatoms (e.g., Achnanthes lanceolata), and basal cells and short filaments of Stigeoclorium tenue. In contrast to the streams with snails, algal biomass was relatively low in all streams with caddisflies. The differences in algal biomass and structure between the streams with the lowest and highest densities of caddisflies were much smaller than those between streams with the lowest and highest densities of snails. On day 32, the taxonomic and physiognomic structure of the algal assemblages in all the streams with caddisflies resembled that in the streams with higher densities of snails. Scanning electron micrographs showed that even at the highest densities, neither snails nor caddisflies could completely remove the algal assemblage. It is concluded that grazing can substantially influence algal growth form and assemblage physiognomy in lotic ecosystems.

Effects of Herbivore Type and Density on Chemical Composition of Algal Assemblages in Laboratory Streams

The chemical composition of algal assemblages in laboratory streams was determined 3 and 27 d after adding snail (Juga silicula) and larval caddisfly (Dicosmoecus gilvipes) grazers. Three days after the herbivores were introduced (day 8 of algal growth), the fatty acid and amino acid profiles among algal assemblages were similar. Substantial differences were noted after 4 wk (day 32 of algal growth), however, especially with respect to the 16:0, 16:1, 16:3, 18:3, and 20:5 fatty acids. On day 32, algal assemblages subjected to zero or 125 snails/stream (66/m²) had higher levels of glycine, leucine, isoleucine, tyrosine, and the 16:3 and 18:3 fatty acids than assemblages exposed to 500 snails/stream (250/m²), 50 caddis/stream (25/m²), or 200 caddis/stream (100/m²). On the other hand, assemblages subjected to high grazing pressure (i.e., 500 snails/stream, 50 and 200 caddis/stream) had higher levels of alanine, glutamic acid/glutamine, and the 16:0, 16:1, and 20:5 fatty acids than algae exposed to zero or 125 snails/stream. These data provide detailed information on the food quality of lotic algae and may serve as a starting point for future research in this field.

Effects of Three Herbivores on Periphyton Communities in Laboratory Streams

The effects of grazing on algal assemblages by three different stream herbivores, the mayfly Centroptilum elsa, the snail Juga silicula, and the caddisfly Dicosmoecus gilvipes, were studied during a 48-d experiment in six laboratory streams. Compared with ungrazed control streams, grazing by Centroptilum (500/m2) modified algal community structure slightly but had little effect on periphyton biomass and chlorophyll a. Grazing by Juga (350/m2) reduced periphyton biomass and chlorophyll a by nearly 50%, but increased the rate of primary production by up to 25%. Juga also prevented significant accumulation of cyanophytes and some diatom species. Grazing by Di- cosmoecus (200/m2) reduced periphyton biomass and chlorophyll a to less than 5% of the ungrazed levels, but primary production declined by only 50%. Only adnate algal cells and short filaments persisted on substrates grazed by Dicosmoecus. Algal export rates were increased by all three her- bivores. Modification of algal growth patterns by both consumption and dislodgement, and dampening of temporal fluctuations were key mechanisms by which these herbivores altered periphyton com- munities. Primary production was stimulated by low rates of grazing by Juga in the laboratory streams, possibly as a result of increased light intensity in lower strata of the periphyton or removal of senescent algal cells. Algal assemblages displayed both community-level responses (e.g., biomass, production) and species-level responses (e.g., taxonomic composition) that should be considered in other studies of stream herbivory.

Stream microhabitat selectivity, resource partitioning, and niche shifts in grazing caddisfly larvae

Microhabitat selectivity, resource partitioning, and niche shifts in five species of grazing caddisfly larvae (Glossosoma califica, G. penitum, Dicosmoecus gilvipes, Neophylax rickeri, and N. splendens) were quantified by underwater measurement of microhabitat availability and utilization in three northern California streams. The microhabitat parameters water depth and velocity and rock size, roughness, and slope were measured. Comparisons of habitat available to habitat used revealed significant selection for at least two microhabitat parameters by each population, with depth and velocity being the most important. Comparisons of habitat used by different species showed significant partitioning of at least two microhabitat parameters at each site, with depth being partitioned at all sites. Non-parametric discriminant analysis revealed significant microhabitat partitioning on a multivariate level at two sites. Comparisons of habitat used at different sites quantified a major niche shift by D. gilvipes in its preference for riffles versus pools. Size-selective predation by dippers (Cinclus mexicanus) and steelhead (Salmo gairdneri gairdneri) is proposed as a hypothesis to explain the observed resource partitioning and niche shift.

Bionomics of Dicosmoecus gilvipes (Trichoptera: Limnephilidae) in a Large Western Montane River

Dicosmoecus gilvipes (Hagen) has a 2-year life cycle in the upper Flathead River, Montana. First-instar larvae appeared in spring and grew to fourth instar by late summer. Larvae typically entered fifth instar during late summer or autumn and spent the winter months attached to the undersides of large rocks in apparent diapause. Fifth-instar larvae were again active as water temperatures warmed above 1 C in March. In midsummer, fifth-instar larvae again attached their cases to the undersides of rocks and entered a 4- to 6-week prepupal diapause prior to metamorphosis. Adults emerged from late August through October. Early-instar larvae occurred primarily in depositional areas at the edge of riffles or in pools and backwater areas. Late-instar larvae were most frequently observed on and within the rubble substrate of lotic erosional zones, yet outside turbulent riffles. The change in habitat from depositional to erosional zones was coincident with decreased river discharge. The 2-year life cycle is explained in terms of temperature and food quantity-quality relationships.