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SUMMARY 1. Oviposition site selection was studied in three trichopteran species; an undescribed species of Hydatophylax (Limnephilidae), Onocosmoecus unicolor (Limnephilidae) and Neophylax rickeri (Uenoidae), in two Coastal Range streams in California, U.S.A. 2. Hydatophylax sp. egg masses were generally found at or above the water surface on substrata near the bank in pools, where undercut banks, overhanging vegetation and rocks shaded attachment sites and provided wind protection. Onocosmoecus unicolor females deposited their egg masses exclusively above the water on moist emergent wood. The egg masses of N. rickeri were almost exclusively found in high velocity areas of riffles, where females oviposited under water and attached their egg masses to the submersed undersides of unembedded, protruding stones with large emergent surfaces. 3. For Hydatophylax sp. and N. rickeri , a hierarchical selection scheme is proposed in which females use cues at three different spatial levels (stream, stream subunit, substratum) to choose oviposition sites. Females of O. unicolor seemed to choose at only two different levels of spatial resolution (stream, substratum). 4. The formation of large aggregations of egg masses in N. rickeri and O. unicolor suggests that females actively choose oviposition sites where conspecific egg masses are already attached. The clustering of egg masses may minimise the risk of predation through the dilution effect, because egg masses of N. rickeri and O. unicolor are both attacked by dipteran predators. 5. Females of the three Trichoptera species studied are able to make a clear choice of oviposition site in the heterogeneous stream environment. In comparison with other stream microhabitats, these are characterised by stable and relatively predictable environmental conditions during the time of egg development, which is seen as the main selective pressure leading to the observed egg-laying behaviour. [ABSTRACT FROM AUTHOR]

Two species in the caddisfly genus Gumaga (Sericostomatidae) are currently recognized in North America: Gumaga nigricula (McLachlan, 1871) and Gumaga griseola (McLachlan, 1871). Ecological and morphological studies over the last 20 years indicated that both species were either extremely variable or that morphologically cryptic species were unknowingly being included in the studies. The study reported here examined whether genetic characters (as measures of reproductive isolation and genetic differentiation) could resolve the taxonomic issues concerning Gumaga , and consequently provide insight into the observed ecological and morphological variation. Allozyme electrophoresis was used to examine the genetic relationships among larvae of Gumaga collected from five streams and two springbrooks in northern California. For each specimen, 18 enzymes representing 21 presumptive gene loci were scored. Genetic variability was high at all but one site: 14.3-47.6% of the loci were polymorphic (3-10 loci per site) and heterozygosity averaged 5.9-20.7%. Six genetically distinct groups of individuals were identified (i.e., Gumaga types A, B, C, D, E, F). Mean Nei's genetic distances between groups ranged from 0.371 (type A versus type B) to >1.0 (type F versus types A, B, D, or E). The high degree of genetic differentiation among groups is maintained even when the groups are in close proximity (e.g., Gumaga types A and E at the same site and Gumaga types A, B, and C within the same drainage basin). In addition, previous studies have found evidence of premating mechanisms that limit interbreeding among Gumaga types A, B, and D. Thus, it appears that these six groups represent reproductively isolated species rather than genetic variants of one or two species. Extensive morphological and genetic studies are necessary to clarify taxonomic relationships within the genus Gumaga, but the results of this and other genetic analyses of aquatic insects illustrate the potential insight that this approach can provide to taxonomic, behavioral, and ecological studies. Furthermore, these results also illustrate how unusual (and what is often perceived as interesting) ecological variability observed for a single species may in fact reflect the presence of morphologically cryptic species. [ABSTRACT FROM AUTHOR]

Reports the results of field observations and experiments conducted in Big Sulphur Creek over a 4-year period that were designed to examine the relationship between wet-season hydrolic disturbance and subsequent density of late-instar (H. borealis). Assesses the impact of competition on this population under different hydrologic disturbance regimes. Annual variability; Aquatic insect; More.

Describes a multivariate, predictive model based on the reference-condition approach for the Fraser River catchment in British Columbia. Study area and sampling sites; Assemblage metrics; Taxonomic resolution.

We investigated relationships among insecticides and aquatic invertebrate communities in 22 streams of two soy production regions of the Argentine Pampas over three growing seasons. Chlorpyrifos, endosulfan, cypermethrin, and lambda-cyhalothrin were the insecticides most frequently detected in stream sediments. The Species at Risk (SPEAR) pesticide bioassessment index (SPEAR pesticides ) was adapted and applied to evaluate relationships between sediment insecticide toxic units (TUs) and invertebrate communities associated with both benthic habitats and emergent vegetation habitats. SPEAR pesticides was the only response metric that was significantly correlated with total insecticide TU values for all three averaged data sets, consistently showing a trend of decreasing values with increasing TU values (r 2 = 0.35 to 0.42, p-value = 0.001 to 0.03). Although pyrethroids were the insecticides that contributed the highest TU values, toxicity calculated based on all insecticides was better at predicting changes in invertebrate communities than toxicity of pyrethroids alone. Crustaceans, particularly the amphipod Hyalella spp., which are relatively sensitive to pesticides, played a large role in the performance of SPEAR pesticides , and the relative abundance of all crustaceans also showed a significant decreasing trend with increasing insecticide TUs for two of three data sets (r 2 = 0.30 to 0.57, p-value = 0.003 to 0.04) examined. For all data sets, total insecticide TU was the most important variable in explaining variance in the SPEAR pesticides index. The present study was the first application of the SPEAR index in South America, and the first one to use it to evaluate effects of pesticides on invertebrate communities associated with aquatic vegetation. Although the SPEAR index was developed in Europe, it performed well in the Argentine Pampas with only minor modifications, and would likely improve in performance as more data are obtained on traits of South American taxa, such as pesticide sensitivity and generation time. [ABSTRACT FROM AUTHOR]