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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]

During the Pleistocene, when the climate was wetter and cooler, aquatic habitats in the Great Basin of western North America were much more extensive and connected. As the climate warmed over the last 10 000 years, many of these habitats dried but others remained as isolated springs and inland lakes. The isolation of desert springs and lack of dispersal between populations of non-vagile species (e.g. fish, spring snails) has led to genetic differentiation and speciation. However, the extent to which vagile species of aquatic insects disperse from spring to spring is unknown. We examined the population genetics of two caddisflies, Hesperophylax designatus (Limnephilidae) and Lepidostoma ojanum (Lepidostomatidae) that occur in isolated springs in Nevada and eastern California to determine the extent of their dispersal from spring to spring. Mitochondrial DNA sequences indicate that the populations of L. ojanum are isolated and that the populations represent management units. In contrast, H. designatus individuals are flying from spring to spring and their populations are connected by dispersal. Disturbance impacts (e.g. grazing by ungulates, water extraction) that eliminate poor dispersers (e.g. L. ojanum) locally may result in permanent losses of genetic diversity; this is less likely with broader dispersers such as H. designatus. [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]