Effects of fenvalerate on the net-spinning behaviour of Hydropsych siltalai (Döhler) (Trichoptera: Hydropsychidae)

The effects of fenvalerate exposure on the net-spinning behaviour of Hydropsyche siltalai were examined in a laboratory study. The larvae were exposed to nominal pulse-doses of 0.25 and 0.5 μg fenvalerate l-1. Nets were collected and examined for anomalies after four days of exposure to fenvalerate. Additional nets were collected after another four day of exposure. The fenvalerate dissipated rapidly from the water column, and since only two doses of fenvalerate were given, the larvae were exposed to two pulse-doses of fenvalerate rather than to a constant concentration. In the 0.5 μg l-1-treatment the net-spinning behaviour was significantly affected, expressed as an increased mesh-opening and a decreased symmetry of the nets. No significant effects of fenvalerate exposure on the net-spinning behaviour were detected in the 0.25 μg l-1-treatment. Thus, with the conditions given in this experiment, exposure to fenvalerate starts to affect the net-spinning behaviour of Hydropsyche siltalai at a concentration between 0.25 and 0.5 μg l-1. The use of net-anomalies and Hydropsyche as bioindicators for monitoring pollutants in stream ecosystems are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

New Species of Macrogynoplax Enderlein 1909 from North Brazil (Plecoptera,Perlidae, Acroneuriinae)

Three new species of Macrogynoplax Enderlein 1909, M. delicata, M. pulchra and M. poranga are described. They were collected in Manaus, Amazon State.     

Insights into species diversity of the genus Hydropsyche Pictet, 1834 (Hydropsychidae,Trichoptera) from the Lake Kinneret catchment (Israel)

Species identification based on larval stages of aquatic insects in Israel is difficult, given the paucity of taxonomic studies. In order to gain deeper understanding of biological processes in Israel's freshwater ecosystems and to develop a bioindication system, species have to be known and characterised at all life stages. Here, we applied an integrative morphological and genetic approach to characterise caddisflies of the genus Hydropsyche Pictet, 1834 from the Lake Kinneret catchment. Seventeen sites in the Lake Kinneret catchment were sampled in spring/summer 2015 and 2016. For 77 hydropsychid larvae and two adult specimens of H. yahfufah Malicky, 2001, we analysed a 658 bp fragment of the mitochondrial COI gene and compared the results of different genetic species delimitation methods to observed morphological variation. Our results suggest the presence of at least five species. This study is an important first step towards assessing stream biodiversity of a yet largely understudied region and highlights advantages of integrative taxonomic approaches.     

Life cycle of Rhyacophila fasciata Hagen, 1859 and Hydropsyche saxonica McLachlan, 1884 in a Dinaric karst river system

Life cycles of Rhyacophila fasciata Hagen, 1859 and Hydropsyche saxonica McLachlan, 1884 were investigated in a Dinaric karst river system. Benthic samples were taken monthly from January to December 2005. Environmental variables were measured simultaneously. Larval stages were defined using head capsule widths. As only instars 2–5 were collected in the field, the head width of first instar larvae was extrapolated using Dyar's rule. R. fasciata showed an extended emergence and recruitment, whereas in H. saxonica a typical univoltine cycle with summer and early autumn emergence was observed. Canonical correspondence analysis was used to define the relationship between environmental variables and larval stages. H. saxonica larval instars were distributed along temporal and nutrient gradients at all sampling sites, but differences were observed among sampling sites. The larval instars, prepupae and pupae of R. fasciata were distributed along water depth and oxygen concentration gradients, but temporal and temperature gradients were less important.     

Net-building behaviour,tolerance and development of two caddisfly species from the river Rhine (Hydropsyche contubernalis and H. pellucidula) in relation to the oxygen content

Summary Tolerance, growth and development of H. contubernalis and H. pellucidula were analyzed at different O₂-concentrations to determine the species specific potency amplitude in relation to O₂-concentration. In addition netbouilding behaviour was compared at different O₂-concentrations and current velocities. Under anaerobic conditions slightly greater tolerance was observed in H. contubernalis than in H. pellucidula. But at a higher O₂-concentration H. contubernalis showed a distinctly higher O₂-deficiency tolerance than H. pellucidula in relation to net-building activity, growth and development. In addition, more than 50% of H. contubernalis instars built capture nets with regular meshes at an O₂-saturation of only 30% (15°C). High growth rates were also found at 50% O₂-saturation and more than half the larvae developed into imagos. In addition to diminished net-spinning activity the mean growth rate started to decrease at an O₂-saturation of 70% to 38% and the development into an imago was not possible in H. pellucidula. Because H. contubernalis corresponds to a regulative type, being able to maintain a high level of netbuilding activity, growth rate and development over a wide range (50% to 100% O₂-saturation). On the other hand H. pellucidula corresponds to a conform type, because physiological efficiency decreases rapidly with falling O₂-concentration, so that development into an imago is no longer possible below 85% O₂-saturation. Positive correlation between net-spinning activity and tested current velocity between 10 cm/s and 25 cm/s (15°C) was found in H. pellucidula. H. contubernalis showed no change in net-building activity, over this range of current velocity. H. contubernalis can be classified as an euryoecious species with a great potency amplitude in relation to O₂-concentration and current velocity. The high tolerance to O₂-deficiency conditions probably allowed the early recolonization of the Mittel-and Niederrhein when a distinct O₂-deficit (mean 29%, max 56%) could still be measured. H. contubernalis can be considered a bioindicator of O₂-deficiency situations. Undisturbed development of H. pellucidula in this section of the river requires a further improvement in O₂-content.     

Insular radiation of the genus Hydropsyche (Insecta,Trichoptera: Hydropsychidae) Pictet, 1834 in the Philippines and its implications for the biogeography of Southeast Asia

Aims To record and elucidate the phylogeny and biogeography of a species swarm of the genus Hydropsyche (Insecta, Trichoptera) in the Philippines. All species belong to the hamifera group. Location The Philippines and neighbouring areas. Methods A phylogenetic analysis based on variation of morphological characters of the male phallic apparatus. Results The species swarm is differentiated into three clades of different age. Conclusion Alternative dispersal and vicariance hypotheses are considered in an attempt to explain the colonization of the Philippine archipelago and the subsequent ramification of the group. The vicariance hypothesis based on the late Miocene accretion of continental fragments to the Philippines appears to be the most parsimonious. The evolution of the swarm occurred on the Philippines. Later on species dispersed to Borneo, Sulawesi and the Moluccas. The species swarm has undergone an adaptive radiation which enabled the simultaneous occurrence of species in the same streams.     

Life history and production of filter-feeding insects on stone dikes in the lower Mississippi River

Population and production dynamics of two filter-feeding macroinvertebrates, the caddisfly Hydropsyche orris and the midge Rheotanytarsus sp., were examined in the lower Mississippi River Miles 510–515. Samples were collected from September to November 1987, May to December 1988, and March to May 1989 from stone dikes that protrude into the river. Developmental synchrony was high among individuals in both populations, and seasonal changes in the relative abundance of instars indicated bivoltine and trivoltine life cycles for H. orris and Rheotanytarsus sp., respectively. The size frequency method was used to estimate production (P) and biomass (B) of each cohort in each population. P/B ratios for spring and fall cohorts of H. orris equaled 4.5 and 3.7. Spring, summer, and fall cohorts of Rheotanytarsus sp. had P/B ratios of 4.0, 4.7, and 4.1, respectively. Annual production, estimated as the sum of cohort production values, of the H. orris and Rheotanytarsus sp. population equaled 10.1 and 0.359 g m^–2 (dry weight). Annual P/B ratios equaled 10.8 and 16.1 for the H. orris and Rheotanytarsus sp. populations, closely matching values expected for bivoltine and trivoltine populations, respectively. Annual production of H. orris is in the low end of the range of published estimates for other lotic hydropsychid populations inhabiting coarse substratum in warm, lowland rivers of medium size or small, trophically enriched streams. Annual production of Rheotanytarsus sp. is the first such estimate based on a simultaneous assessment of life cycle and production. Given the lack of naturally occurring gravel and cobble substrate in the lower Mississippi River, stone dikes are an especially important habitat for H. orris and Rheotanytarsus sp.     

Ecosystem engineering by larvae of net-spinning stream caddisflies creates a habitat on the upper surface of stones for mayfly nymphs with a low resistance to flows

1. Field and laboratory experiments were conducted to examine the effect of larval retreats of the net‐spinning stream caddisfly Hydropsyche orientalis on abundances on flow exposed stone surfaces of nymphs of the mayfly Ephemerella setigera, which prefer slow flow conditions, and to determine whether the construction of retreats ameliorated the habitat and made it more suitable for E. setigera. 2. In a field experiment, artificial substrates with retreats of H. orientalis had higher E. setigera abundances than substrates lacking retreats. In addition, abundances of E. setigera nymphs increased significantly with those of H. orientalis larvae on the upper surface of boulders in streams. 3. The drift loss of E. setigera from plates, with and without retreats, was investigated along a current velocity gradient in a laboratory channel experiment. Nearly all E. setigera nymphs remained on the plates with retreats, even at the highest current velocity. In contrast, on the plates without retreats, the drift loss of E. setigera nymphs increased as the current velocity increased. 4. These results suggested that the habitat amelioration by H. orientalis retreats provided a refuge location for E. setigera nymphs and increased their abundances on stone surfaces exposed to flow forces.     

The Larva of Hydropsyche tabacarui Botosaneanu, 1960 (Trichoptera: Hydropsychidae), Including a Re-description of the Female

The larva of Hydropsyche tabacarui Botosaneanu, 1960 is described and compared with the morphologically very similar larva of H. tibialis McLachlan, 1884. Information for the identification of both species is given and some zoogeographical and ecological notes are presented. In addition, the female of H. tabacarui is re-described.