Peter Zwick

Stream habitat fragmentation - a threat to biodiversity

Biodiversity is undisturbed rhithral streams in central Europe is high, with about 1000 resident metazoan species; over 600 insect species occur in the Fulda river (Germany). Longitudinal downstream shift of dominance from rheobiontic to rheophilous and finally to ubiquituos rheoxenic taxa in the potamal is described. Present downstream importance of ubiquituous species probably results from replacement of original potamal communities, present faunas being surrogates. Species losses through human impact are well documented for fish. The case of Plecoptera (10 potamal species either altogether extinct, extinct in Central Europe or extremely endangered) suggests that potamal invertebrates suffered as severe losses as did fish.Human impact on major rivers was so severe also because they occur at distances beyond average dispersal capacity of the fauna, i.e. are widely separate ecological islands, with known risk of species losses. In contrast, faunal exchange between adjacent headwater streams in mountains with intact stream nets is easy, certainly for amphibious insects. However, damage to rhithral streams is becoming increasingly frequent. This fragments stream nets, turning also upper parts of drainage systems into ecological islands, with danger of extinctions. Rhithral biodiversity is thought to be much more endangered by human impact than is presently recognized.

Key to the West Palaearctic genera of stoneflies (Plecoptera) in the larval stage

Abstract An illustrated dichotomous key to larvae of all genera of Plecoptera in the West Palaearctic region (i.e., Europe, Asia Minor and the Palaearctic part of northern Africa) is presented. Brief comments on included species are added for each genus, plus diagnostic details of selected bioindicator species. Two appendices provide a key to larvae of the German species of genus Nemoura and taxonomic notes on selected species and operational taxonomic units in genus Leuctra , respectively.

Emergence, maturation and upstream oviposition flights of Plecoptera from the Breitenbach, with notes on the adult phase as a possible control of stream insect populations

Upstream oviposition flights of several Plecoptera species of the genera Leuctra, Nemoura, Isoperla and Siphonoperla along the Breitenbach, Hesse, Germany are inferred from 1. oviposition occuring upstream from emergence areas; 2. size differences and size-shifts between emerging and egg-laying females; 3. concentration of oviposition in upstream sections of the emergence area. The last point relies on direct catches of egg-laying females with sticky traps, and on over-representation of old, mature females in upstream emergence traps towards the end of, or even after actual emergence periods. Criteria for age class discrimination of the respective taxa are described. The validity of the present and of other indirect evidence for directed adult flights and the significance of adult upstream displacement are discussed. Optical orientation cues are suggested.Females of Leuctra prima and Siphonoperla torrentium are shown to gain 25–50% dry weight by feeding in the terrestrial environment; general information indicates many other Plecoptera may be similar in this respect. Terrestrial adult life is shown to last for 3–8 weeks. This long time, evidence of important flight activity and feeding together suggest that the terrestrial phase is spent as an active adult, the inevitable risks of which may form an important control of population dynamics.

Global diversity of dipteran families (Insecta Diptera) in freshwater (excluding Simulidae, Culicidae, Chironomidae, Tipulidae and Tabanidae)

Today’s knowledge of worldwide species diversity of 19 families of aquatic Diptera in Continental Waters is presented. Nevertheless, we have to face for certain in most groups a restricted knowledge about distribution, ecology and systematic, particularly in the tropical environments. At the same time we realize a dramatically decline or even lack of specialists being able, having the time or the opportunity to extend or even secure the present information. The respective families with approximate numbers of aquatic species are: Blephariceridae (308), Deuterophlebiidae (14), Nyphomyiidae (7), Psychodidae (∼2.000), Scatopsidae (∼5), Tanyderidae (41), Ptychopteridae (69), Dixidae (173), Corethrellidae (97), Chaoboridae (∼50), Thaumaleidae (∼170), Ceratopogonidae (∼6.000), Stratiomyidae (∼43), Empididae (∼660), Lonchopteridae (2), Syrphidae (∼1.080), Sciomyzidae (∼190), Ephydridae (∼1.500), Muscidae (∼870). Numbers of aquatic species will surely increase with increased ecological and taxonomical efforts.

Revision of the Stonefly Family Eustheniidae (Plecoptera), with Emphasis on the Fauna of the Australian Region

The revision includes diagnoses of the family and its subfamilies. Keys to genera and species are provided. Descriptions of known species are supplemented or corrected. Several new synonymies are established and some new species are described. The majority of species in the Australian Region are illustrated, and detailed faunistical data are also presented. The following taxa are recognized: Eustheniidae Tillyard; Eustheniinae Tillyard (= Thaumatoperlinae Tillyard): Neuroperlopsis lilies (N. patris Illies), Thaumatoperla Tillyard (T. robusta Tillyard; T. flaveola Burns & Neboiss; T. alpina Burns & Neboiss; T. timmsi nov. spec.), Eusthenia Gray (=Eustheniopsis Tillyard, nov. syn.) (E. costalis Banks = E. purpurescens Tillyard, nov. syn. . = E. purpurescens extensa Tillyard, nov. syn.; E. lacustris Tillyard = E. spectabilis eulegnica Tillyard, nov. syn.; E. spectabilis Gray = E. lunulata Tillyard, nov. syn., = E. reticulata Samal—not Tillyard! , nov. syn.; E. reticulata (Tillyard), nov. comb.; E. venosa (Ti...

Biometric studies of some stoneflies and a mayfly (Plecoptera and Ephemeroptera)

Aspects of the nymphal/adult developmental change were investigated in biometric studies of several species of Plecoptera: Nemouridae near Schlitz, Hesse, Germany. Preliminary information on the mayfly, Baetis vernus Curtis, is also provided. Nemourid nymphs pass through 3 wing bearing stages before reaching adulthood. Instars can be identified by their characteristic shapes, as expressed by the wing length/head width (WL/HW) ratio. Size does not allow instar discrimination, mainly due to sexual size differences. HW is ca 10% larger in last instar female than in male nemourid nymphs; exuviae shed at the moult to adult represent about 14% of nymphal ash free dry weight (AFDW). Biomass lost with exuviae during the many larval moults should be accounted for in estimates of production. Freshly emerged nemourid females are about 6% larger and 30% heavier than males. The HW/AFDW relationship is the same in both sexes. Through terrestrial feeding during adult life, males double their weight on average. Mature females are up to three times heavier than freshly emerged ones. They invest about 30% of their final AFDW in reproduction.Shape of last instar nymphal Baetis was expressed as the ratio wing length/mesonotum length. It is size-dependent, a characteristic, instar-specific shape may not occur in this mayfly. Nymphal and subimaginal exuviae together represent about 14% of last instar nymphal dry weight. Females of Baetis are about 55% heavier than males. Unlike in Plecoptera, the size/weight (ML/AFDW) relationship differs between sexes.

Plurimodal emergence and plurivoltinism of Central European populations of Nemurella pictetii (Plecoptera: Nemouridae)

SummaryNemurella pictetii Klapálek, 1900 (Plecoptera: Nemouridae) has bi-or trimodal emergence patterns in Central Europe. The emergence threshold temperature is about 8°C. Egg development is direct. The slopes of regressions describing its temperature dependence do not differ significantly between English, Norwegian and German populations, but the intercepts (i.e., the incubation period at 0°C) do. Regular sampling of a benthic population near Schlitz, in Hesse, West Germany, showed that part of the offspring of the first emergence group grew quickly and produced a second emergence peak. The remaining offspring of the first generation grew more slowly and overwintered, together with the offspring of the second emergence peak. This population exhibits partial bivoltinism. The potential for bivoltinism was also shown in laboratory rearings of a German population at a constant 14°C: many eggs yielded normal adults after about 120 days. Larval growth rates were up to 2.2% body length day-1, much higher than for English Nemurella (unimodal emergence), or any other stonefly. The thermal sum (degree-days above 0°C) accumulated between the two emergence peaks, at the German sites studied, resembled cumulated degree-days in a laboratory culture. For an Austrian population with trimodal emergence, degree-days accumulated in the field were lower, suggesting a lower temperature demand and partial trivoltinism. This is the only case of confirmed plurivoltinism in Plecoptera. Nemurella pictetii seems to have lost seasonal life cycle cues, enabling the opportunistic use of favourable local conditions. Population synchrony appears to be regulated by the thermal demand for development and the emergence threshold temperature.

A revision of the Oriental stonefly genus Phanoperla (Plecoptera: Perlidae)

The genus Phanoperla (=Dyaperla Banks, 1939) (Plecoptera: Perlidae: Perlini) is revised and generic diagnoses are provided for adults and larvae. Diagnostic and constitutive characters of the tribe Neoperlini are discussed, and Chinoperla Zwick, 1980, is shown to be the closest relative of Phanoperla. Many past misidentifications of Phanoperla species have been corrected by the use of characters recently recognized as important, namely the structure of the internal genitalia of male and female specimens and particularly the complex pattern of spines on the male penial sac made visible by eversion of this structure, and details of sculpturing of the egg chorion.

The Plecoptera – who are they? The problematic placement of stoneflies in the phylogenetic system of insects

There is no consensus about the relations of Plecoptera with other insects. Very different sistergroup relationships have been proposed in the literature, several of which are discussed. The phylogenetic analysis is hampered by the diversity among Plecoptera. In the literature, traits of particular subgroups of Plecoptera have sometimes been mistaken as typical of the entire order. A plea for revived interest in plecopteran morphology is made in order to document the existing diversity and to establish the ground pattern of important structures for meaningful comparisons with other insects. A possible sistergroup relationship between Plecoptera and the remaining Neoptera, on the one hand, and a sistergroup relationship with the Polyneoptera on the other hand, seem most likely. Suggested close relationships of Plecoptera with Embioptera and Phasmatodea are refuted. Molecular data so far also failed to provide robust phylogenetic hypotheses for the placement of Plecoptera.

The Bornean species of the stonefly genus Neoperla (Plecoptera : Perlidae)

The Bornean species of the perlid genus Neoperla are described. The fauna includes representatives of the clymene‐ and montivaga‐groups. Several species-complexes within these groups are distinguished. Redescriptions of previously named species are based on a study of type material, except for N. variegata. Lectotypes are designated for several species. A number of species known only from females cannot presently be assigned to named species and are given provisional informal letter designations. Named species recognized in this study are: N. rougemonti sp. n.; N.sabah sp. n.; N. theobromae sp. n.; N. parva Banks, 1939; N. edmundsi Stark, 1983; N. starki sp. n.; N. Sarawak sp.n.; N. borneensis (Enderlein,1909) comb, n.; N. naviculata Klapalek, 1909; N. naviculata crux ssp. n.; N. harina Navas, 1929; N. furcifera Klapalek, 1909; N. bilobata sp. n.; N.furcata sp. n.; N. tetrapoda sp. n.; N. securifera sp. n.; N. multilobata sp. n.; N. connectens sp. n.; N. divergens sp. n.; N. variegata Klapalek, 1909 (=N. ...