Contrasting diel activity and feeding patterns of four instars of Rhyacophila dorsalis (Trichoptera)

1. Ontogenetic shifts in prey choice and predator behaviour can affect food‐web structure. Therefore, it is important to establish if the diet and feeding activity differ between life‐stages of the same species. This hypothesis was tested for second, third, fourth and fifth larval instars of Rhyacophila dorsalis by comparing their diel activity and feeding patterns. Second to fifth instars collected from two streams were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks. Food was provided in excess; being organisms living in bryophytes on top of a large stone in each tank, augmented by different‐sized larvae of Ephemeroptera, Simuliidae and Chironomidae. As few first instars for gut analyses were found in the field, the diet of first instars reared in the laboratory was also studied. 2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 50 larvae per instar for each day or night sample). First and second instars fed on the smaller food items with no significant day‐night differences in diet. Gut contents indicated a progressive trend from feeding chiefly at night in third instars to almost exclusively at night in fifth instars. Fourth and fifth instars fed on the larger food items, whilst the diet of the third instar larvae overlapped with that of both the earlier and later instars. 3. Diel activity patterns of single larvae differed between instars but not within each instar (n = 20 larvae per instar). Second instars were active throughout the 24 h, with peaks at dusk, around midnight, dawn and around midday. A similar pattern was shown by third instars but the peak of activity at midday was less than the other three peaks. Prey were captured only during these peaks for both instars. Fourth and fifth instars were most active, and fed only, at night. They used an ambush strategy to capture more active prey at dusk and dawn (e.g. Baetis, Gammarus), and a searching strategy to capture more sedentary prey during the night (e.g. chironomids, simuliids). These experiments provided support for the hypothesis under test. If competition and/or interference occur between instars, then it could be reduced between earlier and later instars because of differences in their diet and diel pattern of feeding activity.     

小石蛾属一新种记述：毛翅目：小石蛾科

本文记述了河南省小石蛾属１新种──钩突小石蛾Ｈｙｄｒｏｐｔｉｌａｈａｍｉｓｔｙｌａ,ｓｐ．ｎ．模式标本保存在河南农业大学植物保护系昆虫标本室。     

A New Neotropical Genus and Species of Odontocerinae (Trichoptera: Odontoceridae) from Southeastern Brazil

Anastomoneura gen. nov. and A. guahybae sp. nov. are described and illustrated based on adult male and female specimens from the Mantiqueira mountain range, Minas Gerais State. This is the third genus recorded of the family Odontoceridae from South America. The new genus is characterized by the forewing anastomosis of veins R₄ and R₅ and male genitalia with a unique, tubular, projection dorsad to the plates of tergite X.     

Particle size,resource concentration,and the distribution of net-spinning caddisflies

Summary The dimensions of net meshes constructed by hydropsychid Trichoptera vary both within and between species. Despite these catchnet differences, the diets of most Hydropsychidae studied in Utah streams were statistically indistinguishable. There was no relationship between the size of available resources and catchnet construction among species assemblages inhabiting 10 different localities. A particle-size model of caddis communities, suggesting that taxa feed selectively on particle sizes corresponding to the dimension of catchnet meshes, is not supported by these data.Diatom concentration increased regularly with downstream passage in two different drainages. The identity and number of coexisting hydropsychid species and the size of their catchnets were strongly correlated with diatom concentration. Taxa with large catchnet mesh were the only residents at sites where diatom concentration was very low; as resource concentration increased downstream, species with successively smaller mesh joined the coexisting guild. Together, the broad dietary similarities and distributional pattern from Utah streams suggest that resource concentration, rather than particle size, is the basis of community organization among the hydropsychid Trichoptera.     

First report of the genus Kisaura Ross (Trichoptera, Philopotamidae) from India with the description of six new species

The genus Kisaura Ross, 1956 (Trichoptera, Philopotamidae, Philopotaminae) is reported from India the first time. Six new species are described and illustrated: Kisaura elongatasp. n., Kisaura eloctsp. n., Kisaura clavatasp. n., Kisaura gangtokensissp. n., Kisaura truncatasp. n., all from Gangtok (Sikkim) and Kisaura himachalicasp. n. from Barot (Himachal Pradesh). Male genitalia of this genus are distinguishable from those of other genera of the family by the pair of long lateral processes of tergum X, the well-developed mesoventral plates between two segments of the inferior appendages, and by the brush-like row of dark setae on the inner surfaces of the terminal segments (harpago) of the inferior appendages.     

Synonymic Notes on a Japanese Hydatophylax (Trichoptera: Limnephilidae)

Stenophylax festivus Navás, 1920 is transferred to genus Hydatophylax and Hydatophylax intermedius Schmid, 1964 is its junior synonym. Matsumura (1931) incorrectly recorded this species as Astenophylax grammicus McLachlan from Hokkaido, Japan.     

Abundance patterns of filter-feeding Caddisflies (Trichoptera : Hydropsychidae) and seston in a Montana (U.S.A.) lake outlet

The abundance patterns of four species of net-spinning caddisflies (Trichoptera : Hydropsychidae) were studied in a Montana (U.S.A.) lake outlet stream. Total Hydropsychidae reached very high densities (X > 1400 / 0.2 m²) near the lake outfall but declined precipitously downstream. Abundance patterns generally agree with a published model of filter-feeder / seston interactions in lake outlets. Larval densities were greater on moss-covered substrates and one species occupied habitats of lower water velocity compared to other species. Seston concentrations increased downstream contrary to expectation. Nutrient quality of seston may be important in predicting abundance of stream filter-feeders.     

The first parasitic Trichoptera

Abstract.

• 1 A parasitoid habit is confirmed in larvae of an Australian micro-caddisfly, Orthotrichia muscari Wells, being the first known incidence of this habit in the order Trichoptera.
• 2 Larvae of O.muscari are non-specific parasites of pupae of other caddisfly species.
• 3 O.muscari is in an Australian/New Guinean/SE Asian species group in Orthotrichia, all members of which probably share the habit. Their larvae and pupae have atypical features that are interpreted as adaptations to their uncharacteristic niche.

     

Factors affecting depth distribution of dragonflies and other benthic insects in a thermally destabilized reservoir

The distribution and abundance of macroinvertebrates along a water depth gradient were studied in thermal and ambient temperature areas of a reservoir in the southeastern United States. Benthic samples were taken at 10 depths (0.16–5 m) during January–April, 1978. Factors affecting the depth distribution of Ceratopogonidae, Chaoboridae, Chironomidae, Ephemeroptera, Odonata, and Trichoptera are discussed. The relationship between abundance of organisms and water depth was more complex than an inverse relationship generally reported in the literature.