spatial and temporal distribution of caddisfly larvae in two lowland streams in the netherlands (trichoptera) Rob Franken, Bert Klutman & David Tempelman Caddisflies are a species rich insect order. The adults are moth-like, but their wings bear hairs instead of scales. The larvae are aquatic and live in self-constructed cases, made of plant material, sand or debris. The species are used as indicators of water quality, but much is still not known about their biology and ecology. In this paper the preferred substrates and phenology of the larvae of 13 species are described, using the data of a survey of two lowland streams in the east of the Netherlands. caddisfly species distributions in streams, along introduction with temperature, current velocity, food (size) and Streams are heterogeneous environments, both dissolved oxygen. spatially and temporally. The spatial distribution of aquatic invertebrates is in part determined by Temperature affects the development, and at habitat conditions, such as substrate composition, temperate latitudes most caddisflies complete a oxygen availability and current velocity. Temporal single generation in the course of one year. Food variation in species abundance is to a large extent resources probably affect the number of cohorts, caused by seasonal changes in the physical and and seasonal differences in growth periods may chemical environment (e.g. temperature, discharge expose coexisting species to different food re- and the availability of food resources). sources, whereas differences in flight period may result from seasonal growth periods or diapause So far, not much is known about the preferences (Mackay & Wiggins 1979, Wiggins 2004). of caddisfly larvae for substrates within the aquatic habitats or the periods of the year when larvae can be found. There is a need for more information on species distributions in general (Higler 2008b). Caddisflies (Trichoptera) are holometabolous insects (fig. 1-3) with an aquatic larval stage (fig. 4-6). The larvae secrete silk to construct a diverse array of portable cases, fixed shelters, filter nets and cocoons (Wiggins 2004). The cases are constructed from mineral grains and vegetation fragments and have different func- tions, such as to meet respiratory needs (Williams et al. 1987), providing protection from predators (Otto & Johansson 1995) and resisting flow induced dislodgement (Waringer 1993). As all Figure 1. Anabolia nervosa, larva in case (Woudhuizer- species need a case in order to reach the pupal mark, The Netherlands). Photo David Tempelman. stadium (Mackay & Wiggins 1979), substrate Figuur 1. Anabolia nervosa, larve in koker (Woud- composition is one of the major factors in huizermark). Photo David Tempelman. franken et al. ‒ spatial and temporal distribution of caddisfly larvae 81 NFM42 (13) 081-094 Franken et al.indd 81 12-06-14 10:58 Figure 2. Anabolia nervosa, adult in the field (Smalwater, The Netherlands). Photo David Tempelman. Figuur 2. Anabolia nervosa, adult in het veld (Smalwater). Foto David Tempelman. Figure 3. Hydropsyche angustipennis, larva (Anserbeek, The Netherlands). Photo David Tempelman. Figuur 3. Hydropsyche angustipennis, larve (Anserbeek). Foto David Tempelman. Figure 4. Hydropsyche angustipennis, adult resting on a leaf along a stream (Kleine Aa, Noord-Brabant, The Nether- lands). Photo David Tempelman. Figuur 4. Hydropsyche angustipennis, adult rustend op een blad langs een beek (Kleine Aa, Noord-Brabant). Foto David Tempelman. Figure 5. Limnephilus lunatus, larva in case (sand pit, Hoogeveen, The Netherlands). Photo David Tempelman. Figuur 5. Limnephilus lunatus, larve in koker (zandwinplas Hoogeveen). Foto David Tempel- man. 82 e 42 ‒ 2014 NFM42 (13) 081-094 Franken et al.indd 82 12-06-14 10:58 Figure 6. Limnephilus lunatus, adult in the field (Berkheide, The Netherlands). Photo Casper Zuyderduyn. Figuur 6. Limnephilus lunatus, adult in het veld (Berkheide). Foto Casper Zuyderduyn In the Netherlands, most caddisfly species inhabit streams. Most information on larval distributions is based on routine sampling (often a single composite sample, once a year) by Water Boards (Higler 2005, 2008a). The results which are pre- sented here are part of a study in which the spatial and temporal variation in invertebrate communi- ties in two streams (Boven Slinge, Bekendelle and the Ramsbeek) were quantified at the scale of the mesohabitat, with intensive sampling (Franken & Klutman, in prep.). Mesohabitats are distinct patches of contrasting structure which describe the variability in a stream (Maddock 1999). Addition- ally, ecological, distributional and phenologic notes are included for each species. These are based on Higler (2008a), personal observations by the third author and waarneming.nl. The aim of this paper is to present new information on the ecology of a number of caddisfly species. Figure 7. Location of the sampling sites. Figuur 7. Locatie van de monsterpunten. materials and methods The sampling site (fig. 7) at the Boven Slinge (51.942º, 6.694º) is situated in nature reserve of this paper called fine detritus), banks, pool Bekendelle, which is one of the few swamp forests (deep with low current), riffle (shallow with fast in the Netherlands. The sampled section of this current) and dead wood. The sampled section of lowland stream meanders freely and is character- the Ramsbeek (52.087º, 6.692º) has been restored ised by pulsed discharges as a result of the imper- in 2010. The stream has been placed back to its meable clay layers of the surrounding area. The old course, the bed level was raised and small highest peak discharge during this study was 6.17 meanders were created. It is a half-open channel, m3/s (12-month average = 0.65 ± 0.93 (sd) m3/s with only trees at the west side, and high banks. (continued measurements, approximately 800 me- Sampled mesohabitats were sand, vegetation and ters upstream). Sampled mesohabitats (described fine detritus. In-stream vegetation cover was high by the major substrate type) were sand, vegetation, (30-40 %) at the Ramsbeek in summer, whereas at fine particulate organic matter (fpom, in the rest the Boven Slinge it was less than 5 %. franken et al. ‒ spatial and temporal distribution of caddisfly larvae 83 NFM42 (13) 081-094 Franken et al.indd 83 12-06-14 10:58 All mesohabitats were sampled monthly for Table 1. Caddisfly species caught and the number per 12 months from September 2012 until August stream. 2013 in both streams, except for banks and Tabel 1. Gevangen kokerjuffersoorten met het aantal vegetation in September 2012 at the Boven Slinge. per beek. Invertebrates were sampled by sweeping a D-frame hand-net (500 µm mesh, 30 × 20 cm). Species Boven Rams- In every sample, the length from which a sample Slinge beek was taken was recorded. Due to the nature of Anabolia nervosa 1335 79 the sampled habitat, which varies a lot over the Athripsodes aterrimus - 10 stretches which where sampled, they should be Athripsodes cinereus 52 - considered semi-quantitative. Dead wood and Beraeodes minutus 1 - aquatic vegetation, however, were hand-picked. Cyrnus trimaculatus 36 - For comparison among mesohabitats, they were Glyphotaelius pellucidus 97 - expressed as a sweep sample. Samples were Halesus radiatus 142 7 sorted at the same day and preserved in 80 % Hydropsyche angustipennis 637 19 ethanol. Hydropsyche pellucidula 28 - Hydroptila 1 3 Ironoquia dubia 11 15 description of mesohabitats Limnephilus extricatus - 4 Mesohabitat sand consisted of bare sand with Limnephilus flavicornis 3 1 some organic debris only. Dead wood was made Limnephilus lunatus 82 182 up of woody litter like large branches and tree Limnephilus rhombicus 85 2 trunks which were collected from the stream bed. Lype reducta 251 - Fine detritus on sand, was mainly collected at the Molanna angustata 2 24 shallow edges. Riffle substrates consisted of coarse Mystacides azurea 12 - sand and fine gravel, along with coarse organic Mystacides longicornis 7 1 matter and twigs, whereas pool substrates Mystacides niger 20 43 consisted of sand covered by a layer of particulate Oecetis ochracea - 1 organic matter. The aquatic vegetation of the Phryganea bipunctata 1 2 Boven Slinge is dominated by Sparganium Phryganea grandis - 1 emersum and some Agrostis stolonifera. The Rams- Potamophylax rotundipennis 249 2 beek is dominated by Callitriche obtusangula and Tinodes waeneri 7 - some Lemna minor and Elodea nuttallii. results individuals was > 50. Vegetation and banks might In total 22 caddisfly species were collected at the be underestimated as macroinvertebrates were not Boven Slinge and 18 at the Ramsbeek (table 1). sampled in September 2012. However, most The caddisfly larvae made up 11 % (Boven species had a low abundance in autumn or in Slinge) and 4 % (Ramsbeek) of the number these mesohabitats, except for Potamophylax of individuals caught. Pie charts with the rotundipennis in banks and Hydropsyche distribution over the mesohabitats were only angustipennis in vegetation and Limnephilus generated for species of which more than 20 indi- rhombicus in both banks and vegetation. viduals were collected throughout the study, in a For some species a distinction was made between single stream. Temporal variation in species early and later instars, as apparent differences in abundance is only shown when then number of spatial distribution were observed. 84 e 42 ‒ 2014 NFM42 (13) 081-094 Franken et al.indd 84 12-06-14 10:58 Anabolia nervosa adult mainly in summer (May-September). The species can be observed flying in groups just In both streams (fig. 8, 9) larvae of A. nervosa before sunset, in an up and down courtship Curtis, 1834 (fig.1, family Limnephilidae) were display. It is attracted to at light; most individuals most abundant in fine detritus (46 and 73 %, are found just after dusk. respectively), and also in the pool at Boven Slinge (21 %, fig. 8). Cases were stronger (larger pieces of woody debris) in the riffle, when compared to Cyrnus trimaculatus those in fine detritus and the pool (pers. obs. Rob Franken), which is probably a result of the sorting Larvae of C.