Life Cycle of Agapetus Fuscipes (Trichoptera, Glossosomatidae) in a ﬁrst-Order Upland Stream in Central Germany Georg Beckerã

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Limnologica 35 (2005) 52–60 www.elsevier.de/limno

Life cycle of Agapetus fuscipes (Trichoptera, Glossosomatidae) in a ﬁrst-order upland stream in central Germany Georg BeckerÃ

Limnological River Station of the Max Planck Institute for Limnology, Damenweg 1, D-36110 Schlitz, Germany

Received 9 November 2004; accepted 12 January 2005

Abstract

The number of immature stages and the seasonal patterns of development are basic life history features of a stream dwelling species and knowledge about these important components are essential for understanding its adaptations to its dynamic environment. The life cycle of Agapetus fuscipes (Trichoptera, Glossosomatidae), one of the dominant scrapers in the upper and middle reaches of the Breitenbach, a first-order upland stream in central Germany, was analysed. The pronotum length and the relationship between pronotum length, larval biomass and case length showed seven distinct larval instars, contrary to earlier findings from the Breitenbach. In addition to a few trichopteran species from other functional feeding groups, A. fuscipes is the only scraping caddis fly reported to have more than five larval instars. The moult increments of pronotum length and larval biomass were distinctly lower than in glossosomatid species with five larval instars. A. fuscipes is clearly univoltine in the Breitenbach. First-instar larvae were found from July to the beginning of December, and second-instar larvae from July to January. At the beginning of December the population consisted of the instars I to V, and development did not cease during winter. The sixth-instar larvae occurred mostly in January, and the seventh-instar larvae were never present before January. The prepupae and pupae occurred in April. The last pupae were found at the beginning of September, although most of the emergence took place in June and July. At least five different immature stages with different ecological demands were present at any time throughout the year. The ecological advantage having two additional larval instars compared to other glossosomatid species may be to compensate for the high rate of mouthpart wear that occurs while the larvae feed on the rough Bunter Sandstone substratum. A further advantage may be to spread the risk of high mortality under unfavourable environmental conditions. r 2005 Elsevier GmbH. All rights reserved.

Keywords: Agapetus fuscipes; Life cycle; Seven larval instars; Larval biomass; Case length; Moult increments; Breitenbach; Upland stream

Introduction as the functions and interactions of biological commu- nities (e.g. Butler, 1984; Roff, 1992; Stearns, 1992). Basic information on a species’ life history is essential Knowledge of the number of immature stages and the for understanding its adaptation to its environment as well patterns of growth and development throughout the year is an important component of this basic information. ÃTel.: +49 6642 960 360; fax: +49 6642 6724. Glossosomatid larvae are typical scrapers in rivers E-mail address: [email protected] (G. Becker). and streams of all faunal regions (Wiggins, 1996).

Glossosomatid species generally have five larval instars The objective of the current study was to answer the (e.g. Anderson & Bourne, 1974; Irons, 1988; Sameshima following questions: (i) How many distinct larval stages & Sato, 1994; Houghton & Stewart, 1998), which is also exist in the Breitenbach? (ii) Can these larval stages be typical for most other Trichoptera. However, Agapetus distinguished on the basis of pronotum length, larval fuscipes Curtis is an exception. Several authors have biomass, and case length? (iii) Are the moult increments reported more than five larval instars (Nielsen, 1942; of pronotum length, larval biomass, and case length Benedetto, 1975; Iversen, 1976; Recasens & Murillo, between the larval instars smaller than in trichopteran 1986; Sangpradub, Giller, & O’Connor, 1999). A. species with five larval instars? (iv) What are the fuscipes is common in European upland and lowland durations of the individual larval stages present in the streams (Botosaneanu & Malicky, 1978; Pitsch, 1993; Breitenbach throughout the year? Robert, 2001; Fischer, 2003; Nijboer, 2004) and is one of the dominant trichopteran species in the upper and middle reaches of the Breitenbach, a first-order upland stream in central Germany (Illies, 1978, 1983; Sandrock, Methods 1978; Wagner & Schmidt, 2004). The larvae scrape on the stony substrata of the Breitenbach (Becker, 1990, The permanent flowing stretch of the Breitenbach is 1994) and have a significant influence on the structure some 2 km in length and rarely exceeds 1 m in width. and species composition of epilithic biofilms (G. Becker, The stream is fed by several springs and flows through a unpublished data). grassland valley, mostly unshaded by trees, before However, the existing data on this species are entering the River Fulda. The dominant geology in the insufficient and partly contradictory (Table 1). Nielsen area is Bunter Sandstone. (1942), Iversen (1976), Recasens & Murillo (1986), and The larvae of A. fuscipes, used to analyse pronotum Sangpradub etal. (1999) reported seven larval instars in length, body mass and case length, were sampled differentEuropean streams, while Benedetto (1975) between January 1999 and December 2002 in the upper, reported eight larval instars in laboratory studies, but perennial reach of the Breitenbach, which has an annual could not find all of these instars in the Breitenbach. mean temperature of about 8 1C and an annual Frequency histograms of the pronotum length, which temperature amplitude of between 4 and 16 1C (H. H. enable the individual instars of A. fuscipes tobe Schmidt, unpublished data). All analyses were under- distinguished, and also data on the mean biomass of taken with fresh larvae and cases. After anesthetization individual larval stages have not been published. with CO2, pronotum length was measured along the Benedetto (1975) analysed only the biomass of freshly mid-dorsal ecdysial line using a dissection microscope hatched larvae. However, the specific information about (magnification 100 ). Additionally, the length of the instar number and size are essential for understanding corresponding larval case was measured. Pronotum the seasonal timing of various life cycle processes, length was the preferred measurement because preli- population synchrony, distributional pattern, and the minary investigations had shown that the differences persistence in the face of disturbance. Size (biomass) is between the larval instars were more distinct than when especially important with respect to risk factors such as tarsus length or the more commonly head capsule width predation and exposure to hydrodynamic forces. were used. Young larvae and their cases (instars I–III)

Table 1. Comparison of literature data on the life history of A. fuscipes

Authors Life history Larval Larval Larval Prepupal Larval Larval Case Country instars head pronotum pronotum biomass length length capsule length length width

Nielsen (1942) 7 x x x Denmark

Benedetto (1975) Univoltine 8 x x x Germany

Recasens & Murillo Bivoltine 7 x x Spain (1986)

Sangpradub etal. (1999) Univoltine 7 x Ireland

Becker (present study) Univoltine 7 x x x x Germany ARTICLE IN PRESS 54 G. Becker / Limnologica 35 (2005) 52–60 were weighed in groups of up to 15 individuals because distinctly separated (Fig. 1a). The pronotum lengths of of their low body mass and the averaged values were instars I to V were distinct, whereas the peaks of instars used for further calculations. The older larvae (instars VI and VII overlapped slightly. The frequency diagram IV–VII) and their corresponding cases were analysed of the pronotum lengths of larvae (instars I–III) individually. Larvae and cases were frozen at 20 1C, that had hatched and grown in the laboratory culture and dried at105 1C for 24 h before they were weighed (Fig. 1b) corresponded exactly with the field specimens, and reweighed after ashing at 510 1C for 8 h. demonstrating that all the existing larval instars of Glossosomatid larvae build a new case after each A. fuscipes were presentin thefield samples. The range moult and the larval case cannot be altered within an of the pronotum lengths of instar-VII larvae corre- instar (Hansell, 1968; Anderson & Bourne, 1974; Bohle sponded well with the prepupal pronotum lengths & Fischer, 1983). Thus larvae with light-coloured (Fig. 1c). The prepupae had reached the end of the sclerites, which had moulted shortly before, were larval development, and were enclosed in their pupal excluded from the calculations of the relationships cases shortly before pupation. Thus the last two peaks between pronotum length, larval biomass, and case indicated two different larval instars rather than sexual length. This approach was taken because the larvae dimorphism in the last larval instar. moultin theirold case before building a new case, and it The case lengths, and especially the larval biomasses, is the new case that characterizes the new larval instar. of the instars partly overlapped (Table 2 and Fig. 2). To ensure that the youngest larval stage was not missed However, the pairwise comparison of case length and in the field, egg masses were sampled from the upper biomass showed significant differences between the reach of the Breitenbach in August (see also Becker, seven larval instars (Mann-Whitney U-test, all pairs 1991) and cultured in laboratory streams at about 14 1C. with both parameters po0.001). When the pronotum After hatching, young larvae were fed for 6 weeks with length was used to distinguish the larval instars, the epilithic biofilms from the Breitenbach, with the biofilms correlation between pronotum length, larval biomass, being replenished once a week. Larvae from this culture and case length (Fig. 3) showed clear distinction were sampled and measured regularly throughout this between the four older larval instars (IV–VII). The period. The pronotum lengths of the young larvae values of instar-VII larvae are widely distributed (instars I–III) from the laboratory streams were then compared to the other instars because approximately compared with larvae from the field samples. Because 55% of the mean larval biomass of the instar-VII larvae distinction between sexes in the last larval instar of was accumulated during the development of this larval Trichoptera is not reliable, ranges of prepupal pronotum stage (see also Table 2 and Fig. 4). lengths from the upper reach of the Breitenbach were Throughout the ontogeny, the ranges of all three used to avoid counting the smaller males and the larger parameters increased with each successive larval stage females as two different instars. (Table 2). The mean moultincrementof pronotum Qualitative samples were taken on 40 occasions lengths throughout the ontogeny was 1.35, and the value between February 1997 and November 2003 in the decreased from 1.67 at the second-instar/first-instar upper reach of the stream within the context of various moult to 1.20 at the seventh-instar/sixth-instar moult. investigations. These data provided information on The regression between pronotum length and larval the occurrence of the different developmental stages of instar showed a linear function (Fig. 4). The mean moult A. fuscipes in the Breitenbach. increment of the larval AFDM was 2.25, and the value Statistical analyses were conducted using the software decreased from 2.64 at the second-instar/first-instar package SPSS 11.5 (SPSS Inc.) Differences between the moult to 2.28 at the seventh-instar/sixth-instar moult. measurements of the various larval instars were com- The regression between larval AFDM and larval instar pared using sequential Mann-Whitney U-tests. P-values showed a typical exponential growth curve (Fig. 4). The were considered significant after adjustment with the mean moultincrementof case lengthswas 1.26 and was Bonferroni method (Sokal & Rohlf, 1995). Thus, in the relatively constant throughout the ontogeny. The pairwise comparison of seven instars, six tests were regression between case length and larval instar showed conducted and p-valueso0.0083 were considered sig- a slightly exponential function (Fig. 4), buta linear nificant. The regression analyses were conducted using regression also had a high correlation coefficient (0.95). the software package SigmaPlot 7.0 (SPSS Inc.). An analysis of the population structure of A. fuscipes throughout the year showed a clearly univoltine life cycle in the upper reach of the Breitenbach (Fig. 5). The composite of the data material of 6.5 years of collection Results showed little variance between the years (Fig. 5, thin lines). Instar-I larvae occurred in mid-July and were The frequency histogram of the pronotum lengths found until the beginning of December. Instar-II larvae shows seven larval stages of A. fuscipes that were were found from mid-July until January, instar-III and ARTICLE IN PRESS G. Becker / Limnologica 35 (2005) 52–60 55

Fig. 1. Frequency distributions of the pronotum length of the seven larval instars of A. fuscipes (A) in the Breitenbach (n ¼ 1056) and (B) in laboratory culture (n ¼ 50). (C) Frequency distributions of the pronotum length of prepupae from the Breitenbach (n ¼ 86). Explanations: I–VII ¼ larval instars; PP ¼ prepupae.

instar-IV larvae from mid-August until mid-March and the season, in September. Sixth-instar larvae were found end of April, respectively. Instar-V larvae were found until the end of June. Instar-VII larvae never occurred from the beginning of September, rarely from the end of before January, and the last individuals were recorded at August, until mid-June. At the beginning of December the end of August. The ﬁrst prepupae developed in mid- the population consisted of the instars I to V. Detailed April and were present until mid-August. Pupae observations showed that these larvae were feeding occurred at the end of April and were found until the intensively throughout the winter, and that their beginning of September. However, most of the popula- development was not interrupted. Sixth-instar larvae tion pupated between May and July. At least ﬁve were generally notfound before January. Only in one different developmental stages of A. fuscipes coexisted in year were some instar-VI larvae found much earlier in the Breitenbach at any given time of the year (Fig. 5). ARTICLE IN PRESS 56 G. Becker / Limnologica 35 (2005) 52–60

Table 2. Pronotum length (mm) of larval instars and prepupa, and larval biomass (mg) and case length (mm) of larval instars for A. fuscipes in the Breitenbach

Instar Mean SD Range Min. Max. N Moult increment

Pronotum length (mm) I 99 8.2 40 80 120 86 II 165 9.5 40 140 180 57 1.67 III 221 13.2 50 200 250 94 1.34 IV 297 18.9 70 260 330 210 1.34 V 386 19.2 80 350 430 185 1.30 VI 475 20.4 80 440 520 175 1.23 VII 569 29.0 110 520 630 251 1.20 PP 573 27.6 110 520 630 86 AFDM (mg) I 3.3 1.5 4.2 1.6 5.8 6 (85) II 8.6 2.9 7.9 4.7 12.5 5 (57) 2.64 III 22.8 6.4 22.0 14.0 36.0 5 (45) 2.65 IV 37.0 11.9 44.0 17.0 61.0 31 1.62 V 80.4 28.3 126.0 32.0 158.0 45 2.17 VI 171.2 44.1 182.0 89.0 271.0 59 2.13 VII 390.7 184.4 956.0 142.0 1098.0 85 2.28 Case length (mm) I 1.55 0.17 0.96 1.22 2.18 86 II 1.94 0.23 1.25 1.43 2.68 57 1.25 III 2.54 0.26 1.17 1.78 2.95 44 1.31 IV 2.91 0.29 1.10 2.47 3.57 33 1.15 V 3.68 0.34 1.25 3.19 4.45 45 1.26 VI 4.96 0.29 1.49 3.91 5.40 59 1.35 VII 6.04 0.61 2.85 4.75 7.60 85 1.22

The moult increments for pronotum length, biomass and case length between the larval instars are shown. I –VII ¼ larval instars, PP ¼ prepupae.

of Europe (Nielsen, 1942; Iversen, 1976; Recasens & Murillo, 1986; Sangpradub etal., 1999 ). Because of the continuous increase of the larval biomass throughout the ontogeny, distinguishing the larval instars based on biomass is notpossible. The clear distinctionof the larval instars in A. fuscipes using the correlation of pronotum length, larval biomass, and case length (Fig. 3) may be possible because of the step-like increase not only of the pronotum length, but also of the case length, after each moult. In contrast to many other trichopteran larvae, glossosomatid larvae do not length- en and widen their case continuously as they grow. Glossosomatid larvae build a new case after each moult and do not alter the size of the case within an intermoult period (Hansell, 1968; Anderson & Bourne, 1974; Bohle Fig. 2. Relationships between pronotum length (mm) and case & Fischer, 1983). length (mm) for the three youngest larval instars of A. fuscipes. Although glossosomatid larvae are common and Explanations: I–III ¼ larval instars. often abundant (Wiggins, 1996), the life cycle and number of larval instars are only documented in a few species. Of the 14 glossomatid species in Central Europe Discussion (Pitsch, 1993), the number of instars is known in only three species besides A. fuscipes: Synagapetus iridipennis In the Breitenbach, A. fuscipes clearly has a univoltine (Otter, 1989), Glossosoma conformis (Sangpradub etal., life history and seven distinct larval instars. These 1999), G. intermedia (Fjellheim & Raddum, 1998). These observations concur with the ﬁndings of several authors, three species each have ﬁve larval instars, as do Agapetus who have described seven larval instars in various parts yasensis and G. inops in Japan (Sameshima & Sato, ARTICLE IN PRESS G. Becker / Limnologica 35 (2005) 52–60 57

Fig. 5. Life cycle of A. fuscipes in the upper reach of the Breitenbach. Explanations: I–VII ¼ larval instars; PP ¼ pre- Fig. 3. Relationship between pronotum length (mm), larval pupae; P ¼ pupae; A ¼ adults [emergence data from Illies biomass (mg), and case length (mm) in older larval instars of (1971, 1978), Sandrock (1978), Fischer etal. (1998) , Wagner & A. fuscipes. Explanations: IV–VII ¼ larval instars. Schmidt(2004) ]. Bold lines ¼ larvae were found regularly; ﬁne lines ¼ larvae were found seldom.

major life cycle features such as development and growth patterns underlie a strong lineage-specific con- trol and may be fixed within lineages (e.g. Butler, 1984; Stearns, 1992). The number of seven larval instars within A. fuscipes seems to be fixed, because only Benedetto (1975) found eightlarval instarsin laboratoryculturesof larvae from the Breitenbach, but not in the Breitenbach itself. However, the data he reported for pronotum lengths are difficult to interpret. He noted a mean pronotum length of 200 mm for first-instar larvae, and up to 1550 mm for lastinstar( Table 3). The currentstudyhas shown that larvae with a mean pronotum length of 200 mm belong to the third instar, and that larvae with a Fig. 4. Regression lines and functions of moult increments of pronotum length, larval biomass, and case length in larval pronotum length of more than 630 mm were notfound in instars. the Breitenbach. On the other hand, Benedetto (1975) measured head capsule widths in last instar larvae that were distinctly less than the widths reported by 1994), and A. pontona and A. monticolus in Australia Sangpradub etal. (1999) for larvae of A. fuscipes in an (Marchant& Hehir, 1999 ). Eighty glossosomatid species Irish stream. Thus the findings of Benedetto (1975) do are known in the Nearctic region (Wiggins, 1996). not concur with measurements reported by other However, the life cycle of only nine of these species has authors for larvae in the Breitenbach and other streams. been analysed (overview in Houghton & Stewart, 1998). Few Trichoptera species in the northern hemisphere Two of these nine species are Agapetus species: A. bifidus are known to have more than five larval instars. Iversen (Anderson & Bourne, 1974) and A. illini (Bowles & (1976) reported six larval instars in the headwater Allen, 1992). All nine species were found to have five species Berea maurus, with a non-synchronous life larval instars. Thus A. fuscipes is the only scraping history, in a Danish spring. In some Sericostama species caddisfly species in the Northern Hemisphere currently the number of larval stages is not clear, and it is not known to have more than five larval instars. That means known whether the number of stages is fixed or variable. that one important life cycle feature of this species, the In Sericostoma personatum, differentnumbers of larval instar number, differs markedly from the typical number instars have been described: five by Nielsen (1942), six of larval instars in Trichoptera and all the other by Elliott (1969), and seven by Iversen (1973) and glossosomatid species that have been analysed in detail Wagner (1990). Resh etal. (1981) observed that the to date. This finding is of particular importance because larvae of Gumaga nigricula (Sericostomatidae) moulted ARTICLE IN PRESS 58 G. Becker / Limnologica 35 (2005) 52–60

Table 3. Comparison of studies reporting pronotum measurements of larval instars of A. fuscipes. Only studies that included mean and variance, or range, of the pronotum lengths for all larval instars are included

Larval instar

Authors I II III IV V VI VII VIII Prepupa

Benedetto (1975) Mean (N) 200 250 400 500 650 750 1050 1250/1550 N 252 380 1652 3507 3581 1070 1245 1007 Recasens & Murillo (1986) Range 70–112 126–168 182–238 239–294 295–364 365–420 421–574 Becker (presentstudy) Mean ( 7SD) 9978.2 16579.5 221713.2 297718.9 386719.2 475720.4 569729.0 573727.6 Range (N) 80-120 140-180 200–250 260–330 350–430 440–520 520–630 520–630 N 86 57 94 210 185 175 251 86

14 times, and Denis (1981) assumed 10 larval stages in 1942). In four Japanese glossosomatid species with five Sericostoma galeatum. These are detritivore species, larval instars, the mean moult increments for head mostof which have a semivoltine,or longer life cycle. capsule lengths ranged between 1.41 and 1.49 (calcu- Further, in some trichopteran species with a non- lated from Sameshima & Sato, 1994). The average of synchronous life history from the southern hemisphere, 1.35, and the minimum of 1.2, for the moult increment higher numbers of larval instars than the typical five for the pronotum length of the seven larval stages in have been assumed (Winterbourn, 1978; Towns, 1981; A. fuscipes were distinctly lower (Table 2). The moult Dean & Cartwright, 1987). increments of the larval biomass in A. fuscipes showed a The pronotum lengths of the different larval instars in typical exponential function and the mean moult this study concur with the results of Recasens & Murillo increment of 2.25 was distinctly lower than the values (1986). These authors reported pronotum lengths for of 2.79 and 2.92 in two Australian Agapetus species with A. fuscipes in a Spanish stream (Catalonia, SE Spain) five larval instars (calculated from Marchant& Hehir that were somewhat smaller than in the Breitenbach 1999). The relationship between moult increments of population (Table 3). However, they noted that case length and larval instars was slightly exponential. A. fuscipes had a bivoltine life history, and the shorter The duration of a life cycle can be highly variable in generation time may explain the smaller size of their the Glossosomatidae, ranging from 1.5 months for the larvae. Nielsen (1942) found that case lengths of the first summer generation of the trivoltine population of larval instars of A. fuscipes in a Danish stream ranged G. inops at water temperatures between 17.5 and 20 1C between 1.33 and 1.85 mm, and that case lengths of the (Sameshima & Sato, 1994) to nearly one year for most last larval instars ranged between 4.6 and 8.0 mm, both species in the northern hemisphere at lower tempera- of which concurred with the case lengths reported in the tures (e.g. Fjellheim & Raddum, 1998; Sangpradub et currentstudyfor A. fuscipes in the Breitenbach al., 1999). A. fuscipes in the upper reach of the (1.22–2.18 mm and 4.75–7.6 mm, respectively). Breitenbach showed a clearly seasonal life cycle with The larval biomass of A. fuscipes is relatively low distinct annual classes and slowly growing larvae. The compared to the case mass (Becker, 2001). The AFDM composite of 40 qualitative samples over 6.5 years values of the last instar larvae in the current study were showed little differences of the population structure of relatively low (mean7SD, 391784 mg). No comparable A. fuscipes between the years (Fig. 5) due to the relative data for the AFDM of glossosomatid larvae could be constant water temperature (average 8 1C) atthe found in the literature. Benedetto (1975) analysed only sampling site nearby the main spring (H. H. Schmidt, the dry mass of freshly moulted A. fuscipes, and notthe pers. comm.). However, the population was relatively mean dry mass of individual larval instars. Fjellheim & asynchronous. Thus individuals in several size classes Raddum (1998) and Marchant& Hehir (1999) calcu- occurred at all times of the year. Most of the larval lated the mean dry mass of preserved larvae, and biomass was accumulated in late winter and spring. reported values ranging between 200 and 300 mg for last These characteristics correspond well with the slow instar larvae of three different glossosomatid species, seasonal life cycle in the classification scheme of Hynes which were lower than the findings of the current study (1970). The emergence period in the Breitenbach ranges for larvae of A. fuscipes in the Breitenbach. from May to September (Illies, 1971; Sandrock, 1978; The moult increment for hard cuticle parts between Fischer, Fischer, Schnabel, Wagner, & Bohle, 1998; two larval stages (Dyar’s rule) of trichopteran species Wagner & Schmidt, 2004). However, mostadults(88%) with five larval instars amounts to about 1.5 (Nielsen, emerged in June and July (Sandrock, 1978). First-instar ARTICLE IN PRESS G. Becker / Limnologica 35 (2005) 52–60 59 larvae were presentfor nearly 4.5 months, from mid- References July to the beginning of December, and instar-II larvae were present for 6 months, from mid-July to mid- Anderson, N. H., & Bourne, J. B. (1974). Bionomics of three January, due to the extended emergence period. species of glossosomatid caddis flies (Trichoptera: Glosso- Individuals of at least five immature stages were present somatidae) in Oregon. Canadian Journal of Zoology, 52, throughout the year. These characteristics of the 405–411. immature stages do not agree well within Hynes (1970) Arens, W. (1990). Wear and tear of mouthparts: a critical slow seasonal life cycle classification. problem in stream animals feeding on epilithic algae. Canadian Journal of Zoology, 68, 1896–1914. Because the number of glossosomatid species with Becker, G. (1990). Comparison of the dietary composition of well known life histories and larval stages is relatively epilithic trichopteran species in a first-order stream. Archiv small, it is not known whether a life cycle with more fu¨r Hydrobiologie, 120, 13–40. than five larval instars is within the normal phylogenetic Becker, G. (1991). Ovipositing behaviour of Agapetus fuscipes variability of Glossosomatidae, or whether the large (Trichoptera: Glossosomatidae) in a small Central Eur- number of larval instars is a species-specific adaptive opean upland stream. In C. Tomaszewski (Ed.), Proceed- strategy of A. fuscipes to headwater streams like the ings of the 6th International Symposium on Trichoptera, Breitenbach, which would indicate an adaptive response Lodz and Zakopane, Poland, 1989 (pp. 143–147). Poznan: to long-term environmental effects (e.g. Butler, 1984; Adam Mickiewicz University Press. Sweeney, 1984). The life history traits of A. fuscipes are Becker, G. (1994). Food preference by five trichopteran more complex than the typical lineage-specific con- scrapers. Hydrobiologia, 273, 171–178. straints in Trichoptera. Thus it is relevant to question Becker, G. (2001). Larval size, case construction and crawling the ecological advantage of this atypical number of velocity at different substratum roughness in three scraping caddis larvae. Archiv fu¨r Hydrobiologie, 151, 317–334. immature stages to A. fuscipes. Two findings seem to be Benedetto, L. (1975). O¨ kologie und Produktionsbiologie von important in this context. On the one hand, the larvae Agapetus fuscipes Curt. im Breitenbach 1971–1972. Archiv specifically feed on very thin biofilms in the Breitenbach, fu¨r Hydrobiologie, Suppl, 45, 305–375. even on biofilms with low chlorophyll-a content of as Bohle, H. W., & Fischer, M. (1983). Struktur und Entstehung 2 little as 0.2 mgcm (G. Becker, unpublished data). The der Larven-und Puppengeha¨ use einiger Glossosomatidae high abrasion of the mouthparts due to feeding off the und Rhyacophilidae, insbesondere bei Synagapetus iridi- rough surface of Bunter Sandstone substratum (Arens, pennis (Trichoptera: Rhyacophiloidea). Entomologia Gene- 1990) may be compensated for by two extra moults. On ralis, 9, 17–34. the other hand, the wide range of larval size classes Botosaneanu, L., & Malicky, H. (1978). Trichoptera. In J. present at the same time, which is extended by having Illies (Ed.), Limnofauna Europea (pp. 333–359). Stuttgart. two additional larval instars, may enhance the ability of Bowles, D. E., & Allen, R. T. (1992). Life histories of six A. fuscipes to cope with unfavourable conditions in their species of caddisflies (Trichoptera) in an Ozark stream, abiotic and biotic environment, spreading the risk of USA. Journal of the Kansas Entomological Society, 65, high mortality (Den Boer, 1968; Danks, 1987). Atleast 174–184. Butler, M. G. (1984). Life histories of aquatic insects. In V. H. five different immature stages, each with different Resh, & D. M. Rosenberg (Eds.), The ecology of aquatic ecological demands (Majecki, Schot, Verdonschot, & insects (pp. 24–55). New York. Higler, 1997; Nijboer, 2004), for instance with respect to Danks, H. V. (1987). Insect dormancy: An ecological perspec- risk factors such as predation and exposure to hydro- tive. Biological Survey of Canada, Monograph Series 1, dynamic forces and nutritional requirements, were National Museum of Natural Sciences, Ottawa. present throughout the year. Between five and eight Dean, J. C., & Cartwright, D. I. (1987). Trichoptera of a developmental stages are present at the same time, inside Victorian forest stream: species composition and life and outside the stream, if the egg and adult stages are histories. Australian Journal of Marine and Freshwater included. Further studies are needed to understand how Research, 38, 845–860. 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