Life History of a Net-Spinning Caddisfly, Parapsyche Shikotsuensis in a Headwater Stream of Hokkaido, Northern Japan Tomiko

Jpn. J. Limnol., 60 : 159-175, 1999

Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis in a Headwater Stream of Hokkaido, Northern Japan

Tomiko ITO

ABSTRACT The life history of a net-spinning caddisfly, Parapsyche shikotsuensis was studied in a headwater stream, a tributary of Ichankoppe Creek, Eniwa, Hokkaido, northern Japan, 1994-1996. This species is univoltine with an early and mid-summer adult period. Females deposit eggs either above- or underwater on cobbles and wood debris. Early instar larvae appear in August, and almost all of them develop to fifth instar by December. Larvae grow and develop even in winter. Larvae live on riffles, wood debris and the submerged leaves and stems of living riparian plants. Second, third and fifth instar larvae were found at a relatively high density in riffles. Gut contents of larvae are mostly composed of animal fragments (55-95%) and vascular plant fragments (5-45%). The animal-fragment frequency in the guts was relatively low in fourth instar larvae and in October. Moreover, a comparison among the same instar larvae collected in different months showed that animal-fragment frequency was low in October for third, fourth and fifth instar larvae.

Key words : gut contents, life cycle, oviposition, Parapsyche

INTRODUCTION The caddisfly of the genus Parapsyche is a net-spinner and one of the major components of aquatic insects communities in East Asian and North American mountain streams (WIGGINS, 1996). Life cycle, food, habitat and production have been studied for several North American species (MALAS and WALLACE, 1977; BENKE and WALLACE, 1980; HAEFNERand WALLACE, 1981 ; DUDLEY and ANDERSON, 1982 ; SINGH et al., 1984 ; HURYN and WALLACE, 1988 ; DUDGEONand RICHARDSON,1988). However, its ecology is poorly known in Asia except for the gut contents of P. maculata (ULMER) (TANIDA, 1982) and the ovipositional behavior of P. shikotsuensis (IWATA) and P. aureocephala SCHMID (KURANISHI, 1992). The author will report on the life cycle, adult period, sex ratio, female maturation, oviposition site, substratum preference of larvae, and gut contents in larvae of P. shikotsuensis in a headwater stream of Hokkaido, northern Japan. 160 ITO

STUDY SITE AND METHODS

Study site The life history of P. shikotsuensis was studied in a second-order stream

(based on the 1 : 20,000 topographic map of the Hokkaido Forest Office), a tributary of Ichankoppe Creek, the Izari River, Eniwa, Hokkaido, northern

Japan (42•‹49' N, 141•‹29' E). The stream, 1.5-2.5 m wide at the study site,

drains a watershed of 1.6 km2. The terrestrial vegetation consists of decidu-

ous trees (mainly Acer mono MAXIM., Alnus hirstuta TURCZ., Tilia japonica SIMONKAI, Salix spp., Ulmus spp.) and coniferous trees (mainly Abies

sachalinensis MASTERS). The whole drainage basin is well canopied.

Water temperature at 12:00-14:00, pH, electric conductivity and dis- charge, which were measured at the collecting dates of immature stages , ranged from 4.2-11.4•Ž, 7.0-7.1, 40-72 cm S-1 and 0.024-0.078 m3 S-1 , respectively (Table 1). Turbellaria, Ephemeroptera (Paraleptophlebia spp., Ephemerellidae, Baetidae), Plecoptera (Nemouridae) and Chironomidae

were abundant (Table 1). Further biological conditions of the site were

reported by ITO (1996).

Table 1. Physical, chemical and biological condition of the study site and substrata collected. Average and range (in parentheses) are given for depth, velocity, dry weight of plant detritus and wet weight of macroinvertebrates. 161 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

During the study period, average air temperature and monthly precipitation (measured at Eniwa Shimamatsu Observatory, 13 km north-east of the

study site) ranged from -6.4-22.8•Ž and 20-396 mm, respectively (Fig.

Fig. 1. Meteorological parameters at Eniwa Shimamatsu Observatory , 13 km north- east of the study site, from Sapporo Meteorological Observatory (1993-1996) . A, Throughout the study period. B, During adult-flight period , 1994.

1A). 162 ITO

Adults

Adults were collected with a Malaise trap (180 cm wide, 180 cm high, mesh size 1 mm, across the stream) from 1 June to 10 November 1994. The collecting bottle was changed every 10 days. The adults were preserved in about 80% ethyl alcohol, and identified and counted under a dissecting microscope in the laboratory. Reproductive organs of P. shikotsuensis were observed under the dissecting microscope, and the females were classified into 5 stages modified from

GOWER (1967) : in stage A (the newly emerged female), the reproductive system is still small ; in stage B (the maturing female), eggs are almost completely developed but still in the ovariole ; in stage C (the mature female before oviposition), fully developed eggs are seen in the oviduct; in stage D1 (partly oviposited), some eggs still remain in oviduct but the abdominal cavity is partly empty; in stage D2 (after oviposition), the cavity is almost empty. Eggs of females in stages C and D1 were counted under the dissecting microscope.

Egg masses

The presence of egg masses was checked on 70 cobbles and 70 samples of wood debris on 15 June 1994. The status of the substrata (completely submerged or partly submerged) and their size (length of long axis for cobbles, and diameter at mid point and length for wood debris) were recorded. The egg mass position, depth or height from the water surface, was also recorded. Three egg masses were reared to larvae in the laboratory to confirm the field identifications.

Since total precipitation was 1 mm at the Eniwa Shimamatsu Observatory during 1-15 June 1994 (Fig. 1B), the water level of the stream had scarcely fluctuated before the observation.

Larvae, prepupae and pupae

Larvae, prepupae and pupae were collected on 9 June, 14 August, 16 October and 4 December of 1995, and on 3 April and 4 June of 1996.

Macroinvertebrates including P. shikotsuensis were taken from the submerged leaves and stems of living Kuril bamboo (Sasa kurilensis MAKING et

SHIBATA, referred to as S below), submerged leaves of other living terrestrial plants (mostly the Japanese butterbur, Petasites sp.) (L), woody debris (W) and riffles (R). However, samples of L were not collected from December to the following June, since the substratum was absent.

Five samples were taken from each substratum type. Quantitative samples were collected on a 25 cm•~25cm area with a Surber net (0.33 mm mesh) from S, L and R. In site W, the collecting procedure was as follows : woody debris was gently lifted out, placed in the Surber net, and washed down with 5 buckets of water. Retreat-making caddisflies were hand-picked with forceps. The collection area in W was calculated from the length •~ƒÎ the diameter in the middle of the wood debris.

Since the collection area in W was calculated in a different way from other 163 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

substrata, a quantitative comparison of density between W and the others might be impossible. Thus, the density of larvae shown under the (W) symbol is a rough comparison.

Macroinvertebrates were preserved in 5% formalin for later analyses. In the laboratory, larvae, prepupae and pupae of P. shikotsuensis were picked out. Head widths of larvae (across eye spots) were measured with an ocular micrometer to the nearest 0.01 mm, and the larvae were weighed wet to the nearest 0.1 mg with an electric micro-balance (Sartorius 1712 MP8, Zeiss

Co., Ltd.).

Wet weights of macroinvertebrates of each sampling, which were weighed to the nearest 0.1 mg with the micro-balance, were high from October through April (Table 1). Plant detritus, which was collected together with the macroinvertebrates at each sampling and weighed to the nearest 1 mg after a 96-h drying period at 100-110•Ž, was abundant in October and

December (Table 1). The water depth and velocity of each substratum collected were 1-27 cm and 9-99 cm S-1, respectively (Table 1).

Gut contents

Observations were made of the gut contents of up to 10 larvae of P. shikotsuensis for each instar, together with the substratum and month. The method of observation basically followed SHINMYO (1995). About the anterior one-third of the guts of fourth and fifth instar larvae and the whole guts of first, second and third instar larvae were put on microscope slides. Contents of the guts were separated, distributed with forceps and spindle on the slides, and mounted with "Mountmedia" (Wako Pure Chemical Indus- tries Co., Ltd.). Gut contents were classified into 5 categories ; animal fragments, vascular plant fragments, attached algae, mineral particles, and unidentified substances. The relative area occupied by each category was measured as follows : the outline of each fragment was traced using the drawing tube of a microscope with magnifications of 100-200. The relative areas of the 5 food categories were then calculated with a digitizer (Cosmo- zone 98, Nikon Co., Ltd.) to the nearest 1%. Ten microscopic views were observed for each larva and the average frequency of the 5 categories was used for analysis.

RESULTS

Adults

Adult numbers collected by a Malaise trap in 1994 and meteorological parameters during adult-appearance periods were shown in Figures 2A and 1 B, respectively. Adults appeared from early June to mid-August with a maximum number in mid-July. They decreased remarkably once in early

July (Fig. 2A) during bad weather (Fig. 1B). The capture of two males in the first sampling period (1-10 June) suggested that a few adults may emerge before 1 June. During operation of the trap, 43 males and 78 females of P. shikotsuensis were caught from 1 164 ITO

Fig. 2. Adults of Parapsyche shikotsuensis caught by a Malaise trap in 1994. A, N umber of males and females. B, Number of females with 4 stages. (B), the maturing female ; (C), the mature female before oviposition (Dl), partly oviposited ; (D2), after oviposition. C, Number of eggs of the females in stages C and Dl.

June to 20 August, with males being significantly fewer than females (x2 test, p<0.01). The first and last appearances of males were, respectively,. 10 days and 30 days earlier than those of females. The number of females in different developmental stages was shown in Figure 2B. Females in stage A were not collected, and females in stages B and C mostly occurred in the early half of the appearance period. Females in stages D1 and D2 were collected from the first 10 days and second 10 days of their appearance periods, respectively, indicating that females may deposit eggs soon after emergence. Moreover, since many females in stage D1 were collected, this species may mostly deposit eggs on at least two separate occasions. Egg numbers of females in stages C and D1 were shown in Figure 2C. Females in stage C had 488-634 eggs with a mode at 500-600 (average 564.6, SD 49.0, n=14), and females in stage D1 had 31-435 eggs with a mode at 0-100 (average 146.7, SD 108.0, n=33).

Egg masses Observations of egg masses on 70 cobbles and 70 pieces of wood debris were shown in Figure 3. Egg -masses were found on both partly and completely submerged cobbles 10-20 cm long (Fig. 3A) and 2-5cm underwater (Fig. 3B). They were also found underwater on completely submerged wood debris and above water on partly submerged wood debris 100-250cm long (Fig. 3C, D). On the partly submerged wood which was lying slantwise in the stream, egg masses were found only on the under surface. No egg masses were found on small cobbles (under 10cm in the long axis), thin wood debris (3-4cm in diameter) or short wood debris (under 50cm long). It is concluded that, on cobbles (completely and partly submerged) and completely submerged wood debris, egg masses were observed only underwater, whereas on partly submerged wood debris they were found only above water. 165 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

Fig. 3. Number of egg masses of Parapsyche shikotsuensis on various sizes and conditions of cobbles (A, B) and on wood debris (C, D). A and C, Number of observed substrates (total height of bars) and number of egg masses (solid parts). B and D, Number of egg masses and water depth and/or height above water. 166 ITO

On the observation date, five females had oviposited on emerged wood debris, and two live females were found on the underside of submerged cobbles. Moreover, a dead female was collected from the underside of cobbles with her abdomen lightly adhering to the egg mass with a gelatinous substance. Hence, it is certain that P. shikotsuensis females deposit eggs either above water or underwater on wood debris, and underwater on cobbles in the stream.

Instar of larvae Head widths of 387 P. shikotsuensis larvae fell clearly into 5 separate size classes (Fig. 4), suggesting 5 instars with ranges of : 0.34-0.38 mm, 0.54- 0.78 mm, 0.86-1.06 mm, 1.22-1.68 mm and 1.84-2.48 mm.

Fig. 4. Distribution of head width of Parapsyche shikotsuensis. I-V, instar of larvae.

Life cycle The relative abundance of 5 instar larvae, prepupae and pupae were shown in Figure 5A. The first to third instar larvae were collected in August and developed rapidly in autumn. The first and second instar larvae disappeared in October, and the fourth and fifth instar larvae first appeared in October . The relative abundance of fifth instar larvae gradually increased , i, e., from about 45% in October, to about 60% in December and about 85% by next April. They developed even in winter . Pupae and prepupae occurred in June. Thus, this species was evidently univoltine , with an early and mid-summer adult period.

Growth The seasonal changes in the wet weight of larvae, prepupae and pupae were shown in Figure 5B. The average weight was about 0 .2 mg for the first instar larvae and about 0.8 mg for the second . The averages were about 2 mg and 4 mg for the third in August and October , respectively, and 11-20mg 167 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

Fig. 5. Development and growth of Parapsyche shikotsuensis. A, Seasonal changes in frequency of 5 instar larvae (I-V), prepupae (PP) and pupae (PU). Small figure on solid histogram shows total number examined. Adult-appearance period is represented by a broken line based on the Malaise sampling in 1994. B, Seasonal changes in wet weight of immature stages. I-V, PP, PU as in A. for the fourth from October through next April. The averages for the fifth instar larvae were about 40 mg at their first appearance in October and 80 mg at their final one in June. The wet weights of prepupae and pupa were 57-67 mg and 76 mg, respectively. The average weights of the larvae increased even in winter, i. e., 11 mg in December to 21 mg by next April for the fourth instar larvae, and 49 mg in December to 71 mg by next April for the fifth instar larvae (at a 0.001 significance level in the t test for both instar larvae). They grew even in winter. 168 ITO

Substrata inhabited by larvae The density of 5 instar larvae at the 4 substrata and the results of ANOVA (at a 0.05 significance level in the SCHEFFE test) were shown in Figure 6. First instar larvae were 0-15 m-1 on average, and no significant differences were detected among the 4 substrata. Second instar larvae were ca. 20-80 m-1 on average , and their density in R was significantly higher than those in S and M. Third instar larvae were ca. 50-260 m-1 on average, and their density in R was significantly higher than the others in August. By October, however, they fell to 10-30 m-1 on average, and no significant differences were detected among the 4 substrata. Fourth instar larvae were ca. 5-20 m-1 on average, and no significant differences were detected among the 4 substrata. Fifth instar larvae were 5-25 m-1 on average, and their density in R was significantly higher than that in L. This suggests that second, third, and fifth instar larvae may prefer R.

Fig. 6. Average density (+1SD) of larvae of Parapsyche shikotsuensis on the 4 substrata. F values with* and*** are significant at 0 .05 and 0.001 levels, respectively. Substrata with same letters on top of bars are not significantly different at 0 .05 level in the SCHEFFEtest. 169 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

As stated above, this conclusion should be viewed with caution, since calculation methods in the collection area are differed between W and the other substrata.

Gut contents of larvae Mineral particles were completely absent, and attached algae were very scarce in the guts of larvae. Unidentified substances were only found in the guts of a few first instar larvae. The gut contents of larvae were mostly composed of animal fragments and vascular plant fragments. Paraleptoph- lebia spp., Ephemerellidae, Nemouridae, Chironomidae and Oligochaeta were often found in the guts. The relative abundance of animal fragments and the results of ANOVA (at a 0.05 significance level in the SCHEFFE test with aresine transformation) were shown in Figure 7. The average frequency of animal fragments was 69% in the first instar larvae, 80-90% in the second, third and fifth instar larvae, and 63% in the fourth instar larvae (Fig. 7A). Significant differences were detected between the fourth instar larvae and each of the second, third and fifth instar larvae. A comparison among larvae inhabiting the 4 substrata revealed no significant differences (Fig. 7B). The average frequency of animal fragments was over 90% in August 1995, April 1996 and June 1996, but significantly lower (about 60%) in October 1995 (Fig. 7C). In the guts of third instar larvae, the average frequency of animal fragments was about 90% in August which was significantly higher than frequencies in October and December (Fig. 7D). In the fourth instar larvae, the average frequency was about 55% in October, 65% in December, and over 95% in April, and a significant difference was detected between the frequency in April and those of the previous 2 months (Fig. 7E). In the fifth instar larvae, the average frequency was about 65% in October, about 90% in December, and 95% or more in April and June (Fig. 7F). A significant difference was found between October and the other 3 months. Thus, the frequency of animal fragments in the gut contents was low in October in third and fifth instar larvae, and low in both October and December in fourth instar larvae.

DISCUSSION More than 27 species of Parapsyche are distributed in East Asia and North America (WIGGINS, 1996). All such species hitherto studied are mostly predacious (MALAS and WALLACE, 1977; BENKE and WALLACE, 1980; HAEFNER and WALLACE, 1981; TANIDA, 1982; DUDGEONand RICHARDSON, 1988), inhabiting riffles, wood debris and bed rocks, and univoltine with a relatively long adult flight period in summer (BENKE and WALLACE, 1980; DUDLEY and ANDERSON, 1982; HURYN and WALLACE, 1988; MALAS and WALLACE, 1977; SINGH et al., 1984). P. shikotsuensis is essentially similar to them in its life. 170 ITO

Fig. 7. Average frequency (•|1SD) of animal fragments in the guts of Parapsyche shikotsuensis larvae. F values with*, ** and *** are significant at 0.05, 0.01 and 0.001 levels, respectively. Frequency with same letters on top of bars is not significantly different at 0.05 level in the SCHEFFE test after aresine translation.

Meteorological conditions during study peirod Adults and immature stages of P. shikotsuensis were collected from June through November 1994, and from June 1995 through June 1996 , respectively. Meteorological conditions between June 1993 to June 1994 (referred 171 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

to as '1993-1994' below), when the immature stages had been growing into

the adults of 1994, were compared with those from June 1995 to June 1996

('1995-1996'). At Shimamatsu Eniwa Observatory, 13 km from the study site, the

accumulated air temperature (excluding sub-zero) was a little lower in

' 1993-1994' (96.1•Ž month) than in '1995-1996' (111.1•Ž month) (Fig. 1 A). This difference may affect the growth rate, development rate and size

of each stage, but should not influence voltinism, since this species needs one

year to complete its life cycle. Total precipitation was similar in '1993- 1994' (1,060 mm) and in '1995-1996' (1,166 mm) (Fig. 1A), and no catastrophic flood occurred in these years.

So, I discuss some biological aspects of P. shikotsuensis based on adult

collecting in 1994 and immature collecting in '1995-1996'.

Substrata inhabited by larvae

Until recently, the submerged leaves and stems of living terrestrial plants had been overlooked as habitats of aquatic insects (i. e., WARD, 1992), until

ITO (1996) showed that many aquatic macroinvertebrates, including P.

shikotsuensis larvae, colonized the substratum of a headwater stream in

early winter. This study showed that this species lives on the substratum throughout its larval stage (Fig. 6), i, e., throughout the year. Thus, we

should survey the substratum in further ecological studies of mountain

streams.

Gut contents of larvae

Parapsyche larvae were primarily predacious, and the frequency of animal

fragments in their guts gradually increased with larval development (MALAS

and WALLACE, 1977 ; TANIDA, 1982). P. shikotsuensis larvae were also mostly predacious, and the average frequencies of animal fragments were

about 69% at the first instar larvae, 80-90% at the second, third and fifth instar larvae, and 63% at the fourth instar larvae (Fig. 7A).

Plant-detritus feeding by very early instar larvae of predacious species is well known (WIGGINS, 1996), but the lower frequency of animal fragments in the guts of fourth instar larvae of this species contradicted this tendency.

In comparison with the larvae collected in each of 5 months, the animal- fragment frequency was low in October (Fig. 7C) . Moreover, third, fourth and fifth instar larvae also showed low animal frequencies in October (Fig.

7D-F). Thus, it seems in the present species that the animal frequency in the guts may be essentially low in October regardless of the instar.

This lower frequency of animal fragments in fall was also observed in a

North American species, P. cardis Ross (MALAS and WALLACE, 1977), i.e., the animal-fragment frequency of the gut contents temporarily decreased in fall in the fourth and fifth instar larvae, although the decrease was not analyzed statistically nor discussed.

In December, when plant detritus was as abundant as in October (Table 1), the animal frequency increased in fifth instar larvae (Fig. 7F), although 172 ITO not in third or fourth instar larvae (Fig. 7D, E). This suggests that fifth instar larvae may choose higher quality food for successful metamorphosis.

Adult-appearance period and sex ratio The adult ecology of the genus Parapsyche has been studied for the appearance period and sex ratio of some North American species (BENKEand WALLACE,1980; HURYNand WALLACE,1988; SINGHet al., 1984) and the ovipositional behavior of. 2 Japanese species (KURANISHI,1992). Males of P. apicalis (BANKS), a North American species, appeared distinctly earlier (over 1 month) and were significantly more numerous than females in emergence traps (SINGHet al., 1984). Protandry was also suggested for the present species, but the sex ratio was the reverse of P. apicalis (Fig. 2A). The difference in sex ratio may be attributable to the collecting methods, because uneven sex ratios in Malaise collections are usually due to uneven flight activity (SVENSSON,1974 ; SODE and WIBERG-LARSEN,1993). The actual sex ratio should determined by the observation of pupae or by a direct catch of emerging adults.

Multiple oviposition KURANISHI(1992) reported the egg-mass size of this species in the field, which ranged from below 100 to 1600 with 2 extremes at 0-100 and 400 -500 . Based on the observation of female batches (about 600 on average), he presumed that the big (over 700) masses might be a combination of 2 or 3 egg masses, and that the small (below 100) masses might be due to interference during oviposition by predators or other accidents. In the present study, multiple oviposition was suggested by the presence of many females which oviposited only partly (stage D1 in Fig. 2B, C). In addition, egg numbers of the females in stage D1 showed a mode below 100 (Fig. 2C), suggesting that small egg masses in the field (KURANISHI,1992) are usually a second or later oviposition. The detailed processes of maturation and oviposition, and the ecological significance of ovipositional behavior in this species largely remain subjects for further studies.

Oviposition site KURANISHI(1992) stated that females of P. shikotsuensis deposit eggs only on wet areas above water and do not submerge. However, the present study clearly showed that underwater oviposition was an ordinary behavior in addition to above-water oviposition in this species, since egg masses were present on the underside of submerged cobbles (Fig. 3), and two live and one dead females were found on the underside of stones in the water. The egg masses were present only on the underside of above-water parts of slantwise emerging wood (Fig. 3B) where the surfaces were always both dark and wet. Since the above-water parts of partly submerged cobbles are light and dry quickly, the females may deposit eggs only underwater on partly submerged cobbles. The egg masses were never found underwater on partly submerged wood 173 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

(Fig. 3D). This observation may suggest that ovipositing females prefer the wet area above water rather than underwater when both are available. KURANISHI'S (1992) study site was an artificial water-course where the flow was narrowed with boards and many boulders were put into the stream to protect against bank erosion. The flow was deep (usually over 50 cm) and rapid (over 1 m S-1 at maximum) and splashing was frequent on the boards and boulders. Stagnant areas were rare. On the other hand, in the present site, the flow was much slower (Table 1) and splashed areas of firm substrata were scarce, since the stream bank mostly consisted of mud covered with moss, riparian weeds, and the roots of riparian trees. These circumstantial differences may have an effect on the egg mass sites of P. shikotsuensis, i, e., if splashed firm substrata are luxuri- ous and water flow is very rapid, the females may deposit on the substrata above water, but if they are scarce and the flow is moderately gentle, they may deposit their eggs on substrata under the water. Thus, it seems that P. shikotsuensis females may have options in their oviposition sites depending on the circumstances. The larvae of Parapsyche are characteristically found in small, cold, swift streams (WIGGINS, 1996). Their restricted distribution may be partly due to female ovipositional preference, since their favorite areas, i, e., dark, wet substrata splashed by flowing water, are generally abundant in small, swift mountain streams.

ACKNOWLEDGEMENTS I am most grateful to Mr. N. KUHARAof the Chitose Board of Education for his help on statistical analysis, and to Mr. T. NOZAKI of the Kanagawa Environmental Research Center for his help on searching out references and his expertise in the female maturation process of Trichoptera.

REFERRENCES BENKE, A. C. and J. B. WALLACE(1980): Trophic basis of production among net-spinning caddisflies in a southern Appalachian stream. Ecology, 61: 108- 118. DUDGEON,D. and J. S. RICHARDSON(1988): Dietary variations of predaceous caddisfly larvae (Trichoptera: Rhyacophilidae, Polycentropodidae and Arc- topsychidae) from British Columbian streams. Hydrobiologia, 160: 33-43. DUDLEYT. and N. H. ANDERSON(1982): A survey of invertebrates associated with wood debris in aquatic habitats. Tech. Rep. Oregon Agr. Exp. St., 6419: 1-21. GOWER,A. M. (1967) : A study of Limnephilus lunatus CURTIS (Trichoptera: Limnephilidae) with reference to its life cycle in watercress beds. Trans. R. Ent. Soc. Lond., 119: 283-302. HAEFNER,J. and J. B. WALLACE(1981): Production and potential seston utiliza- tion by Parapsyche cardis and Diplectrona modesta (Trichoptera: Hydro- psychidae) in two streams draining contrasting southern Appalachian water- 174 ITO

sheds. Environ. Ent., 10 : 433-441. HURYNA. and J. B. WALLACE(1988) : Community structure of Trichoptera in a mountain stream : spatial patterns of production and functional organization. Freshwat. Biol., 20 : 141-155. ITO, T. (1996) : A preliminary survey of macroinvertebrates associated with submerged leaves and stems of terrestrial plants in a headwater stream of northern Japan. Biol. Inl. Wat., 11 : 12-19. KURANISHI,R. B. (1992) : Above-water oviposition of two Japanese Parapsyche species (Trichoptera: Hydropsychidae). In Proc. 6th Int. Symp. Trichoptera, C. TOMASZEWSKI(ed.) : 148-152. Adam Mickiewicz Univ. Press, Poznan. MALAS,D. and J. B. WALLACE(1977) : Strategies for coexistence in three species of net-spinning caddisflies (Trichoptera) in second-order southern Appala- chian streams. Can. J. Zool., 55 : 1829-1840. Sapporo Meteorological Observatory (ed.) (1993-1996) : Weather of Hokkaido, No. 484-No. 519. Hokkaido Office of Meteorological Association, Sapporo (in Japanese). SHINMYO,F. (1995) : A food web of benthic community in a Japanese mountain stream (Takamigawa, Nara) and its dynamic aspects. In Report of the grant-in-aid for general scientific research (No. 05640714) on "Synthesis of taxonomical and ecological knowledge on lotic insects in Japan" from the Japan Ministry of Education, Science and culture, K. TANIDA(ed.) : 60-69. Tokyo (in Japanese). SINGH, M. P., S. M. SMITHand A. D. HARRISON(1984) : Emergence of some caddisflies (Trichoptera) from a wooded stream in southern Ontario. Hydrobiologia, 112: 223-232. SODE A. and P. WIBERG-LARSEN(1993) : Dispersal of adult Trichoptera at a Danish forest brook. Freshwat. Biol., 30 : 439-446. SVENSSON,B. W. (1974) : Population movements of adult Trichoptera at a South Swedish stream. Oikos, 25 : 157-175. TANIDA,K. (1982) : Ecology of caddisflies. The Nature and Insects, 17 (8) : 7-11 (in Japanese). WARD,J. V. (1992) : Aquatic insect ecology 1. Biology and habitat. John Wiley & Sons, New York. WIGGINS, G. B. (1996) : Larvae of the North American caddisfly genera (Trichoptera). Second edition. Univ. Toronto Press, Toronto.

Tomiko ITO:Hokkaido Fish Hatchery, Kita-kashiwagi, Eniwa, Hokkaido, 061- 1433Japan(伊藤富子:〒061-1433北海道恵庭市北柏木町3-373北海道立水産ふ化場)

(Received: 28 January 1998; Accepted: 7 December 1998) 175 Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis

北海道の一源流におけるシコツシマトビケラ

Parapsyche shikotsuensisの生活史

伊藤富子

摘要

1994-1996年に北海道恵庭市漁川水系の源流において,シコツシマトビケラParapsy- c he shikotsuensis (IWATA)の生活史を調べた。この種は明瞭な年1化であり,成虫は6-8 月に出現し,水面上と水中の石や倒木に卵塊を産み付けていた。その子孫は秋のうちに急速に成長し,10月までに3齢以上になり,ほとんどのものが5齢(終齢)になって冬を迎えた。冬の間も幼虫は発育し体重も増加した。幼虫はササなど河畔植生の水に浸かっている葉や茎,倒木,瀬に生息しており,2齢,3齢,5齢幼虫の密度は瀬でやや高かった。消化管内容物は55-95%が動物の砕片で,残りは維管束植物であった。動物質の割合は,齢間の比較では4齢幼虫で低く,採集時期間では10月に低く,採集した基質問では差がなかった。また,3,4,5齢幼虫について月間で比較したところ,10月には動物質の割合の低い傾向が共通して認められた。