Proceedings of the 11 th International Symposium on Trichoptera (2003, Oaaka) pages 37 1-38 I , O 2005 Tokai University Press, Kanagawa. eds. K. Tanida and A. Rossiter

Caddisflies (Insecta: Trichoptera) collected from the Bonin Islands and the Izu Archipelago, Japan

Kiyoshi SATAKE', Ryoichi B. KURANISHI~ and Ryuhei UENO'

' National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan; Natural History Museum and Institute, Chiba, Chiba 260-8682, Japan

Abstract. Caddisflies collected from the Bonin Islands and the Izu Archipelago, Japan, during 1991- 2001 were identified to twelve species belonging to ten families. Three of the ten species collected from the Izu Archipelago are conspecific with those of Honshu, the main island of Japan, whereas one out of two species from the Bonin Islands shows a disjunct distribution with its closely related species, and is regarded as an endemic species. The male and female of Goera ogasawaraensis new species from Chichi Island, the Bonin Islands, are described.

Introduction

The Izu Archipelago and the Bonin Islands (or the Ogasawara Islands) are located between ca. 50 km and 1,100 km south of Honshu, the main island of Japan (Fig. I), and belong to Tokyo Metropolitan Government administrative- ly.

Most of these islands are oceanic, located on submarine ridges parallel with the Izu-Bonin Trench, where the Pacific Plate is subducted below the Philippine Sea Plate. The Izu Archi- pelago is composed of Quaternary volcanic islands, some of which are still active, as in the case of Miyake Island. The Bonin Islands are of Tertiary submarine volcanic origin, but it is not known how these islands were uplifted.

Even if the Izu Archipelago is presently sep- arated from Honshu by seas deeper than 200 m, it is a controversial issue as to whether these islands were connected with Honshu by land-bridges during the sea level falls during glaciallinter- glacial cycles of the Quaternary. One recent interpretation (Araya 2001) is that, even if the land-bridges were not present, the sea between the archipelago and the mainland would be like a narrow strait, which enabled some of mainland biota to enter the islands easily.

Conversely, the Bonin Islands, separated from Honshu and the other larger land masses by seas deeper than 3,000 m, are regarded as true oceanic islands, which have never been connect- ed with continents and continental islands. These islands support a high endemism in some plant and animal groups, and have consequently been referred to as the "Galapagos of the Northwest Pacific" (Miiller-Dombois and Fosberg 1998).

Although many entomologists (e.g. Gressitt 1954; Nakane 1970; Kurosawa 1978; Makihara 1988; Kato 1992; Araya 2001) have studied the insect fauna of the Izu Archipelago and that of the Bonin Islands, only Tomokuni and Sato (1978) reported on the Trichoptera fauna of the Bonin Islands.

The purpose of this study is to reveal the Trichoptera fauna of Izu-Bonin area, and to deter- mine the taxonomic position of Goera sp. record- ed by Tomokuni and Sato (1978).

Study Sites

Caddisfly larvae, pupae and adults collected from the Izu Archipelago (Kouzu Island, Miyake Island, Mikura Island and Hachijyo Island) and the Bonin Islands (Chichi Island and Haha Island) are used for this study.

Collection sites of Trichoptera on each island are shown in Fig. 2. Latitude, longitude and altitude of each site was determined by checking its position on "Digital Map 25000", based on the WGS84 (World Geodetic System 1984) coordinate system, issued by the Geo- graphical Survey Instit~~te, Japan (2003).

The distance of each island is a value, esti- mated by Tokyo Metropolitan Government (TMG) between its Metropolitan Buildings and a village or town office in each island. The popula- tion of each island in the Izu Archipelago is based on the "National Census" conducted by the Statistics Bureau, Japan in 1995 and 2000, whereas that of Chichi Island and Haha Island is based on a monthly report by Ogasawara Village Office.

The Izu Archipelago is located in the tem-

Kiyoshi SATAKE, Ryoichi B. KURANISHI and Ryuhei UENO

Fig. I . Map of the Izu Archipelago and the Bonin Islands. Shima and jima mean island in Japanese.

perate zone. The annual mean temperature ranges from 15.1 to 18. 1°C, and the annual pre- cipitation ranges from 2,850 to 3,130 mm.

The Bonin Islands are located in the sub- tropical zone. The annual mean temperature in Chichi Island can reach 23.0°C, and the annual precipitation is 1,260 mm, less than half that of the Izu Archipelago.

Kouzu Island An active volcanic island; recent volcanic

activity: in 838 (AGCJ 1996, Kaizuka et al. 2000); area: 18.9 km2; highest elevation: 571.5 m a.s.1.; location: 178 km south-southwest of TMG; administration: Kouzu-shima Village; population: 2,144.

Kz-1. A small stream near Sawajiri Bay, ca. 100 m from its river mouth, 34"12'59"N, 139"08'06"E, 30 m a.s.1.

Miyake Island An active volcanic island; recent volcanic

activity: 1940, 1962, 1983 (AGCJ 1996) and "the 2000 eruption"; area: 55.5 km2; highest elevation: 813.7 m a.s.1.; location: 186 km south of Tokyo; administration: Miyake Village; population in 1995 and 2000: 383 1 and 0, respectively.

Mye- 1: A small stream just south of Tairo Pond, with a stream bed full of volcanic black sand, 34"02'56"N, 139"3 1'4S7'E, 20 m a.s.1. Mye-2: A small temporary stream with pools and hygropetric habitats, near Igaya logging road, 34"05'36"N, 139"30'06"E, 320 m a.s.1.

Mikura Island An active volcanic island; recent volcanic

activity: ca. 5,000 years ago (Kaizuka et al. 2000); area: 20.6 km2; highest elevation: 850.9 m a.s.1.; location: 200 krn south of Tokyo; adminis- tration: Mikura-jima Village; population: 308.

Mk-2a: Upper reaches of the Eiga River, 33"52'06"N, 139"37'08"E, 480 m a.s.1. Mk-3: A small spring under the Eiga River Bridge, Nangou, 33"51'54"N, 139"37'25"E, 250 m a.s.1. Mk-5a: Headwaters of Ohshimawake River (a river of spring water origin), 33"52'43"N, 139"36'47"E, 380 m a.s.1. Mk-6: Upper reaches of Ohshimawake River near the hydroelectric power station, 33"53'06"N, 139"37'07"E, 180 m a.s.1. Mk-8: Nishikawa Spring, Nishikawa, 33"52'34"N, 139"35'28"E, 140 m a.s.1. Mk-11: Boro River, 33"52'51"N, 139"35' 18"E, 390 m a.s.1. Mk-13: A nameless stream with pot holes, 33"52'32"N, 139"35'117'E, 410 m a.s.1. Mk-13b: Downstream of Mk-13, 33"52'36"N, 139"35'07"E, 350 m a.s.1. Mk-15b. A small stream, just downstream of an

Caddisflies (Insecta: Trichoptera) collected from the Bonin Islands and the Izu Archipelago. Japan

u

. 2. Maps of islands with study sites and contour lines. Shima and jima mean island.

Kiyoshi SATAKE, Ryoichi B. KURANISHI and Ryuhei UENO

erosion control dam, 33"52'25"N, 139"35'16"E, 430 m a.s.1. Mk-16: A small stream north of "Ebine P a r k , a center for restoring endangered Calanthe species, 33"52'01HN, 139"35'19"E, 510 m a.s.1. Mk-17: A small stream south of "Ebine Park", 33"51'59"N, 139"35'21mE, 520 m a.s.1.

Hachijyo Island An active volcanic island; recent volcanic

activity: in 1605 at the western mountain (Kaizu- ka et al. 2000); area: 69.5 km2; highest point: 854.3 m a.s.1 (the western mountain); location: 287 km south of Tokyo; administration: Hachijyo Town; population: 9,488.

Hc-1: Upper reaches of the Oh River, near a log- ging road, 33"06'04"N, 139"48'52"E, 320 m a.s.1. Hc-2: A branch of the Kamo River, near a log- ging road, 33"05'49"N, 139"48'15"E, 290 m a.s.1. Hc-3: Upper reaches of the Kamo River, near a logging road, 33"05'49"N, 139"48'08"E, 290 m a.s.1. Hc-4: Middle reaches of the Oh River, 33"06'36"N, 139"48'33"E, 120 m a.s.1. Hc-5: Middle reaches of the Kamo River, 33"06'14"N, 139"48'11"E, 100 m a.s.1. Hc-6: Middle reaches of the Mihara River, 33"04'01 "N, 139"49'02"E, 130 m a.s.1.

Chichi Island An island formed from submarine volcanic

products; area: 24.0 km2; highest point: 326.0 m a.s.1.; location: approximately 1,050 km south of Tokyo; administration: Ogasawara Village; popu- lation: 1,930.

Ch-1: Upper reaches of the Okumura River, 27"05'57"N, 142"12'41HE, 50 m a.s.1. Ch-2: A head-water stream of the Yasse River, near the ruins of the imperial army field hospital, Ohtaki, 27"03'55"N, 142"13'08"E, 210 m a.s.1. Ch-3: A nameless small stream near Kopepe Beach, 27"03'55"N, 142"1 1137"E, 10 m a.s.1. Ch-5: Minamifukuro River, ca. 200 m from the river mouth, 27"03'23"N, 142"l 1135"E, 5 m a.s.1. Ch-6: Minamifukuro River, ca. 1,000 m from the river mouth, 27"03'10nN, 142"l 1154"E, 20 m a.s.1. Ch-8: A nameless small stream near Hinkou Bridge, 27"05'13"N, 142"12'27"E, 20 m a.s.1. Ch-14b: A headwater stream in Renjyu Valley, 27"04'14"N, 142"12'44"E, 130 m a.s.1. Ch-23: A small stream near Tenno-ura Bay,

upstream of Tenno-ura Fall, 27"02'33"N, 142"13'10"E, 90 m a.s.1.

Haha Island An island formed from submarine volcanic

products; area: 20.8 km2; highest point: 462.6 m a.s.1.; location: approximately 1,100 km south of Tokyo; administration: Ogasawara Village; popu- lation: 445.

Ha-2: A nameless small stream near Koushin- zuka Mound, 26"41'07"N, 1 42"08'33"E, 130 m a.s.1. Ha-3: Upper reaches of the Nagahama River, near Nagahama Bridge, 26"40'25"N, 142"09'00"E, 130 m a.s.1.

List and descriptions of collected species

The arrangement of families follows Wig- gins (1996), and genera and species are arranged alphabetically within each family. Material which was only identified to generic level was nevertheless treated as individual species if it was clearly distinguishable from all other known species in the genus.

Collectors' names are abbreviated as fol- lows: KS: Kiyoshi Satake; RBK: Ryoichi B. Kuranishi; RU: Ryuhei Ueno.

In the following list, twelve species are recorded from the Bonin Islands and the Izu Archipelago. These are classified into ten fami- lies as follows. A single species was recorded for each of the Rhyacophilidae, Glossosomatidae, Psychomyiidae, Hydropsychidae, Lepidostomati- dae, Apataniidae, Goeridae and Helicopsychidae, and two species were recorded for each of the Hydroptilidae and Philopotamidae.

Type materials are deposited in the Natural History Museum and Institute, Chiba (CBM) and the National Museum of Natural History, Smith- sonian Institution, Washington, D.C. (NMNH). The materials collected by KS and RU are deposited in the National Institute for Environ- mental Studies, Tsukuba (NIES), unless other- wise stated. The other materials are deposited in CBM.

Suborder Spicipalpia

Family Rhyacophilidae

1. Rhyacophila sp.

Caddisflies (Insecta: Trichoptera) collected from the Bonin Islands and the Izu Archipelago, Japan

Material examined Mk-5a, four larvae, 16.111.2001, RU leg.

(four larvae are deposited in CBM).

Distribution Izu Archipelago (Mikura Island).

Remarks This species was only collected from the

headwaters of a spring stream, and seemed to belong to the Rhyacophila nigrocephala group.

Family Hydroptilidae

2. Scelotrichiu sp.

Material examined Mk-6, three final instar larvae, 18.111.2001,

KS leg. (one larva is deposited in CBM).

Distribution Izu Archipelago (Mikura-jima).

3. Hydroptilidae gen. sp. (Fig.3, Plate I)

Description Final-instar larva: Abdomen slightly com-

pressed laterally. Body length between 1.66 and 2.28 mm (n=ll). All three pairs of legs approxi- mately the same length (Fig. 3). Tarsal claws slender, sn~oothly curved in fore leg (Fig. 3A), abruptly curved in mid and hind legs (Figs. 3B, 3C), each with thick, pointed seta at base. Protib- ia with prominent posteroventral lobe bearing short, very stout setae (Fig. 3A). Abdominal seg- ments from I1 to VI with dorsal chloride epithe- lia. Three filamentous gills arising from posterior end of abdomen, one from dorsomedian position on segment IX, other two at lateral sclerites of anal prolegs. Claws on anal prolegs with three accessory hooks.

Case: Consisting of two silken valves cov- ered with sand grains, diatoms, filamentous algae and pieces of freshwater red algae. Length between 2.03 to 3.13 mm (n=ll).

Material examined Ch- 1, three pupae and 1 1 final instar larvae,

10.11.1998, KS and RU leg.; ibid., six pupae and 59 final instar larvae, 28.11.1999, KS and RU leg.; Ch-2, one final instar larva, 10.11.1998, RU leg.; Ch-3, 16 final instar larvae, 26.11.1999, KS and RU leg.; ibid., three pupae and nine final instar larvae, 4.VI.1999, KS leg.; Ch-5, one female, 11 .II. 1998, KS leg.; Ch-6, five early

instar larvae, 25.11.1999, KS leg.; Ch-8, one pupa and one final instar larva, 13.11.1998, RU leg.; ibid., one prepupa and 16 final instar larvae, 27.11.1999, RU leg.; Ch-23, two pupae, four final instar larvae and one early instar larva, 4.V.2000, KS leg.; Ha-2, three final instar larvae, 13.11.1998, KS leg.; Ha-3, one case, 13.11.1998, KS leg.

Distribution Bonin Islands (Chichi Island, Haha Island).

Remarks Early instar larvae were found only in asso-

ciation with the freshwater red algae, Batrachos- perumum sp. (Plate I-A), whereas final instar lar- vae occurred widely on stream beds. Some of the

0.1 mm A-C

Fig. 3. Larva of Hydroptilidae gen. sp. A. foreleg, later- al view; B. middle leg, lateral view; C. hind leg, lateral view.

Kiyoshi SATAKE, Ryoichi B. KURANISHI and Ryuhei UENO

Plate I. A-C: Hydroptilidae gen. sp. A. typical habitat of free-living early instar larvae; B. final instar larvae removed from cases; C. pupa (left), early instar larva (middle) and final instar larva (right). D-G: Goera ogasawaraensis: D, Goera japonica Banks (left) and Goera ogasawaraensis Kuranishi new species (right); E. pupa (left) and larvae; F. col- lection site of type specimens; G. aggregation of pupae.

Caddisflies (Insecta: Trichoptera) collected from the Bonin Islands and the Izu Archipelago, Japan

latter fasten their cases to bedrock surfaces.

Family Glossosomatidae

4. Glossosoma sp.

Material examined Mk-6, 38 larvae, 18.111.2001, KS and RU

leg.; Mk-13, one larva, 17.111.2001, KS leg.; HC- 1, 114 larvae, 11 .III.1999, KS leg.; Hc-2, one larva, 11.111.1999, KS leg.; Hc-3, 261 larvae, 11.111.1999, KS leg.; Hc-4, five larvae, 21 .VI. 1991, RBK leg.; Hc-5, two females, 21 .VI. 1991, RBK leg.; ibid, eight larvae, 8.X1.1992, S. Kanada leg.

Distribution Japan: Izu Archipelago (Mikura Island,

Hachijyo Island), Hokkaido, Honshu, Shikoku, Kyushu; Korea.

Suborder Annulipalpia

Family Philopotamidae

5. Chimarra sp.

Material examined Kz-1, six larvae, 18.VIII.1987, M.

Hasegawa leg.

Distribution Izu Archipelago (Kouzu Island).

6. Dolophilodes sp.

Material examined Mk-6, one larva, 18.111.2001, RU leg.

Distribution Izu Archipelago (Mikura Island).

Family Psychomyiidae

7. Psychomyiidae gen. sp.

Material examined Mye-1, one larva, 13.111.1999, KS leg.; Mk-

6, four larvae, 18.111.2001, RU leg.; Mk-13, one larva, 17.111.2001, KS leg.; Mk-17, one larva, 18.III.2001, KS leg.

Distribution Izu Archipelago (Miyake Island, Mikura

Island).

Family Hydropsychidae

8. Hydropsyche orientalis (Martynov)

Material examined Kz-1, two larvae, 18.VIII.1987, M.

Hasegawa leg.; Mk-6, 11 larvae, 18.111.2001, RU leg.; Mk-13b, five larvae, 17.111.2001, KS leg.; Hc-1, 12 larvae, 11.111.1999, KS leg.; Hc-4, 12 larvae, 2 1 .VI. 199 1, RBK leg.; Hc-5, four females and five larvae, 2 1 .VI. 199 1, RBK leg.; ibid, ten larvae, 8.XI.1992, S. Kanada leg.

Distribution Japan, Izu Archipelago (Kouzu Island,

Mikura Island, Hachijyo Island), Hokkaido, Honshu, Shikoku, Kyushu, Amami Island, Olu- nawa; Korea; Russia (south Ussuri).

Suborder Integripalpia

Family Lepidostomatidae

9. Lepidostoma japonica (Tsuda)

Material examined Kz- 1, two larvae, 18.VIII. 1987, M.

Hasegawa leg.; Mk-2a, one case, 18.111.2001, RU leg.; Mk-3, one case, 16.111.2001, KS leg.; Mk-6, 55 larvae, 18.111.2001, KS and RU leg.; Mk-8, one larva, 19.111.2001, KS leg.; Mk-1 1, one pre- pupa and eight larvae, 19.111.2001, KS leg.; Mk- 13, one prepupa and 34 larvae, 17.111.2001, KS and RU leg.; Mk-13b, eight larvae, 17.111.2001, KS and RU leg.; Mk-15b, eight larvae, 17.111.2001, RU leg.; Mk-16, 55 larvae, 18.111.2001, KS and RU leg.; Mk-17, 88 larvae, 18.111.2001, KS and RU leg.; Hc- 1, 89 larvae, 1 1 .III. 1999, KS leg.; Hc-2, 39 larvae, 1 1 .III. 1999, KS leg.; Hc-3, 70 larvae, 11.111.1999, KS leg.; Hc-4, Two larvae, 21 .VI.1991, RBK leg.; Hc-5, eight larvae, 8.XI.1992, S. Kanada leg.; Hc-6, one male and 18 larvae, 3 l.VIII.1993, N. Kobayashi leg.

Distribution Izu Archipelago (Kouzu Island, Mikura

Island, Hachijyo Island), Hokkaido, Honshu, Sado, Kyushu, Yaku Island.

Family Apataniidae

10. Apatania sp.

Material examined Mye-2, two larvae, 13.111.1999, KS leg.;

Mk-2a, one larva, 18.111.2001, RU leg.; Mk-6, 10 larvae, 18.111.2001, KS and RU leg.; Mk-8, three

Kiyoshi SATAKE, Ryoichi B. KURANISHI and Ryuhei UENO

cases, 19.111.2001, KS leg.; Mk-11, two larvae, 19.111.2001, KS leg.; Mk-13, seven larvae, 17.111.2001, KS and RU leg.; Mk-13b, four lar- vae, 17.111.2001, KS and RU leg.; Mk-16, six lar- vae, 18.111.2001, RU leg.; Mk-17, five larvae, 18.111.2001, KS and RU leg.; Hc-1, eight larvae, 11.111.1999, KS leg.; Hc-2, 12 larvae, 11.111.1999, KS leg.; Hc-3, 169 larvae, 1 1 .III. 1999, KS leg.; Hc-4, one larva, 21.VI.1991, RBK leg.; Hc-5, three larvae, 8.XI.1992, S. Kanada leg.

Distribution Izu Archipelago (Miyake Island, Mikura

Island, Hachijyo Island).

Family Goeridae

11. Goera ogasawaraensis Kuranishi, new species (Figs. 4-5)

Goera sp., Tomokuni and Sato, 1978, 117-118, larva and case.

Description Adult: Body dark brown, forewing brown

with dark brown hairs. Antenna1 scape of male 4.0 times as long as wide. Distal segment of maxillary palp oval, twice as long as wide. Ster- nite VI of male bearing short transverse array of spines, number of spines variable in specimens (Fig. 4-E). Length of body, Male, 4.29 mm - 4.72 mm (n=4); female, 4.42 mm (n=l). Length of forewing. Male, 5.28 mm - 5.94 mm (n=4); female, 5.45 mm - 6.27 mm (n=2).

Male genitalia (Fig. 4): Dorsum IX long in lateral view, with apicomesal process of sternum IX developed into rectangular lobe, at least four- fifths as long as main body of segment IX; pre- anal appendage slender, thin, and filamentous, with tapering apex. Ventorolateral branches of tergum X sclerotized, unbranched, long, and tapering to acute point. Basal segment of inferior appendage a parallelogram in lateral view; distal segment distinctly segmented from basal segment and bearing arcuate dorsal process with rounded

Fig. 4. Male of Goera ogasawaraensis Kuranishi, new species. A-D: genitalia. A. lateral view; B. dorsal view; C. ven- tral view; D. phallus, lateral view; Dd. phallus, dorsal view, E(1-3); array of spines on sternite VI. E l . specimen (CBM-ZI 94765); E2. specimen (CBM-ZI 94764); E3. specimen (CBM-ZI 94763).

Caddisflies (Insecta: Trichoptera) collected from the Bonin Islands and the Izu Archipelago, Japan

Fig. 5. Female genitalia of Goera ogasawaraensis new species. A. lateral view; B. dorsal view; C. ventral view.

apex, short ventral lobe, and arcuate mesa1 Immature stages process with tapering apices directed laterad in The larva and its case were described by ventral view. Phallus regular, tube-like with Tomokuni and Sato (1978) from Bonin Islands, phalicata membranous, without paramere; phallic Chichi Island as Goera sp. apodeme forming acute angule anteriorly.

Female genitalia (Fig. 5): Preanal appendage fused with tergum X, each triangular, 1.2 to 1.4 times as long as the width of the base in dorsal view; laterally appearing elongate, with subapical ventral swelling. Gonopod plate about 1.5 times as broad as the length, without api- comesal process in ventral view. Spermathecal plate generally oval-shaped, about 1.6 times as long as wide.

Diagnosis of adults This new species is closely related to Goera

japonica Banks from Japan (Honshu). The male of the new species is distinguishable from that of G. japonica by the following characters, (1) body size significantly smaller (Plate I-D), (2) number and shape of short transverse array of spines of sternite VI, (3) long dorsum IX, (4) basal seg- ment of inferior appendage a parallelogram in lat- eral view.

Holotype: Male, Tokyo, Bonin Islands, Chichi Island, upper stream of Shigure Barrage (Ch-2), 19.VI. 1991, S. Miyano leg, (CBM-ZI 94762). Paratypes: Three males and two females (CBM- ZI 94763-767), one male (NMNH), same data as holotype.

Other material examined: Ch-1, four larvae, 28.11.1999, KS leg.; Ch-2, two males, four prepu- pae, 13 pupae and 17 larvae, 19. VI.1991, S. Miyano leg. (same as holotype); ibid, seven lar- vae, 10.11.1998, KS and RU leg.; ibid, eight lar- vae, 3.VI.1999, KS and RU leg.; ch-14b, four larvae, Chichi Island, Renjyu Valley, 5. IV. 1989, T. Ito leg.

Japanese name Ogasawara-ningyo-tobikera.

Distribution Known only from Chichi Island, the Bonin

Islands.

Kiyoshi SATAKE, Ryoichi B. KURANISHI and Ryuhei UENO

Family Helicopsychidae disflies collected in the Izu Archipelago were the same as those occurring on Honshu. If the taxo-

12. Helicopsyche sp. nomic positions of the remaining species become clear, it is expected that the number of species

Material examined common to Honshu and the Izu Archipelago will Mk-6' One case' 18'111'2001' KS leg'' Mk- increase. The numbers of species occurring on

13, cases, 17'111'20013 KS leg'; Mk-17, five Mikura Island, Hachijyo Island, Kouzu Island cases, 18.111.2001, KS leg. and Miyake Island were nine, four, three, and Distribution

Izu Archipelago (Mikura Island).

Discussion

The Trichoptera fauna of the Bonin Islands and the Izu Archipelago has hitherto been investi- gated only by Tomokuni and Sato (1978).

We tried to document the Trichoptera fauna of the Izu-Bonin area. It was difficult to analyze the fauna of all these islands together because the fauna of the Izu Archipelago and that of the Bonin Islands was completely different in species composition (Table 1).

In the Bonin Islands one of two species of caddisflies collected, Goera ogasawaraensis, was not collected at any other areas, although a close- ly related species was found in Honshu and its adjacent area. Consequently, this species was regarded as an endemic. Furthermore, once the taxonomic position of the specimens tentatively attributed as Hydroptilidae gen. sp. has been clar- ified, this taxon is expected to also be endemic to this area.

In contrast, three out of ten species of cad-

two, respectively. If we assume the Trichoptera fauna of these

islands to be dependent on the immigration rate, the number of species present sl~ould be related to the distance between each island and the main- land, Honshu. However, the distance from Hon- shu is in the order of Kouzu Island (nearest island), Miyake Island, Mikura Island and Hachi- jyo Island, which does not accord with the num- ber of species present. This is partly a conse- quence of the limited sampling undertaken at Kouzu Island, for which results are regarded as underestimates.

If we assume that the Trichoptera fauna of the island groups is dependent on the extinction rate, the numbers of species should be related to the area and/or volcanic activity of each island. In terms of area, the islands can be ranked as Hachijyo Island (largest), Miyake Island, Mikura Island and Kouzu Island, respectively, whereas in terms of recent volcanic activity they can be ranked as Mikura Island (longest period since volcanic activity), Kouzu Island, Hachijyo Island and Miyake Island. It might be appropriate to consider that the species number of caddisflies

Table 1. The distribution of caddisflies in the Izu Archipelago and the Bonin Islands, based on the collections during 1991-2001. Species and islands are arranged according to the ordinations obtained by a correspondeilce analysis using the presence and absence dataset of caddisfly species in each island. *: species present, -: species absent.

Izu Archipelago Bonin Islands

Kouzu Hachijyo Mikura Miyake Chichi Haha

Chimarra sp. Hydropsyche orientalis Goerodes japonicus Glossosoma sp. Dolophilodes sp. Helicopsyche sp. Rhyacophila sp. Scelotrichia sp. Apatania sp. Psychomyiidae gen. sp. Goera ogasawaraensis Hydroptilidae gen. sp. Number of species

Caddisflies (Insecta: Trichoptera) collected from the Bonin Islands and the Izu Archipelago, Japan

within the four islands is related to the recency and frequency of volcanic activity, but we have to view this conclusion with caution until further surveys are conducted in Hachijyo Island and Kouzu Island.

Acknowledgements

We thank Dr S. Miyano, Natural History Museum and Institute, Chiba, Dr M. Hasegawa, Toho University, Mr T. Ito, Chiba University, Mr S. Kanada, Nippon Engineering College and Mr N. Kobayashi, Saitama Prefecture for their dona- tion of specimens.

We are indebted to Dr S. Nohara, Dr T. Natori and Dr T. Yabe, Ecosystem Study Section, National Institute for Environmental Studies, for their advice during the course of the study, and Dr T. Kagaya, Tokyo University, for encourage- ment and support. We thank Dr K. Horikoshi, Mr M. Inaba and Mr H. Suzuki, Institute for Boninology, for their help and guidance in Chichi Island; Mr H. Chiba, Ogasawara Village Office, and Mr Y. Hoshi, Villa Kobunoki, for their help and guidance in Haha Island; and Dr H. Hamada, Chiba University, and Dr H. Utagawa, Japan Society for the Promotion of Science, for their help and guidance in Mikura Island.

This study is a part of "Research Project on Conservation Methods of Subtropical Island Ecosystems" supported by the research promot- ing fund from the Environmental Agency of Japan, and also part of "Project on the Investiga- tion of the Nature of the Boso, Izu, Ogasawara and Mariana Archipelagos" supported by the grant of Natural History Museum and Institute, Chiba.

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