Kagoshima University Research Center for the Pacific Islands Occasional Papers No.39, 73-75, 2003
Section 2, Report 7. The Progress Report of the 2000 and 2001 Survey of the Research Project“Social Homeostasis of Small Islands in an Island-zone”

73THE BIOGEOGRAPHY OF THE INSECT FAUNA OF THE ULITHIISLANDS, MICRONESIATSUDA Katsuo＊ , WATANABE Masao＊ , TOMINAGA Shigeto＊, ONJO Michio ＊, andICHITANI Katsuyuki＊

Abstract
Ulithi Atoll in Yap State is located in the western zone of the Federated States of Micronesia andcomprises 49 islets. In a survey of Ulithi Atoll, we visited its four inhabited islands, Asor, Falalop,Fassarai, and Mogmog. Insects were collected both by day and night, and 262 species of insects fromnine orders were recorded. In order to estimate the species richness and natural environment of eachisland, the number of species in each taxonomic order was considered. Fassarai had the greatest species richness of the four islands, while Mogmog had the least. This suggests that human inhabitation
affects insect species richness, because most of Mogmog Island was used as living space.
Keywords: island, insect fauna, Micronesia, species richness, Ulithi

Introduction
The Ulithi Islands consist of 49 small islets, situated in the northeast part of Yap State.
Presently, Asor, Falalop, Fassarai, and Mogmog Islands are inhabited. Ulithi has a tropical climate, with relatively even, warm temperatures year-round. Rainfall is generally plentiful, but
droughts occur periodically. Tropical typhoons are an annual threat to the low-lying atolls. All
the islands except the low atolls are forested, and this consists of an agro-forestry complex withscattered secondary forest.
During the Yap Research Expedition in 2001, conducted by Kagoshima University
Research Center for the Pacific Islands, we had the opportunity to survey the insect fauna of theUlithi Islands. The insect fauna and the differences between islands might have played an important role in the culture and history of each island. In order to compare the insect faunae, we collected insects on four inhabited islands: Asor, Falalop, Fassarai, and Mogmog. There are few
previous collecting records for the islands, although there are some records of the insect faunaof Yap proper. Insect pests were surveyed by the College of Micronesia (N ELSON et al. 1990)
and by a previous expedition from Kagoshima University (SAKAMAKI et al. 2001). Insect inventories can provide a tremendous amount of information about natural systems because insects respond to environmental changes quickly. Insects are often a key component of terrestrial
ecosystems. The spatial distribution of an insect species is the result of both behavioral and environmental factors (TAYLOR 1984; N ESTEL et al. 1995).
This study considered the social homeostasis of four islands in Ulithi Atoll from abiogeographical perspective.

＊Faculty of Agriculture, Kagoshima University. Kagoshima 890-0065, Japan.

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TSUDA Katsuo, WATANABE Masao, TOMINAGA Shigeto, ONJO Michio, and I CHITANI Katsuyuki

Materials and Methods
This survey was carried out on Ulithi Atoll from 20 to 25 October 2001. Insects were collected on four islands: Falalop (20 and 21 October), Asor (21 October), Fassarai (24 October),and Mogmog (23 and 25 October). The islands cover 90, 67, 48, and 27 ha, respectively. All fourislands are equally flat, and the highest point on these islands is 11.6 m on Falalop Island. Usinginsect nets, insects were collected during the day from grassy areas, bushes near the beach, forestgaps, around forest edges, and in forests consisting of various tree species. Insects were also collected for one night on each island by light trapping. We attempted to classify all the insects collected during the survey at the species level, although some specimens could not be identified as
to species.

Results and Discussion
One of the main difficulties with this study is how to evaluate the intensity of the surveys.
Survey intensity is determined by factors such as the number of collectors, their skill and experience, the total time devoted to collection, and weather. Another difficulty is the reliance to beplaced on absences. A species may be erroneously recorded as absent when collecting has been
insufficient or in the wrong season, or when a species is rare. This survey was limited, in thatsamples were collected on only one or two days per island. This might be insufficient to estimate
the ecosystems of each island. Fortunately, the conditions during the surveys were almost identical on each island. Unfortunately, optimal sampling schemes have not been developed for estimating biodiversity. LANDAU et al. (1999) compared two methods of sampling in moths andfound a high similarity between intensive and long-term collections. This implies that we can estimate species richness from short-term collections.
In general, islands contain fewer species than comparable mainland areas (BEGON et al.
1990). In the survey, we collected more than 300 insect species, from nine orders. Insects wereeasily identified as to order, although it was very difficult to identify some as to species. In orderto estimate species richness, we determined the number of species in each order for each island(Table 1). M ACARTHUR and WILSON (1967) pointed out that the number of species on a given
island is usually approximately related to the area of the island. In our survey, no correlation witharea was observed, implying that the differences in area were too small to influence the results.
The details of the insect fauna on each island are as follows:
Table 1. The number of insect species collected in the Ulithi Islands
Order
Asor
Falalop＊
Lepidoptera
2415
Coleoptera
1217
Hymenoptera
1214
Diptera3034Hemiptera
921Orthoptera
411Odonata
35
Dermaptera
11Blattaria
00Total95118＊Some species were not identified.

Fassarai
163412371710230131

Mogmog27158236541291

Total
6247
2963
31
16662262

THE BIOGEOGRAPHY OF THE INSECT FAUNA OF THE ULITHI ISLANDS, MICRONESIA751) Asor Island
Only 40 people inhabit Asor Island. It is mainly forest, with a small grassy area. The number of species collected on this island was greater than predicted, most likely as a result of thespecies richness conserved by the forest.
2) Falalop Island
Falalop Island is the largest and most populated of the four islands. The airstrip, radio transmitter, administrative offices, post office, and Outer Islands High School are all on Falalop
Island. It is mainly forested, but there are some grassy areas near the airstrip and high school. Wecaught relatively large numbers of hemipteran and orthopteran species. Most of these seemed toprefer grassy areas. In contrast, fewer lepidopterans were caught than expected, likely as a resultof the location of the light trap and the rainfall at night.
3) Fassarai Island
Fassarai Island is approximately 20 and 24 km distant from Asor and Mogmog, respectively. It is a long, narrow island, about 3.0 km long and 100 to 200 m wide. It is mainly forested,with some grassy areas. Fassarai had the greatest species richness among the four islands. We
caught more coleopterans here than on the other islands, and most were specific to this island.
4) Mogmog Island
Mogmog is the second most populated island of Ulithi, with 165 inhabitants, and is also thesmallest of the four islands. It is also forested, but most of the island is used as living space. Inthe survey, Mogmog had the fewest species. This implies that the human population has had
some effect on the richness of insect species.
Finally, we thank Dr. SAKAMAKI Yositaka (Lepidoptera), Dr. Y AMANE Seiki(Hymenoptera), and Mr. K AGESAWA Nobuhiko (Diptera) of Kagoshima University, Mr.
M AKIHARA Hiroshi (Coleoptera) of the Forestry and Forest Products Research Institute, andK ARUBE Haruki (Odonata) of Kanagawa Prefectural Museum of Natural History, for identifying
some of the insect specimens collected during the survey.

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