Kagoshima University Research Center for the Pacific Islands, Occasional Papers No.34, 101-104, 2001
Part 1, Section 3, Report 3. The Progress Report of the 1999 Survey of the Research Project“Social Homeostasis of Small Islands in an Island-zone”

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SUSTAINING AGRICULTURAL PRODUCTION IN YAP:
AN ASSESSMENT OF PEST INSECTS AND PLANT DISEASE
Yositaka SAKAMAKI, Michio ONJO, and Satoru TAURA

Abstract
In a survey of Yap Island, we found that the ratio of broad-distributed pests is so high, more than70%. Those pests, which were imported or invaded from other area, have a great opportunity to beprevalent on Yap, because of a “poor-enemy” environment brought about by the isolation of the smallisland. We also found damaged taro in many villages. The agent causing the damage was not a nematode, but was probably a root-rot disease.
Sustaining healthy agriculture, the Yapese need to make the most of advantages of traditional
small-scale forest farming and strictly prevent inadvertent import of pests.
Key words: broad-distributed pests, isolation in small islands, taro, nematode, Yap

Pest Insects in Yap Island
Once upon a time most Yap proper people consumed mainly Taro, Yam, and Banana as
chief starchy food resources, while today young Yapese tend to prefer rice, ramen noodle andbread to local foods. The Yap diet has changed for decades, as many new foods and crops areimported or cultivated. And with these new foods and crops in Yap, many pest insects have also
been imported.
In general, islands contain fewer species than apparently comparable mainland areas.
(BEGON et al, 1990). This trend is observed also in the insect fauna of Yap Island. During oursurvey, we found significantly fewer insects in Yap than in Japan. (In Japan we typically get
more than 100 species of moths with light trapping in one night, for example, while in Yap wecollected fewer than 50 species in a two weeks visit.) However, the ratio of broad-distributed
insect species is higher in Yap than in Japan more than 70%. These broad-distributed species
have been able to fly from other islands, or to invade by riding on crops imported over the last
several decades. In the survey, we visited many farms in various villages of the island. Table
1 lists the pest species which were collected during our two weeks survey. A total of 23 pests
found attacking crops is enumerated. Seventeen species of them are broad-distributed species(cosmopolitan, Asian-Pacific or invading from the Americas). According to the lists in N ELSON
et al. (1990) and N AFUS & S CHTEINER (1999), about 70 species of 91 known pest insects in Yap
Island are broad-distributed species, which originated from another locality. Thus, over the lastfew decades many new pest insects have been invading and colonizing Yap, as transport of people, commodities and crops has increased, while Yap’s defenses, the fauna of natural enemies
and insects antagonistic to such pests, is poor because Yap is a such small island.
During our survey, we also researched the Yapese fauna of some natural pest insect enemies. We found only three species attacking pest insects (Table 2). We can infer that the listof natural enemies is poor, because it correlates with essentially poor insect fauna generally inYositaka SAKAMAKI et al.

102

Table 1. Pests found in the integrated survey in Yap Island (from 20, October to 2 November, 1999)
Name of pest

Crops attacked

Distribution

Japanese grasshopper, Oxya japonica (THUNBERG)
Sugar cane
Asian-pacificMigratory locust, Locusta migratoria manilensis (MEYEN) Sugar cane
Pan-tropicalOrange cucumber beetle, Aulacophora similis (OLIVIER) Cucurbits (cucumber,N. America & Pacificpumpkin etc.)
Sweetpotato weevil, Cylas formicarius (FABRICIUS) Sweet potato
Asian-pacific
Cowpea aphid, Aphis craccivora KOCH
Cow pea
Cosmopolitan
Cotton or melon aphid, Aphis gossypii GLOVERCucumber
Cosmopolitan
Taro leafhopper, Tarophagus proserpina KIRKALDY TaroPacificDiaspidid scale, Diaspididae Gen. sp.
Taro (mainly Cyrtosmerma)
Mealybug, Pseudococcus macrocirulus BEARDSLEY TaroPacific
Striped mealybug, Ferrisia virgata (COCKERELL)
Cockscomb, cucurbits,
Pan-tropicalsolanaceous crops etc.
Black island stink bug, Brachyplatys insularis (RUCKES) Cowpea
Asian-pacificLeaf-footed plant bug, Leptoglossus australis (FABRICIUS) Cucumber
Asian-pacific
Red stainer bug, ＊ Dysdercus cingulatus (FABRICIUS ) Okura
Asian-pacificBean bag, Riptortus clavatus (THUNBERG)
CowpeaAsian-pacificBagworm, Psyche sp.
Taro (mainly Cyrtosmerma) New to Yap Is.
Cosmopterigid moth, Cosmopterix sp. (leaf miner)
Sugar cane
New to Yap Is.
Sweet Potato Leaf Miner, Bedellia somnulentella ZELLER Sweet potato
Cosmopolitan
Gelechiid moth, Gelechiidae Gen. sp. (leaf miner)
Yam
New to Yap Is.
Sweet potato hawk moth, Agrius convolvuli (LINNAEUS ) Sweet potato
Cosmopolitan
Rice cut worm, Spodoptera litura (FABRICIUS )Chinese Cabbage
Asian-pacific
Lawn armyworm, Spodoptera mauritia GUENÉE
CornN. America & PacificSpotted bollworm, Earsia vittella (LINNAEUS)
Okra
Pan-tropicalSlug, Eleutherocaulis alte
Chinese Cabbage
Asian-pacific＊ In NELSON et al. (1990), this species is misidentified as Oxycarenus bicolor FIEBER of Lygaeidae.

Table 2. Natural enemies found in the integrated survey in Yap Is. (20, October to 2 November, 1999)
Enemy insects
hover fly (Syrphidae Gen. sp.)brown lacewing (Hemerobiidae Gen. sp.)
Pteromarid wasp (Pteromaridae Gen. sp.)

HostAphis gossypii on cucumber
Aphis gossypii on cucumber
Diaspidid scale on swamp taro

the environment of Yap Island. In such a “poor-enemy” environment, broad distributed invading
pests have a great chance to prevail.

Do Nematodes Really Attack Ginat Swamp Taro in Yap?
Present day Yapese are beginning to have a better opinion of traditional local foods.
However, we found giant swamp taro (Cyrtosperma sp.) frequently damaged by a disease, whichpoured cold water on such a better opinion. The symptoms were:-dwarfism, rotting roots andslow death of above ground parts. Infected plants were not densely concentrate, but were foundin the most of patches we visited. Some informants told us that the disease might be caused bynematode attack, so we tried to isolate nematodes from swamp taro roots collected in various
taro patches (Towoway village in Gilman, Runuw village in Fanif) by the Baerman funnel

Sustaining Agricultural Production in Yap: An Assessment of Pest Insects and Plant Disease103

method. The nematodes isolated were sent to the National Institute of Agro-Environmental
Science, Japan, and were identified as a species of non-phytophagous free-living nematode belonging to the family Cephalobidae (Fig. 1). In general, the Cephalobid nematode is an inhabitant of soil with decaying plant material, and it apparently feeds on the products ofdecomposition, including associated bacteria and perhaps other microorganisms (THORNE,1961). It was the only nematode species isolated. Consequently, we concluded that the agent
damaging giant swamp taro in Yap was not this nematode, and then we should look for anotheragent.
The detailed symptoms we observed were developmental delay, plants stunted, and outerleaves wilting and dying prematurely on older established plants. Leaf symptoms included crinkled leaf blades, and remaining leaves slightly rolled or curled inwards. The roots of damaged
plants had the following characteristcs: - decayed and healthy root tissue of root separated by a
sharp boundary; nematodes contributing to the developing disease; only a fringe of healthy root
remaining at the top of the corm as disease proceeded, and root interior transformed into a foulsmelling soft mass. These matched the characteristics of a kind of root rot disease caused by afungus belonging to the genus Phythium. Giant swamp taro, however, is resistant to Phythium
rot disease as far as we know (ADAP PROJECT, 1995). To precisely identify the agent of disease
we need to collect additional samples of damaged taro root.

Fig.1. The Cephalobid nematode isolated from the root of giant swamp taro planted in Yap Island(scale: 0.1mm).

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Yositaka SAKAMAKI et al.

The Way to Sustain Healthy Agriculture in Yap
Agriculture in tropical islands generally was small-scaled farming originally. Such farms
were located in forest, which could prevent rich soil from washing away and people planted traditional crops well fitted to small scale farming. The traditional way of farming in small-scaled
forest patches sustained a complex web of ecosystems, that is, adaptable living-communities
with numerous prey and numerous predators, and thus a high ability to restore ecological relationships even if they collapsed temporarily under pressure of invading prevalent pests. The forest buffer may also have prevented the invasion of prevalent pests such as the firewall. In
present day Yap, some of the new crops originated in Temperate areas (other Asian countries andNorth America) and farming styles have gradually changed to those where people utilize large
open fields. Such a farming style is economically efficient in a short-term view, but it is doubtful that it will continue being efficient in the long view. It tends to make the ecological web simple, and this must affect distinctly isolated islands like Yap which naturally have rather poor
insect fauna. Consequently, there is a high possibility that intensely prevalent pests with cosmopolitan distribution will colonize and severely attack some of the new temperate crops.
The Division of Agriculture and Forestry in Yap State strongly restricts the import ofchemical insecticides, because these chemical control agents have so many disadvantages: - danger to the user and to others, possible contamination of the farm, killing of beneficial insects, andincreasing farm costs, for instance. To sustain healthy agriculture in Yap from the point of viewof pest and disease controls, it is necessary to exploit the advantages of traditional small-scale
farming in a forest location. These advantages include the possibility of usisng modern“IPM”, cultural and biological controls. But Yapese needs to strictly prevent pest invasion via
the transporting of people, commodities and new crops into Yap.
Finally we wish to express our sincere thanks to Dr. T. M IZUKUBO, National Institute ofAgro-Environmental Science for identification of the nematodes.

References Cited
ADAP P ROJECT 1995. Phythium Rot of Taro in Pacific Islands Farm Manual [on line]. Hawaii,
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BEGON, M., H ARPER, J. L. and TOWNSEND, C. R. 1990. Ecology -Individuals, Populations andCommunities-. 2nd ed. xii+945 pp. Blackwell Science, Boston.
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N ELSON, M. E., JACKSON, A. P. and WILLIAM, S. W. 1990. Survey of pests of crops in theFederated States of Micronesia (Entomology portion). Extension Report 1. 58pp. Collegeof Micronesia, Land Grantprogram. Kolonia, Pohnpei.
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