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Sunday, Sept. 30, 2001

Alien invaders

Special to The Japan Times

They arrive in bunches of bananas; they turn up in containers of vegetables; they sneak in hidden inside rattan and wooden furniture; they disembark from among shipped household possessions, industrial and military equipment. They are as pervasive as the computer server virus Nimda, but, in their own way, far more destructive.

What are they? Not illegal immigrants but aliens nonetheless -- and seemingly Japan has no laws for restricting either their arrival or their dispersal.

These aliens are capable of withstanding chilling; gassing; changes of pressure; and lack of both water and food for prolonged periods. They are the most successful living creatures on Earth: They are insects.

Alien or introduced species, those "imported" from outside their natural range into a country unaccustomed and ill-equipped to cope with them, perhaps represent the greatest environmental threat after habitat loss. Accidental introductions are problematic enough, but the deliberate introduction of species is tantamount to ecoterrorism, with potentially catastrophic results.

Introduced mammals, birds, fish, reptiles and amphibians can wreak havoc with ecosystems in a delicate equilibrium, but at least the larger of them are noticeable: black bass in Lake Biwa, mongooses in the Nansei Shoto, raccoon in Hokkaido. But who notices alien insects? Who, even, can identify them?

Japan's insect biodiversity is so great that there are few specialists capable of recognizing the new invaders. Discovery of a new species poses a conundrum: Is the creature a native species merely overlooked in the past, or a newly arrived alien? Only investigations by experts in a particular taxonomic field may provide the answer.

But how grave is the problem? One moth here, a mosquito there, the odd beetle or spider -- do they really matter?

For many species, one egg-laden female is all it takes to launch a new population of potential agricultural, forestry or social pests. Surely, the arrival of the western large bumblebee in Hokkaido can't be a problem?

Wrong. A competitor for nectar, it is displacing local bumblebees that ultimately lose out in the competition for survival. Not having co-evolved with native flowers, the differently proportioned mouthparts of the invaders enable them to take the plants' nectar without providing that most crucial of services, pollination, in return. As their rates of pollination decline, so too does the reproductive success of the plants; gradually they will lose ground and become extinct in turn.

Introduced beetles can play havoc with natural forest cover and forest industries, as has been discovered to considerable cost in the United States and Britain. Introduced bee mites can devastate honey industries (as in the North Island of New Zealand). Alien ants, such as the South American fire ant that has reached the Galapagos Islands and Australia, not merely descend on native insects, reptiles and even birds, but force people to change their behavior. The great Aussie barefoot barbecue in the yard and children playing shoeless or in sandals in the park may become pleasures of the past if the fire ant, with its excruciating bite, is not eradicated quickly.

And lest you think "it couldn't happen here," one of the fire ant species, the Argentine ant Linepithema humile, has already made it to Japan. It was discovered in 1993 in residential areas of Hatsukaichi City, Hiroshima Prefecture. Be careful where you tread.

The range of alien creepy-crawlies already found in Japan is wide. No doubt because of the extent of trade between the two countries, many of them originated in the U.S. They threaten pine forests (the pine wood nematode, Bursaphelenchus lignicolus, introduced as early as 1905), cherry trees (the fall webworm, Hyphantria cunea, a 1945 arrival, is a serious defoliator of such trees) -- and even rice crops (the rice water weevil, Lissorhoptrus oryzophilus, introduced in 1976).

Lax controls at customs, airports and container ports have allowed a wide range of aliens to enter Japan, where the general level of public awareness about the dangers of alien species is woefully low.

Not only might that accidental invertebrate devastate a fruit crop, a tree harvest or out-compete a native species, it might even threaten people. Mention poisonous spiders, and many people will at least know of the infamous American black widow with its potentially lethal bite. A close relative of the widow (although not as deadly) is the Australian red-back spider, first reported here in November 1995 at Takaishi, a port city in southern Osaka Prefecture.

Both infestations occurred at, or near, ports receiving imports from Australia, where the red-back is both common and widespread. When the related Australian brown widow was found to have reached Okinawa on Dec. 7, 1995, however, the discovery complicated our understanding of the invasion routes of these spiders. Okinawa is not a major port and receives few Australian goods. The spider's means of arrival remains a mystery.

Japan is by no means the first country to be colonized by alien spiders. Red-backs have reached New Zealand and, more amazingly, the remote South Atlantic island of Tristan da Cunha. They are thought to have reached the latter thanks to a satellite-station tracking unit that was airlifted from western New South Wales to Florida, where it was stored for three weeks before being shipped to Tristan da Cunha.

But these examples are just the tip of the iceberg: No fewer than 300 alien insect species have become established in Japan since 1868. While not a new phenomenon, alien insects are increasingly a force to be reckoned with; they may bring pain, economic hardship or carry diseases affecting crops -- or us. That is no reason to wage war on all insects, but it is certainly justification for stepping up control measures at customs and immigration, and for encouraging the teaching of insect taxonomy the better to safeguard Japan's bio-integrity.

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