Rooting out invasive species lessons from down under

Environmental Health Perspectives, July, 2007 by Tim Lougheed

In a world where heightened airport security is the norm, Australia and New Zealand might seem like a parallel universe. Dogs patrol airport aisles, sniffing not for illegal drugs, but for wayward fruits and vegetables. While the luggage of outgoing pas-sengers may be X-rayed for weapons, incoming visitors have their suitcases scanned for any kind of biological material. You can be required to surrender your shoes, not because they might contain explosives, but because you neglected to clean them off after hiking in some foreign rural area. The security in question is biosecurity--protection against incoming exotic species--and at these check-points, no packet of garden seed is too innocent to be seized.

Both countries have powerful incentives for such stringent enforcement. Although Australia and New Zealand are highly urbanized societies, their economies feature a significant agricultural sector that is exceptionally vulnerable to the ravages of invasive species. More recently, though, many observers are adding the prospect of human health issues to the toll exacted by exotics.

In fact, the gauntlet found at these countries' international air-ports is just the most obvious aspect of how seriously local authorities and scientists regard the issue of biosecurity. Government policies and academic institutions regularly adopt a unique focus on the way in which plants and animals cross national boundaries, a perspective that may look downright xenophobic at first glance.

Nevertheless, the experience of Australia and New Zealand can provide a valuable example to parts of the world that treat their boundaries in a more casual fashion, at least from a biological point of view. Accomplishments in these countries can offer important lessons to any country that must confront the combined impact of rising volumes of international trade and shifting climate patterns.

Worlds Apart

The lands Down Under are unique in having developed in physical isolation from other major land masses after splitting from the supercontinent of Gondwana tens of millions of years ago (estimates of just how long ago vary). Odd creatures such as the duck-billed platypus and the kangaroo serve as poster species for a remarkable evolutionary segregation, testifying to a path of biological development and survival well removed from the world's beaten paths. Flora and fauna in places like Europe, Asia, and the Americas long ago fought for and won ecological niches on their home turf, but some of those battles are just starting to be waged in the antipodes, with the relatively recent influx of exotic species.

When settlers began to colonize these outposts, they regularly spawned such battles by introducing plants or animals in a bid to make a sometimes strange landscape look more familiar to European eyes. The outcome was often devastating, perhaps never more so than following the release of a handful of rabbits in 1859 by an immigrant who wanted to hunt them on his Australian property as he had enjoyed doing in England. The comparatively mild Australian winters meant the rabbits could breed year-round; within a decade the animals had multiplied by the millions, munching on native plants--which had adapted slow growth patterns over millennia of exposure to Australia's drought-prone climate--and devastating an already parched topsoil. The result was serious erosion and agricultural damage that continues to this day.

Richard Roush, an American entomologist who is now dean of the University of Melbourne's Faculty of Land and Food Resources, can offer a long list of plants and animals that newcomers brought to the country to replicate their homelands' gardens, pastures, and livestock. He suggests that as many as half of Australia's problem species have arrived in this fashion, and that the trend has not waned until comparatively recently.

In research initiated in the early 1990s and published in the September 1994 issue of Austral Ecology, the Commonwealth Scientific and Industrial Research Organisation (the country's leading research body) surveyed instances of some 463 exotic grasses and legumes being deliberately planted in the country's north between 1947 and 1985. Of that total, 60 species (13%) eventually came to be listed as weeds, including most of the 21 species that also emerged as agriculturally beneficial. While many of the plants surveyed may have held aesthetic appeal for gardeners, only 4 out of the 463 attempts were identified as useful agricultural specimens with no weedy characteristics.

At about the same time this research was being conducted, Roush documented the arrival of the silverleaf whitefly (Bemisia spp.) into Australia. He was familiar with this pest's earlier incursion into California, where it had been transported with shipments of poinsettias. In Australia, Roush called for restrictions on imports of these same plants to forestall the problem, only to be told by Australian authorities that such quarantine efforts could be interpreted elsewhere as a trade barrier under the terms of the General Agreement on Tariffs and Trade. This international treaty sets forth rules for fair and free exchanges of goods between countries. Within a decade, in a March 2003 report titled Silverleaf Whitefly--Threats and Management Issues for Broad-Acre Crops in Eastern Australia, Richard Sequeira of the Queensland Department of Primary Industries wrote, "Silverleaf whitefly poses the latest and greatest pest threat to a wide range of agricultural crops in eastern Australia because of its wide host range, high reproduction rate, and its ability to rapidly develop resistance to insecticides."