Stanford, California
Of all species introductions in agriculture, 35% come from southwest Asia, 15% from southeast Asia, and 21% form South America. Crops are moved all over the world. Less than 1% of the world's cereals, starches, fruits and vegetables originated in North America, though it is now considered to be the breadbasket of the world.
Regarding intentional introductions, how can sensible risk analysis be performed to help avoid harmful invasions? A case study of a problem invasion is the golden apple snail in Asian rice systems.
The golden apple snail (Pomacea canaliculata) invasion provides important lessons for economists as more intentional and unintentional introductions can be anticipated under the Global Agreement on Tariffs and Trade (GATT) and the North American Free Trade Agreement (NAFTA). The golden apple snail was intentionally introduced from Argentina to Taiwan in 1981 as a potential food source and was subsequently introduced into other Asian countries. Pomacea snails were confirmed to have infested 34 of the 47 rice-growing districts in Japan by 1986, and in the Philippines, the proportion of wet-rice area infested by the golden apple snail rose from less than 3% in 1982 to as much as 15% by 1991. In China, Vietnam, Thailand, Malaysia, Indonesia, Taiwan, South Korea, Laos, and Papau New Guinea, the snail has already invaded several of the main rice growing areas.
The stakes of the golden apple snail invasion are very high because rice is the major food and employment source in Asia and yields are already plateauing. Another major problem that reduces yields could be devastating. Could we have predicted this kind of invasion and its impacts? It wasn't known that the snail would feed voraciously on young rice seedlings and would be dispersed through the extensive irrigation networks of rice-growing regions. The snail is now the #1 pest in the Philippines. This case points to the need to analyze and predict probability of invasion and probability of damage from invasion versus benefits involved in the medium term - 5 to 9 years in the future.
Naylor went through Sara Reichard's list of what makes a successful invader and applied those criteria to the snail. The characteristics that make the snail a successful invader are the same ones the entrepreneur looks for to maximize profits from introducing the snail as a potential food source (rapid reproduction, etc.). But the potential effects of the snail on the major food crop - rice - were not examined in advance. We now know that the damage has been enormous while the benefits have been very limited. There was no market testing prior to the introduction and once cultivation began, it was discovered that there was no market. European health restrictions limited the European export market, and the local Asian populations simply didn't like them.
The costs of the golden apple snail invasion in rice production includes the direct costs of controlling the snail, the costs of replanting (after initial destruction of seedlings by snails), and rice yield loss. The huge costs of replanting greatly reduces farmers profits. (See Tables 18.1 and 18.2 for details on financial costs.) Direct seeded rice is the most vulnerable to snail damage. Many new rice varieties are direct seeded, including the new "super rice" varieties that are expected to raise rice yields by 40% or more during the next decade, so the snail could become an even bigger problem.
In addition to the affects on rice yields, the golden apple snail has a direct impact on human health. The snail is an intermediate host of the lungworm,Angiostrongylus cantonensis, which is normally parasitic in rats, but which also causes the fatal disease eosinophilic meningoencephalitis in humans. Moreover, the snail acts as an intermediate host to various trematodes that cause skin irritations in humans.
The molluscicides and insecticides used for snail control are persistent organotins that are toxic to people and other species. Human health effects include nails falling out, skin problems, blurring vision, and blindness. There are also significant and long- lasting downstream effects on natural marine ecosystems. The types of chemicals generally used are persistent and accumulate in sediments. In addition, these chemical controls are not effective without good water control, and irrigation is not always well- controlled, especially in the monsoon season. Many of these chemicals have now been banned in Japan, Taiwan and the Philippines. There are currently no known chemicals which are safe, effective, and cheap enough for farmers to use.
Integrated snail management is being advocated, including hand picking of snails, herding ducks to eat smaller snails, better water control, spot pesticide treatment, and more seeding. However, results of the integrated approach do not reveal how effective each component is. Hand-picking is the most effective but also the most labor intensive. Ducks are effective but only during one part of the life cycle of the snail. And improving water control has proven very difficult.
Biological controls being considered or tried include raising common carp and Nile tilapia to eat snails, genetically manipulating snails to breed less rapidly, and botanical pesticides. Because botanical pesticides are biodegradable, it is believed that they are less likely than synthetic pesticides to leave harmful residues; however, they may also be toxic and cause resistance to build up in the pests over time. Another strategy is to try to get people to eat the snails by sending out brochures with snail recipes.
The extensive economic, ecological, and health ramifications of the golden apple snail invasion in Asia provide a perfect illustration of what Elton (1958) meant by "the piling up of new human difficulties." This invasion is clearly a case of an introduction that should not, and perhaps would not, have occurred if closer policy attention had been directed toward the full set of risks associated with it. It also raises the question of quarantine procedures, which are not very stringent in many industrialized countries, and noticeably absent in many developing countries where there is a lack of both training and regulation on species introductions.
Institutionalizing quarantine programs in developing countries that can effectively mitigate the introduction of exotic species is critical for two reasons: to reduce the scale of biodiversity loss and ecosystem damage globally, and to avoid large economic losses that poor countries and poor people can ill afford. Given that exotic species are vulnerable at the early stage of establishment, investments in programs to avert introductions or to eliminate early establishments have a much higher return than investments in control of well-established pests. For example, the resources spent by Philippine rice farmers on snail damage could have been better spent on implementing a viable quarantine program for all agricultural introductions.
Biological invasions in agriculture, as well as in largely natural systems, serve as yet another warning that ecological disruption, often severe and permanent, can be caused by human action that is driven by the desire for short-term economic gains. Bringing ecology into agricultural policy analysis thus deserves to become a high priority. Greater attention to ecological principles is needed, in particular, in assessing the risks of species invasions, in designing integrated pest management strategies, and in defining quarantine procedures. In additional, understanding economic factors that influence human behavior is critical in defining the ecological equilibrium of an agricultural system.
