The Threat of Invasive Pests Grows With Global Trade

An adult Asian citrus psyllid feeds on the new growth of a citrus tree. These invasive pests have already severely impacted the citrus industry in Florida, and are now spreading to other parts of the United States. CDFA/Handout/Reueters

A moth with a voracious appetite for tomatoes made its way from its native South America across the Atlantic to Spain in 2006, before setting its infinitesimal foot in the Middle East and then recently Africa. The female tomato leaf miner lays a couple of hundred eggs that stick to the underside of tomato plant leaves before hatching into larvae that bore through every last part of the plant, destroying it and making fruits pockmarked and inedible. This is not such a big deal for backyard gardeners, but it is a huge problem for tomato farms, where the moth's larvae have reduced crop yield by 80 to 100 percent in some places.

Though invasive pests like this moth don't really care where they proliferate, as long as their preferred host plant is in abundance, a new study published in the Proceedings of the Academy of Sciences shows that they are likely to have a much bigger effect on developing countries than on wealthier ones.

Researchers led by Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) examined the difference in the effect invasive pests and pathogens have on 124 different countries. The research identified countries most vulnerable to invasive pests—all in sub-Saharan Africa—as well as countries that pose the greatest threat as a source of invasive species—the United States and China. This is not surprising, given the high number of invasive species already present in those countries, the size and scale of their agricultural industries and their role as regional food hubs, according to Dean Paini, senior research scientist and lead author of the study.

Invasive insects like the Asian citrus psyllid, which is crippling Florida's citrus industry, or the European grapevine moth, which plagues vineyards, have been said to cost the U.S. as much as $40 billion a year in crop losses and forest damage. As high-volume, round-the-clock global trade continues to be the norm, countries worldwide are under more pressure to respond to the effect of invasive pests.

CSIRO set out to quantify the threats by pinpointing the sources of potential pests and estimating their likelihood of entering a particular country. They started by identifying the main crops in 124 countries and noting whether those plants were a known host of one of 1,300 pests or pathogens of concern. If a particular country grew a host plant and its associated pest or pathogen was not already present there, the team then estimated the likelihood that it would enter the country via trade partners. The team then calculated the potential cost of the pest or pathogen on each crop.

The study found that 40 of the 124 countries studied were likely to be invaded by a pest or pathogen posing a significant threat to agriculture that had not already crossed their borders. Large agricultural producers such as the U.S., China, India and Brazil are predicted to suffer the most profit-wise, but they are also likely to be able to offset some of those losses, given the means they have to address the effect of invasive species. In addition, in many places where the threat of invasion is high, such as the U.S. and Scandinavian countries, agriculture is a relatively small contributor to overall gross domestic product. Therefore, invasive pests—while detrimental—will not be as devastating as they will be in the developing world, where economies rely heavily on agriculture.

The research revealed more about the complex relationship between the types of crops grown in the countries studied, the level of trade with other countries and the particular invasive species present in those countries. Italy, for example, imports twice the value of goods than Switzerland and Austria, but Italy is less at risk of invasion because fewer invasive species are established in the countries with which Italy trades.

To date, invasive species management and prevention has been left mostly to individual countries or regions. Paini's team believes their findings could help scientists and policymakers across the world collaborate on global solutions to prevent the spread of invasive pests. "This research provides insights that will enable the first steps towards the management of invasive species at the global scale," Paini said in a press release. "By identifying the countries and regions that are most vulnerable, governments can make informed decisions regarding the deployment of resources necessary to protect their borders and agriculture industries by limiting the further spread of invasive species."