Looking for Ways to Fight the Alien Invasion

SP-18: Stemming Invasions of Forest Insects and Pathogens: Research Supporting Pathway Risk Management and Phytosanitary Policy

Example of  pine wilting caused by pinewood nematodes. Credit: University of Illinois Extension
Example of pine wilting caused by pinewood nematodes. Credit: University of Illinois Extension

The principal pathway for invasive species to enter Europe is not through wood or logs, according to Alain Roques, but rather through the plants that people cultivate in their gardens and around their homes.

“The most likely pathway is the ornamental plant trade, which is responsible for the introduction of more alien species than are forest products,” he said. Roques is affiliated with the French National Institute for Agricultural Research.

Roques noted that there is a large difference between the families of plants that are affected by invasive species. “There has been a fast increase in Myrtaceae, Fabaceae, Rutaceae, Arecaceae, but a decrease in Pinaceae and Fagaceae. However, that does not mean that the latter ones are not affected,” he said.

Over time, a change has occurred between the origins of the invasive species. “Asia has become the dominant donor area, instead of North America, because if the steep increase in Asian imports,” he said.

According to Roques, there are three factors that make the European situation unique with regard to invasive species. First, he said, the fact that borders within Europe have been abolished allows a faster spread of invasive species. Second is the “bridgehead effect,” which occurs when one population of invasive species serves as the source for subsequent invasions elsewhere. Finally, the intra-European trade of large trees allows invasive species to jump over the front edge of the invasion and infest locations hundreds of kilometers away.

Alberto Santini, affiliated with the Institute of Plant Protection, discussed pathways for global forest pathogen invasion. According to Santini, 56 percent of emerging infective diseases are a result of introduced species. In particular he noted that we should be wary of fungi. “They are becoming an important agent of disease,” he said. “And not just in plants, but in animals as well, including humans.”

The main drivers of the increase in infective diseases are the arrivals of alien pests and pathogens, in particular after the end of World War II until the present, he said. Santini also noted the increase in hybrids that occurred between 1975 and 1999. This hybridization occurs between two species—one of which is a resident and the other which is the immigrant—and is dangerous because it can enlarge the range of the pathogen.

According to Santini, climate change can induce pathogens to an accelerated evolution or a migration to milder climates. He noted research that has shown that range of crop pests and pathogens are moving toward the poles as the world warms. In addition, Santini mentioned a few unexpected pathways for pathogen invasions, including cotton and denim clothing and the footwear of airline passengers.

Jianghua Sun, who is affiliated with the Institute of Zoology of the Chinese Academy of Sciences, discussed the current status of forest invasive pests in China, where a sizeable portion of the country is at risk. “Approximately 20.1 percent of China is forest-covered,” he said. “There are 2,958 forest pest control and quarantine stations, which include 1,000 national monitoring stations.”

“In China,’ he said, “Invasive species account for more than 50 percent of forest pest species. Both the number and the frequency of invasive species are increasing.” According to Sun, the damage caused by invasive species is rising. Economic loss is 57.4 billion RMB and will increase.

“Of the invasive species in China, 30 percent come from North America, 24 percent come from South America, and 17 percent come from Europe,” he said. Three of the top invasive species are pinewood nematodes, red turpentine beetles, and fall webworm. The nematode originated in North America but likely came to China via Japan. The beetle arrived with unprocessed logs from the United States. The webworm was introduced in China via packing containers from the United States.

Sun emphasized that in order to reduce impacts, international cooperation is required at every step of the invasion process, including risk assessments, monitoring and detection, and control.

Brian Leung, who is in the Department of Biology at McGill University, was the fourth presenter. Leung’s research dealt with the modeled impacts of implementing International Standards for Phytosanitary Measures No. 15, better known as ISPM15, which is a policy for treating wood packaging material.

Based on records of random cargo inspections before and after implementation of ISPM15, Leung found a 52 percent decrease in infestations. His analysis included an expected annual cost of U.S. $34 million per pest and an estimated initial ISPM15 cost of U.S. $437 million.

However, results indicated an expected net present value of U.S. $11.9 billion when accounting for costs and benefits through 2050. By 2016, annual benefits were projected to exceed annual costs. By 2025, the cumulative net present value is expected to be positive.

Written by: Pete Gomben

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