e the Russian wheat aphid, that attack crops; parasitic plants like witch weed, which now affect corn farmers; or weeds, such as thistles, that invade cropland. Alien weeds like spotted knapweed, star thistle and cheat grass reduce the quality of rangeland for grazing cattle, while fungi and insects plague both croplands and forest trees. A recent arrival is the Asian long-horned beetle, first detected only in the past three years, now feasting on hardwood trees in the Northeast.
"This beetle came over from China in wood packaging material and is destroying street trees in several cities in the East," she said. "It has a very wide host range and, while it is currently feasting on a variety of maple species, it has the potential to expand to many other types of trees."
Crop weeds accounted for $26 billion in loss and control last year, while agricultural pests cost the country $14.4 billion, according to the report in Bioscience. Forest pests, on the other hand, cost $2.1 billion, counting control costs and lost production. Fire ants alone accounted for a billion dollars last year in control costs and the loss of rangeland in the Southeast and Texas.
Apart from economic damage, however, these invaders upset the ecosystem, preying on native species, outcompeting them and spreading disease. They also can alter ecosystem processes to the point that the systems can no longer support native species. Non-indigenous species are second only to land use change in causing species extinction, D'Antonio said.
"I don't think any native communities are entirely resistant to invasion," she said. "With repeated introduction of new propagules, you increase the probability that a few of them will establish themselves, and eventually some will cause the extinction of native species."
Propagules are larvae, seeds or pieces of plants or fungi capable of developing into mature adults.
One of the major sources of alien pathogens such as fungi are nursery plPage: 1 2 3 4 Related biology news :1
Contact: Robert Sanders
University of California - Berkeley
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