美国东部玉米螟虫的数量显著下降

Populations of European corn borer（玉米螟） (ECB), a major corn crop pest , have declined significantly in the eastern United States, according to Penn State researchers. The decline suggests that the use of genetically¹ modified, ECB-resistant corn hybrids² -- an expensive, yet effective, solution that has been widely adopted by farmers -- may now be unnecessary in some areas. "ECB, which was introduced to North America from Europe in the 1900s, used to be the most important pest of corn in the United States," said John Tooker, assistant professor of entomology（昆虫学）. "Not that long ago, it caused crop losses that annually³ approached $1 billion nationwide, and $35 million in the northeastern United States."   According to Tooker, to protect their crops from ECB, many farmers have grown a genetically modified type of corn that expresses insecticidal toxins⁴ that kill the worms. These toxins were isolated⁵ from the bacterium⁶ Bacillus thuringiensis (Bt).   "These Bt corn hybrids have been widely adopted because they are exceptional for managing ECB -- 99.9 percent of larvae⁷ are expected to die when they feed on plants expressing Bt toxins," he said. "Yet a drawback to using these hybrids has been the high cost of purchasing the seeds, which can decrease potential profits."   To understand current ECB populations in Pennsylvania field corn, the researchers assessed larval damage in Bt and non-Bt corn hybrids at 29 sites over three years. Specifically, they planted Bt and non-Bt corn hybrids on farm sites across four growing zones in Pennsylvania in 2010, 2011 and 2012. During September of each season, they assessed corn borer damage on 400 random⁸ plants at each site. They sliced open stalks, and recorded the number of ECB tunnels and larvae（幼虫） per stalk. They also evaluated corn ears for ECB damage.   "Our results confirm that we are seeing widespread population declines of ECB in the East, similar to declines that have been found in the Midwestern United States," said Eric Bohnenblust, graduate student in entomology. "With less ECB damage around, non-Bt hybrids in our tests yielded just as well as Bt hybrids, so the decline in ECB populations provides an opportunity for growers to generate greater profits by planting high-yielding non-Bt seed, which is much cheaper than Bt seed. Secondarily, planting more non-Bt corn will reduce the potential for ECB to develop resistance to Bt toxins as corn rootworms have done in about a dozen states so far."   The team's results appeared in an early online edition of the journal Pest Management Science in December.#p#分页标题#e#