文章来源:未知 文章作者:enread 发布时间:2017-06-04 06:54 字体: [ ]  进入论坛
Swarms1 of cicadas are unexpectedly crawling out from under trees from North Carolina to New Jersey2. The red-eyed insects are almost impossible to miss; they fly around lazily, plunking into backyard barbeques and crashing into cars. They litter the ground with their crunchy husks as they molt3. Most noticeably, they chirp4 en masse for their mates, producing a relentless5, shrill6 buzz that is recognized as a song of summer. And within a month they are gone.
Different populations, or broods, of "periodical" cicadas emerge in distinct geographical7 regions during specific years, after spending a 13- or 17-year span growing underground. (Some "annual" species just emerge yearly.) Scientists were expecting to see Brood VI bugs8 in South Carolina and Georgia, which happened, but they got a surprise when Brood X cicadas also started appearing in North Carolina, Virginia, Maryland, the District of Columbia, Ohio and Indiana last week -- four years earlier than anticipated.
Experts suspect a warming climate, with more warm weeks a year during which the underground nymphs can grow, could be triggering some cicadas to emerge ahead of their brood. "Temperature is everything," says Marlene Zuk, an entomologist at the University of Minnesota. "When temperature changes, insects don't just feel hot or cold. Their whole body doesn't function normally." And cicada nymphs may be growing to a threshold size so quickly that their internal biological clock is miscalculating when it is time to emerge, says Keith Clay, a biologist and cicada expert at Indiana University Bloomington. To calibrate9 these clocks, periodical cicadas likely rely on a variety of environmental cues such as changing seasons and ground temperature, he says. Nymphs feed on the xylem fluid (sap) from tree roots, and changes in the fluid composition as trees leaf out each spring may also help them gauge10 the passage of time. Entomologists reached this conclusion back in 2000 when they artificially sped up the blooming cycle of peach trees supporting cicada nymphs that were in their 15th year and tricked the insects into emerging a year early.


1 swarms 73349eba464af74f8ce6c65b07a6114c     
蜂群,一大群( swarm的名词复数 )
  1. They came to town in swarms. 他们蜂拥来到城里。
  2. On June the first there were swarms of children playing in the park. 6月1日那一天,这个公园里有一群群的孩子玩耍。
2 jersey Lp5zzo     
  1. He wears a cotton jersey when he plays football.他穿运动衫踢足球。
  2. They were dressed alike in blue jersey and knickers.他们穿着一致,都是蓝色的运动衫和灯笼短裤。
3 molt Rj9yb     
  1. The fourth time they molt,they change into pupae.换第四次皮时,它们蜕变成蛹。
  2. This veterinary product is very effective in preventing animal molt.这种兽药对于防治兽类掉毛很有效。
4 chirp MrezT     
  1. The birds chirp merrily at the top of tree.鸟儿在枝头欢快地啾啾鸣唱。
  2. The sparrows chirp outside the window every morning.麻雀每天清晨在窗外嘁嘁喳喳地叫。
5 relentless VBjzv     
  1. The traffic noise is relentless.交通车辆的噪音一刻也不停止。
  2. Their training has to be relentless.他们的训练必须是无情的。
6 shrill EEize     
  1. Whistles began to shrill outside the barn.哨声开始在谷仓外面尖叫。
  2. The shrill ringing of a bell broke up the card game on the cutter.刺耳的铃声打散了小汽艇的牌局。
7 geographical Cgjxb     
  1. The current survey will have a wider geographical spread.当前的调查将在更广泛的地域范围內进行。
  2. These birds have a wide geographical distribution.这些鸟的地理分布很广。
8 bugs e3255bae220613022d67e26d2e4fa689     
adj.疯狂的,发疯的n.窃听器( bug的名词复数 );病菌;虫子;[计算机](制作软件程序所产生的意料不到的)错误
  1. All programs have bugs and need endless refinement. 所有的程序都有漏洞,都需要不断改进。 来自《简明英汉词典》
  2. The sacks of rice were swarming with bugs. 一袋袋的米里长满了虫子。 来自《简明英汉词典》
9 calibrate vTvyu     
  1. Pesticide levels in food are simply too difficult to calibrate.食品中杀虫剂的含量很难精确测定。
10 gauge 2gMxz     
  1. Can you gauge what her reaction is likely to be?你能揣测她的反应可能是什么吗?
  2. It's difficult to gauge one's character.要判断一个人的品格是很困难的。
TAG标签: insects trees cicadas