AGRICULTURE REPORT - Sweet Deal: How Plants Invite Helpful I

AGRICULTURE REPORT - Sweet Deal: How Plants Invite Helpful Insects to Dine¹ on Harmful Ones
By Bob Bowen

Broadcast: Tuesday, November 08, 2005

I'm Shep O'Neal with the VOA Special English Agriculture Report.

Students are taught at an early age about how insects help plants reproduce². Schoolchildren learn that plants release sweet juices, or nectar, through small openings inside the flower. These small openings are called nectaries.

 
The sweet-smelling nectar appeals to bees and other insects so they go to the plant. While the bee is drinking the sweet nectar, the hairs on its legs become covered with pollen³. The bee flies to another flower and drops some of the pollen there.

During a flight, the bee usually visits several male and several female flowers. In this way, flowers are able to reproduce.

Many plants, however, release nectar for another purpose. Scientists have known about it for more than one hundred years.

The second way plants release nectar does not involve flowers. The nectar is contained in extrafloral nectaries. They are found on the tops of leaves, where the leaf and stem⁴ come together.

Trees that have extrafloral nectaries include the peach, poplar, viburnum, black locust⁵ and wild cherry.

Extrafloral nectaries are often smaller than a grain of salt. Researchers say the sweet juices released in them are not used to help the plant reproduce. Instead, they are used to get some insects to come to the plant to help control harmful insects.

Scientists have known for many years that tiny ants feed on the sweet juices released by the extrafloral nectaries. But only in more recent years did they make discoveries involving other insects.

Back in nineteen ninety-four there was a report about extrafloral nectaries in Agricultural Research magazine. The magazine is published by the United States Agriculture Department. It said two government scientists, Robert Pemberton and Jang-hoon Lee, had studied extrafloral nectaries for two years. They looked for ways to control gypsy moths⁶.

They did their research in forests near the South Korean capital, Seoul. During their research, they discovered that two helpful insects liked the extrafloral nectaries.

In fact, the insects killed two times more gypsy moths on trees that had the extrafloral nectaries than on those that did not. The insects are the Cotesia melanoscelus wasp⁷ and the Parasetigena silvestris fly.

A third insect, the Blepharipa schineri fly, also improved its control of gypsy moths on trees with extrafloral nectaries.

This VOA Special English Agriculture Report was written by Bob Bowen.  I'm Steve Ember.

1 dine   

vi.吃饭，进餐；vt.宴请

参考例句：

• I wish I could afford to dine off fresh meat every day.我要是能天天吃到新鲜的肉就好了。
• Let's dine out tonight，I'm too tired to cook.我太累了，不想做饭，今晚咱们到外面吃吧。

2 reproduce   

v.生育，繁殖，复制，重做

参考例句：

• The machine can reproduce a key in two minutes.这机器能在两分钟内复制一把钥匙。
• The picture will reproduce well.这照片会印得很清楚。

3 pollen   

n.[植]花粉

参考例句：

• Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。
• He developed an allergy to pollen.他对花粉过敏。

4 stem   

n.茎，干，船首，词干，血统；vt.堵住，阻止，抽去梗；vi.起源于，发生

参考例句：

• Cut the stem cleanly,just beneath a leaf joint.把茎切整齐点，正好切在叶根下。
• The ship was in a blaze from stem to stern.整艘船从头到尾都着火了。

5 locust   

n.蝗虫；洋槐，刺槐

参考例句：

• A locust is a kind of destructive insect.蝗虫是一种害虫。
• This illustration shows a vertical section through the locust.本图所示为蝗虫的纵剖面。

6 moths   

n.蛾( moth的名词复数 )

参考例句：

• The moths have eaten holes in my wool coat. 蛀虫将我的羊毛衫蛀蚀了几个小洞。 来自《简明英汉词典》
• The moths tapped and blurred at the window screen. 飞蛾在窗帘上跳来跳去，弄上了许多污点。 来自《现代英汉综合大词典》

7 wasp   

n.黄蜂，蚂蜂

参考例句：

• A wasp stung me on the arm.黄蜂蜇了我的手臂。
• Through the glass we can see the wasp.透过玻璃我们可以看到黄蜂。