题型：阅读理解 题类：常考题 难易度：普通
人教版（新课程标准）高中英语必修3 Unit 2 Healthy eating 同步练习2
There are lots of insects that farmers hate. But there also are some they like. They protect crops against damage from other insects. A good example is the lady beetle, which is also known as the ladybug(瓢虫)．
Lady beetles are a natural control for aphids(蚜虫). Lady beetles are red, orange or black. They often have black spots, though some have light colored spots. Different kinds of lady beetles have different numbers of spots. There are lady beetles with four, five, seven and fourteen spots.
Many of the well-known kinds of lady beetles come from Asia or Europe. They now are common throughout the United States.
American scientists imported one kind of lady beetle, the multicolored Asian lady beetle, as early as 1916. They released them as an attempt to control some kinds of insects. Over the years, the beetle has become established, possibly helped by some that arrived with imported plants on ships.
Experts say over 450 kinds of lady beetles are found in North America. Some are native to the area. Others have been brought from other places. Almost all are helpful to farmers.
The Asian lady beetles now in the United States probably came from Japan. The Asian lady beetle eats aphids that damage crops like soybeans, fruits and berries.
In the southern United States, Asian lady beetles have reduced the need for farmers to use reskilling poisons on pecan trees. This popular tree nut suffers from aphids and other pests that the lady beetles eat.
But some people say the Asian lady beetle has itself become a pest. They worry that the lady beetles may eat their late autumn fruit crops.
Experts say Asian lady beetles may appear in large numbers in some years. But they say the insects are too helpful to be considered as pests.
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