There's a lot of concern that once you start using artificial pesticides,

很多人担心一旦开始使用人工杀虫剂
that you have to use more artificial pesticides

就必须不断加量
because here's what happens.

事实正是如此
The pesticides get applied to crops and they work;

杀虫剂用于作物很有效
except they don't kill everything,

但它们并没杀死所有害虫
and insects evolve to resist a particular pesticide.

其中一些进化成具有特定的抗药性的害虫
These particular pests that are resistant to that pesticide

这些对某类特定杀虫剂具有抗药性的害虫
will prosper in very large numbers,

将会大量繁殖
especially in areas where monoculture is the reign of the day.

特别是在那些以单一栽培方式为主的地区
By monoculture we mean raising one crop in vast acreages,

单一栽培即在广阔的面积上栽种一种作物
so I'll talk about biodiversity in the next class

下节课我们会谈到生物的多样性
and we'll talk about the state of Iowa as an example

以爱荷华州为例