We have been brought up to fear insects.这句话里面的to fear insects说是做we的补足句,to 是什么用法为什么用to

We have been brought up to fear insects.这句话里面的to fear insects说是做we的补足句,to 是什么用法
为什么用to

to 是bring up 转换为被动语句后,在与后面动词连接中加的介词