逻辑关系理不顺

Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways, so that it can feed on or otherwise harm new hosts.

这句话怎么也不理解，这里new hosts到底指谁？ biocontrol agent被引入怎么会破坏new hosts ?

----

上篇文章的开头有说到： More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests.

说明，所谓的 biocontrol agent就是insects, fungi, and viruses这一类东西，都是寄生在宿主身上的东西。所以,new hosts是针对nonnative biocontrol agent来说的，也就是新的宿主。