OE


As its name should tell you, an invasive species is an organism that is not native to a particular place but has moved in and is disrupting the local ecosystem. It is a threat to local plants and animals, so the first blank probably means something like native. Inveterate means firmly established by long continuance, but it more commonly refers to feelings, practices, or even diseases than it does to plants or animals. Pugnacious means quarrelsome or combative; there is nothing in the passage to suggest that native species are unusually aggressive, so you should eliminate it. This leaves you with indigenous, which means originating in and characteristic of a particular region and is the best answer.
To fill in the second blank, you simply need a general sense of the passage's point - that invasive species are harmful. Covert means concealed or secret. It is clear from the passage, however, that at least some invasive species have a very obvious effect on the environment (see, for example, the description of the emerald ash borer), so you should be able to eliminate this choice. Perfidious, on the other hand, is too strong a word; it means treacherous or disloyal and implies a malicious intent that insects presumably do not have. Deleterious, or injurious, is the best choice.