This question was asked a few moments ago, and I am really tempted to click close as off topic, but since we are new here I wanted to check in with Meta.
I see no reason why pest control questions (whether varmints or insects) shouldn't be on-topic in the context of a gardening or landscaping question. In this case, he's asking about keeping them off his irrigation system, which sounds pretty on-topic to me.
Obviously, something like "How can I kill the mice in my walls?" or "How can I get rid of the bedbugs in my bed?" would be off-topic. Similarly, "How can I keep moths from nesting in my plenum-space fire sprinklers?" would be out of bounds.
I think it's on topic. Full disclosure though, it's my question. :)
The question pertains to maintaining my garden. I would also argue that installation and maintenance of sprinkler systems is an important part of landscaping. That's my $.02.