If you can't achieve a 100% kill rate over some area, and progressively expand that area, what's the goal of working against it at all? A pest invasion isn't going to get dispirited and retreat when it takes 30% losses, like a foreign military might, it's going to heal its population losses and go right back to being limited by other factors in a matter of weeks or months.
I spent a term paper five years back pondering our response to bark beetles before concluding that the entire campaign to 'control' the infestation was basically a means of permitting the logging industry to log areas that we would not otherwise want logged, financed with political capital from the environmentalist movement. I see that other people are catching on to this narrative as well:
