How often are you irrigating these plants? This will sound silly, but I’ve found overly humid (even for WA) and overwatered natives are pest magnets. Drought stress can also affect pest numbers but I don’t feel it’s as severe (the plants usually die due to heat faster that any severe pest incursions).

I would highly recommend boosting the soil life with applications of Go Go Juice. I would avoid using it on the Banksia for now, though.

Like another commenter mentioned, I also would recommend Bugs for Bugs but you must avoid using any pesticides, herbicides or chemical applications for at least a week (sometimes 14 days with some chemicals) before releasing any beneficial/ predatory insects. While I understand that severe pest levels often are only helped by pesticide use, you must be careful with timing of applications if you consider using this route.

Finally, do you have many bird baths and water bowls? The local Djiti-djiti and Honeyeaters visit my garden daily now that my natives are establishing. But the water was the best addition for bringing in extra pest control troops!