Hi Cooran, if there's a Home Depot near your home, you could just stop by to ask the folks there and get lots of valuable free consultation about your problem. You still need to identify the exact kind of borers though (your pest control professional's gonna have to do this anyway in order to find the right chemicals to kill them). Can't hurt to try the electronic devices first, they're pretty cheap to get (~10 bucks in the States, don't know the price in Australia though), and if it works, the price tag will be just a fraction of the cost of professional chemicals. Also check out the natural pest repellents site here: http://www.ghorganics.com/page9.html
. In the worst case scenario, have the experts do their stuff, you wasted 10 bucks on the electronic device and maybe a few bucks on lemon/onion skins for natural repellents, but with the peace of mind that at least you've tried. Good luck..