Does it actually work properly? In my 1st game I've got everyone in federation except thoraxians, who are real bad-asses WRT ground combat. Orbital bombardment doesn't seem to do anything at all, though. There's 17k power fleet on their orbit which kills all of 500 ants per day..
Does the "25x => 2.5x" change actually work on existing saves?
[Assumes generic anti-bug voice from <your choice of franchise here>]
To destroy bugs you have three choices!
You make the other race who has a chance to ground pound against them their enemy, in other words allow the burlusts to invade!
OR, you bombard them eventually with the birds, so you get the peltians space superiority.
Or, you get the someone to lob superweapons against them (was the actuians? i think so. Or maybe the other isolationists, one of them)
In general, diplomatic isolation is your best best. Or, just smash their fleets, eventually your allies will come up with a plan.