Tesla Towers and Orbital Gas Strikes have been my go-to for clearing out the chaff from a bug breech. Chargers and titans will wreck the tower and walk straight through the gas, but everything else will get obliterated. Maybe I had some good luck with the gas strikes on my runs because the smaller bugs can't make it out of the gas before they drop dead, but then again, I usually use those as deterrents to keep them busy while I go somewhere else. Tesla is also great on the new defense missions if you can keep the bigger bugs away from them. My buddy and I held off all the bugs at the first two gates by ourselves with just Tesla Towers, EATs (for the bigger bugs), and autocannons. The vast majority of the time, we were calling down additional towers before the first ones even ran out.