Easily done solo at level 20.
Extreme Difficulty, Bug Mission, Thin the Swarm (Kill X Bugs).
I went with Railgun, Shield Pack, Orbital Railgun, and Orbital Laser. Breaker Shotgun, SMG, and High Explosive Grenades.
Pick the Trailblazer Scout Armor/Helmet for Speed/Stam Regen.
Run circles around all the bugs/starting area, mowing down the small/medium bugs. If a Charger spawns, Railcannon. Drop a laser on the opposite side of the arena. Armor spawns just give it a quick railgun snipe if you have to. I didn't even have to use a single stim with this method, and had 60% time left.