I'm getting mauled on mission 2 no matter what weapons I use - any suggestions. :)
This is the best strategy to kill those fucking grubs. For your loadout use the thermal projector, incendiary grenades, and any missile. Now for the strategy, gather them up in one place by kiting them. Kill those that are dangerously close to you. After you have gathered them launch your grenades towards them and use your thermal projector. Easy as that.
Akiyama Mizuki's advice is pretty good. Personally I find the scattergun is underrated for this mission. See if you can avoid them and have a lot bunch up together before firing, you want to take out as many as possible when they're in groups. Also try out the smoke grenades, they should stop when in the clouds allowing you to hit them easier.