Remember that moth from earlier? Now you can drop it out of the sky. It's locked in a flight pattern over this steep cliff, swooping by every so often and knocking crap around. Scaling this cliff, swarming with hives and peppered with bits of broken concrete, isn't too hard, but if you're caught in the moth's path you stand a good chance of getting knocked all the way back down. But, the bottom is where we're gonna start anyway, so be sure to run all the way down first path (north like) to find the first token, the letter "R."
After a bit of climbing, you'll come to a small building that's got a hive plopped right in the middle, surrounded by barrels. Fry 'em and you'll see another "R" target mark floating inside. To finally be rid of the moth menace, continue to the very top (be sure to grab the laser rifle hiding in plain sight), look down for a rocket launcher on a narrow piece of concrete (you passed it earlier) and rappel down to it. Now, with rocket launcher, laser rifle and a mountaintop firing position, blow out the moth's back end and then its midsection. We finished it off with a laser rifle blast to the face and it went down, so perhaps you don't have to aim directly at its body. Much, much easier than the worm.
Before heading into the cave, collect the "A" target mark, located just outside the topmost room. If you stand where the laser rifle was, look up and northwest. The mark is up there, just out of site. Next, it's into a large cave filled with, you guessed it, more bugs.
There's a data post right away and then a VS off to the right. Get the post, but head into the pit below for more ammo, another VS and the "A" target (it's under the giant stone stairs). Take your VS up and out, blast down the new wasp enemies and after a bit of walking you'll see another data post in reach. But, check to the right - there's a cave filled with stalactites and, more importantly, a "U" token floating near the ceiling. If your VS is about to pop, consider switching it out for the fresher one found in this cave.
Keep on down the path with your VS. Eventually you'll enter a room with a massive blue icicle standing in the middle. Look in the northeast corner for "O," hit up the rooms on either side for ammo and move on to the boss battle.
This... would be the biggest thing in the game thus far. That doesn't make it any more difficult, though. Aim for either its large or small arms to tear them away - after sufficient damage, the bug'll drop down in pain, revealing a soft, vulnerable weak point on its head. Anything you blow off will grow back, so keep the ammo coming. Large stalactites just happen to be hanging directly over this bug, so shooting those down can do a little extra damage. Keep firing, watch out for the ice attack and you should bag this bug in no time.
Be sure to come back next week for the remaining levels - all the targets marks and boss battles shall be revealed in just a few short days.