Exterminator sprayed a month ago. Still roaches. Can I put down traps and boric acid?

So I'm subletting an apt in West Los Angeles (I see in many roach questions they ask location) and I'm on my last month. Since last month we've started seeing roaches. They don't seem to go for the food... I've seen them in my room, the kitchen floor, living room, but never on or near food,... show more So I'm subletting an apt in West Los Angeles (I see in many roach questions they ask location) and I'm on my last month. Since last month we've started seeing roaches. They don't seem to go for the food... I've seen them in my room, the kitchen floor, living room, but never on or near food, strange (All my food is in tupperware anyway, not taking chances)

So it wasn't a bad infestation, it could be anywhere from waking up in the morning to find 2 - 3 roaches scatter, or at night lifting a thing like my suitcase and one runs out from under it. And it could also be totally scarce for like a week. Each night I'd come home and go through the routine of checking places. What's also weird is they'd never be upstairs. Only the bottom floor.

It's a clean, big, mostly hardwood floor apt, and when I told the landlord about it he said they're waterbugs that come in from the rain. When they kept showing up though he got us an exterminator, who put down residual insecticide (I think) (It required us to put all of our stuff in a pile).

After that all I've been finding are dead roaches and roaches on their backs. I called the exterminator and he said this was normal because the spray numbs them or something so they can't walk right and they should be gone in a few days or weeks, and not to use additional measures.

Well it's been a month and though we had about 2 weeks of nothing, I'm starting to find 2 - 3 big ones dead or dying on their backs every day or two. They are about the size of my thumb, and...hmm I'll take a pic for you but I believe it's the American Roach. It's big, reddish and blackish

http://imgur.com/fAiVH.jpg

Also, I've sealed every crack in the wall / floorboard I could find with tape. If there's thousands in the walls I don't see how they could get out...
My roommates don't want to talk to the landlord again (and it's a joint effort or nothing) to get the exterminator back, so we're going to put down boric acid (also possibly salt, I've heard this works) and traps and hope they're gone.

Has it been enough time since the exterminator sprayed to do that without erasing what he did? Is that whole "erasing what they did" thing a ploy to get them to keep coming back in the first place?


Also how exactly can I kill these things? I know not to crush them because of the whole eggs spreading thing, and right now I'm pretty content on my method of putting them in a cup, filling the cup with water (but they dont drown. THEY NEVER DROWN), and adding dish soap, then they seem to die instantly, then flushing them.


Oh sorry one more thing. This is my 2nd apt out of many future ones in SoCal I've had roaches. The 1st one I believe was German or Oriental, small, black, fast.) And that was much much worse. We had em coming out of plugs and stuff, but that place was dirty, so it fit..... It's possible I might be carrying them (even though I've never seen a roach in my life until I lived here). How do I prevent taking these roaches to my next apt?

Thanks.

TLDR; American Roaches in apt. Sprayed about a month ago. Can't get exterminator. Can we treat it ourselves?
Update: I have sealed up all spaces under the bathroom sink that had holes with tape. We still have vents though, 3 in the living room, 1 in my room and the bathroom and the kitchen. I can't imagine how to seal those without it looking like a disaster zone, so I'm going to believe they're not coming from there.
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