John, I think your buddies only gave you 1/3 of the solution. Roaches are generally "30-30-30" critters. That is, it takes them 30 days in the egg to hatch
, 30 to mature, 30 for the next generation to be born and repeat the cycle.
Once you have roaches, you don't know if they have already left you any eggs. So in order to make sure you've got them all--especially with pyrethrins which leave no residue and won't kill eggs--you need to "kill now, repeat in 30 days, repeat in 30 days" in order to make sure you've gotten the whole cycle of them. If one set of bombs kills them "forever" you've gotten lucky.
I learned this from the son of an entymologist, who was a telephone lineman. Familiar with finding critters in all the places phone
The bait traps are also good for control, since they'll keep killing any strays that come in, pretty quickly. They work physically (like boric acid) by cutting holes in the carapice so the bugs dehydrate and die. That prevents them from building up any resistance to chemicals, too.