landlord is bringing chemicals for us to spray but i work 60 hours and don't have time to do it.
I agree. Proving you are not responsible is tough. You can always ask, but don't expect him to pay $$ if you won't try to help by spraying.
Personally, I'd be concerned about leaving it in my landlord's hands. Is he trained in pest control? What chemical would he plan to use? Would he handle the chemical properly and treat the area appropriately?
You say "us". Is that tenants in other apartments or your room mate? Is this a building-wide problem or just your apartment? You could spray (read the labels!) before you leave for work or your room mate could do it.
Regardless of the why's and wherefore's, I'd want those blood-sucking parasites out of my place as fast as possible and would do whatever it takes to make them disappear.
http://www.extension.umn.edu/distribution/housingandclothing/DK1022.html
http://cahe.nmsu.edu/pubs/_g/g-318.html