Red and black ants have infested my pooja room and consume the offerings meant for the Lord as well as the ‘kolam’. Is it okay to use insecticides to keep their numbers from swelling?

It is certainly a sin to kill ants in the pooja room. Scriptures say that if one kills small helpless creatures, one is bound to get skin diseases in the next birth.
The very act of drawing ‘kolams’ is so that ants and cows can feed on it. So it is not advisable to use insecticides in your pooja room.