Vicki
Generally by making sure that the trap seal is always filled with water you will eliminate most odors. When it is warm the evaporation goes even quicker. The best way to keep that trap filled with water is to either fill with water every other day or so (a real pain in the neck) or to install a trap primer. A trap primer installed at a toiletor other fixture that is used everyday somewhere in your house can put a small amount of water into that floor drain trap. Could be very difficult to install now though. Also, adding a small amount oil (cooking is non toxic) into the drain can slow the process of evaporation as it will float on top of the water of the trap slowing down evaporation.
