Experimental evidence was obtained that T. tabaci is a major vector operating in the field occurrence of a destructive disease of pineapple plants in Hawaii and that this insect carries the virus to pineapple from certain weeds, of which Emilia flammea now appears most important. Preliminary evidence indicates that certain plants other than Emilia may be sources of the yellow-epot virus. The feeding of this insect upon pineapple plants appears to be incidental, and it is probable that any natural transfer of the virus from pineapple to pineapple is uncommon.