Evidence of a Replete Caste in the Fire Ant Solenopsis invicta1,2

Abstract

About 3 years ago, we collected some workers and alates from a field colony of the fire ant Solenopsis invicta Buren that had been fed soybean oil containing blue dye one year earlier, and gave a portion of the collection to Virgil Owens, Animal and Plant Health Inspection Service, USDA, at Gulfport, Miss. Mr. Owens subsequently called to our attention that large amounts of a blue substance were visible in the crops of the largest major workers, in the crops and wing veins of alate females, and in the crops of a few minor workers. Indeed, the abdomens of these major workers were so distended that they could be easily picked out with the naked eye. Subsequent chemical tests showed that the substance was an oil-dye mixture, which was puzzling because the oil and dye would not have been present if normal food exchange, metabolism, and excretion had occurred after the initial feeding of the ants. The present paper reports the results of the studies we made of this phenomenon.