The importance of ammonia in proteinaceous attractants for fruit flies (Family: Tephritidae)

The responses of the Queensland fruit fly to food-based lures were studied, with particular emphasis on the importance of ammonia as an attractant or repellent. Certain solutions of ammonium bicarbonate were found to be highly effective attractants for the Queensland fruit fly, provided they were tested in traps in which the retention of the flies did not depend on their contacting the bait solution. The attractancies of such solutions were found to be strongly dependent on concentration and pH, and mean attractancies more than five times that of the commercial protein hydrolysate used as a standard were obtained. Highest attractancies were associated with ammonia evolution rates in the region 5-25 �l ammonia (s.t.p.) h-1 100 ml-1 of solution; rates above 400 �1 ammonia (s.t.p.) h-1 100 ml-1 appeared to be repellent. The addition of a mixture of amino acids to the ammonium bicarbonate solutions under these trap conditions had no significant effect on their attractancy; but the addition of the standard protein hydrolysate to a 0.001 M solution of ammonium bicarbonate, with pH adjusted to 8.5, produced an outstandingly effective lure, with a mean attractancy almost nine times as great as the standard hydrolysate alone at its normal pH of 4.8. Subsequent experiments showed that simply raising the pH of the standard protein hydrolysate to 8.5 caused a similar high attractancy, which could be due in part to the marked rise in ammonia production from endogenous sources. Protein hydrolysate solutions showed pronounced increases in both ammonia production and fruit fly attractancy when microorganisms were allowed to flourish. No such increases occurred when the microorganisms were inhibited with a preservative. Evidence is also presented which indicates that carbon dioxide is mildly repellent to the Queensland fruit fly.