Nearly all flies were caught on the ammonia source 

 that was upwind from the patch of hawthorn trees at 

 the time of testing. 



Testing of Commercial Bait 



In the second and third tests, our goal was to 

 determine the effectiveness of a commercial protein 

 commonly used in bait sprays, and to test the possibil- 

 ity of enhancing the attractiveness of such a commer- 

 cial product through increased release of ammonia. 

 This enhancement can be achieved either by raising 

 the pH, or through the addition of an ammonium com- 

 pound. 



Both of these tests were carried out in large field 

 cages, in the center of which we placed a hawthorn tree 

 about 1.5 meters tall. At a distance of 1 meter from the 

 center of the hawthorn tree, we placed in each of the 

 cardinal directions an apple twig with 10 leaves, fas- 

 tened to a pole. The outer foliage of the hawthorn tree 

 and the apple twig were about 20 cm apart. A cotton 

 wick, dipped 2 to 6 hours earlier into one of the treat- 

 ment solutions, was attached with a wire to the stem of 

 the apple twig. Ten mature females, protein deprived 

 for 6 to 8 days, were released in each replicate. They 

 were observed over a period of 80 minutes (rotation of 

 wick positions every 20 minutes) to quantify the num- 



ber of visits to the different wicks. 



In the second test we compared wa- 

 ter, a 0.1 molar solution of ammonium bi- 

 carbonate, the commercial fruit fly food 

 attractant Nulure™ (PIB-7) at the recom- 

 mended rate for ground bait sprays (a 1% 

 solution), and a solution (at the above 

 rates) of the two latter treatments com- 

 bined. Results of this test (Table 2) con- 

 firmed the attractiveness of ammonia and 

 the fact that flies move mainly upwind to 

 the source of the attractant. Surprisingly, 

 results also indicated a relatively poor at- 

 traction to the commercial food bait. 



In the third test we compared the 

 same treatments as in the second test, 

 except that for the ammonium bicarbon- 

 ate solution we substituted a 1% Nulure 

 solution in which we adjusted the pH 

 from 6.5 (that of the commercial product) 

 to 8.5. Results of this test (Table 2) again 

 showed that the addition of ammonium 

 bicarbonate increased substantially the 

 attractiveness of the commercial food bait 

 Nulure. However, the adjustment from a 

 slightly acidic pH to an alkaline pH of 8.5 

 did not increase, as expected, the attrac- 

 tiveness of Nulure. 



Conclusions 



The capture over 2 hours, at a distance of 4 meters, 

 of up to 60% of apple maggot fly females released in a 

 patch of hawthorn trees in the first experiment indi- 

 cates the strength of ammonia as a food-type attrac- 

 tant. The response to ammonia was largely influenced 

 by fly feeding status. Although flies do not feed on 

 ammonium compounds, ammonia produced by bacte- 

 rial breakdown of amino acids apparently serves as an 

 indicator to protein-starved flies that proteinaceous 

 food is present in the immediate surroundings. Since 

 these foods can be found in insect honeydew, flies 

 probably can detect these substrates in part through 

 the odor of ammonia released by them. 



In a food-rich natural environment, food-baited 

 traps for apple maggot flies must compete with natural 

 substrates. On the other hand, in orchards maintained 

 in a way that natural fly food is scarce (see the first 

 article in this series), the addition of a synthetic food 

 odor such as ammonium bicarbonate might increase 

 the attractiveness of certain fly traps, including pe- 

 rimeter interception traps. In such food-scarce or- 

 chards, it is possible that not only would mature fe- 

 males be retained by interception traps in perimeter 

 trees, but also that during their daily foraging for pro- 



Fruit Notes, Summer, 1990 



