Table 1. Fly survival and numbers of eggs laid 

 into hawthorn fruit or artificial fruit (i.e., wax 

 domes) by apple maggot flies confined to labora- 

 tory cages. 



Survival at Eggs produced/ 

 Treatment* 20 days (%) female/day 



Yeast & sucrose 



+ hawthorn fruit 86 

 Sucrose only 



+ hawthorn fruit 80 

 Sucrose only 



+ artificial fruit 80 

 No sucrose 



+ hawthorn fruit 



6.49 

 0.33 

 0.02 



'For each treatment, 6 immature females and 3 



immature males were released initially into each 



of 6 laboratory cages (replicates). All treatments 



had water. 



"The last flies died after 5 days in the laboratory 



cages. 



tions that included bird droppings and sucrose, or 

 insect honeydew, yielded any appreciable egglaying. 

 This result occurred also when flies fed solely on apple 

 leaf surfaces. As the latter was one of the feeding sites 

 of flies in our field observations, we hypothesized that 

 high mortality and no egglaying was probably due to in- 

 sufficient quantity of foliage placed inside the small lab 

 cages, rather than to the quality of whatever food was 

 present on leaf surfaces. 



Tests In Large Field Cages 



We decided to extend the previous laboratory as- 

 sessment to large field cages (3 meters high x 3 meters 

 diameter). Each field cage was covered by a tarpaulin to 

 prevent rain washing away food resources (although at 

 the start of each test, trees were hosed down with 

 water). In each cage, we placed a potted apple tree and 

 a potted hawthorn tree. They were of similar size 

 (approximately 1 .5 to 2.0 meters tall). The foliage areas 

 available to the flies were estimated by counting leaves. 

 Three field tests were run, each with a different set of 

 apple and hawthorn trees. 



For Field Test I, we used 4 field cages. In the first 

 cage we supplemented the flies' diet with sucrose and 

 yeast, in the second with sucrose and bird droppings, in 

 the third with sucrose only, and in the fourth with no 

 food. Flies were provided with hawthorn fruit as 

 egglaying sites. The results of this test (Table 2) con- 



Table 2. Fly survival and numbers of eggs laid 

 into hawthorn fruit by apple maggot flies con- 

 fined to field-caged apple and hawthorn trees in 

 Field Test I. 



Survival at Eggs produced/ 

 Treatment* 20 days (%) female/ day 



Yeast & sucrose 50 

 Bird droppings 



& sucrose 70 



Sucrose only 45 

 No sucrose 



no change of trees 



1.56 



0.43 

 0.15 



0.17 



"For each treatment, 20 immature females and 5 

 immature males were released initially. All 

 treatments were provided with water. 

 "The last flies died after 15 days in the field cage. 



firm the main findings of the lab tests. Again, bird drop- 

 pings in combination with sucrose yielded the greatest 

 amount of egglaying after the standard laboratory food 

 of yeast and sucrose. Interestingly, flies in the no- 

 sucrose treatment lived much longer than sucrose- 

 deprived flies in the laboratory tests. This result sug- 

 gests that flies find at least some carbohydrates on leaf 

 surfaces, although flies apparently used them up after 

 10 to 15 days of feeding. In both of these field cage 

 treatments, flies apparently obtained the proteins re- 

 quired to sustain a low level of egglaying from the 

 hawthorn fruit provided as egglaying sites. 



For Field Tests II and III, 7 field cages were used. 

 The following three treatments were added to those of 

 Test I: aphid honeydew (excrement) and sucrose; a 

 preparation of some apple leaf bacteria and sucrose; 

 and a no-sucrose treatment wherein trees in the cage 

 were replaced renewed every 4 days. With the excep- 

 tion of honeydew and bird droppings, all food (includ- 

 ing sucrose), was presented in a diluted form. Daily, 

 cages were searched thoroughly for predators and dead 

 flies. Every second day, all flies were recaptured, 

 counted, and released again, and all food was renewed. 



Results of Field Tests II and III (Table 3) were in 

 general very similar to those of Field Test I. Again, we 

 found no difference in survival between the sucrose- 

 only and no-sucrose treatments. Flies survived in these 

 treatments even longer than in field test I. These 

 results confirm once more that flies confined on caged 

 apple and hawthorn trees can apparently obtain suffi- 

 cient carbohydrates from leaf surfaces to satisfy some 

 basic energy requirements. This result may also ex- 



10 



Fruit Notes, Summer, 1990 



