Table 3. Average fly survival and average num- 

 bers of eggs laid into hawthorn fruit by apple 

 maggot flies confined to field-caged apple and 

 hawthorn trees in Field Tests II and HI. 



Survival at Eggs produced/ 

 Treatment' 20 days (%) female/day 



Yeast & sucrose 

 Honeydew 



& sucrose 

 Bird droppings 



& sucrose 

 Leaf-bacteria" 



& sucrose 

 Sucrose only 

 No sucrose & 



no change of trees 

 No sucrose & 



change of trees 



every 4 days 



88 



63 



65 



73 

 68 



53 



63 



1.79 



1.14 



0.81 



0.43 

 0.42 



0.44 

 0.28 



'For each treatment, 20 immature females and 5 

 immature males were released initially. All 

 treatments were provided with water. 

 "Bacteria of the genera Bacillus, Enterobacter, 

 and Micrococcus. 



plain why in nature males have to leave the fruiting 

 host trees considerably less often than females to for- 

 age elsewhere for food. It is known that males need 

 little protein in their diet. Additionally, males are less 

 mobile and of smaller size than females. Their energy 

 requirements are consequently smaller. Therefore, 

 males need to consume less carbohydrates, which they 

 seem to be able to obtain mostly from host tree foliage. 



What is the origin of the carbohydrates that apple 

 maggot flies consume while feeding on leaf surfaces? 

 These may be minute residues of insect honeydews, or 

 plant fluids that regularly exude from leaf surfaces and 

 may contain carbohydrates. 



Both honeydew and bird droppings yielded levels 

 of egglaying considerably greater than those of other 

 treatments, although still below the optimal laboratory 

 diet of yeast plus sucrose. In all other field cage treat- 

 ments, flies apparently obtained the proteins required 

 to sustain a low level of egglaying from the hawthorn 

 fruit provided as egglaying sites. Once more, there was 

 no difference in female egglaying between the no- 

 sucrose treatments and the sucrose-only treatment. 

 Also the supplement of apple leaf surface bacteria and 



sucrose that we offered as a food source for flies did not 

 increase fly fecundity to any degree. This result is sup- 

 ported by a subsequent laboratory test with artificial 

 fruit, in which bacteria and sucrose yielded no eggs 

 whatsoever, similar to the result of the sucrose-only 

 laboratory treatment. 



After the results of Field Test I, we predicted that 

 by regularly replacing the tree foliage in cages not sup- 

 plemented with sucrose or other food, flies would not so 

 rapidly run out of whatever food might be present on 

 the leaf surfaces. This was not the case. Although the 

 difference was slight, the no-sucrose treatment with 

 replacement of the foliage showed the lowest female 

 fecundity in both Field Tests II and III. 



Another possible food source that we will consider 

 in future tests is bacteria of fly origin. Richard Drew in 

 Australia found that in a species of tropical fruit fly, 

 adults regurgitate fly-specific bacteria on fruit and 

 foliage. These bacteria then form colonies that spread 

 on plant surface nutrients, furnishing flies with pro- 

 tein of bacterial origin. 



Conclusions 



From these results, we can conclude that apple 

 maggot flies are able to gain at least some carbohy- 

 drates while "grazing" on leaf surfaces. As determined 

 from our field observations presented in the first article 

 in this series, flies actually do "graze" frequently on 

 leaf surfaces, though this feeding strategy appears to be 

 rather inefficient. Possibly, flies engage in this behav- 

 ior only in the absence of more readily available food 

 sources. Finding more concentrated sources of food, 

 such as insect honeydew and bird droppings, would 

 seem to be a much more efficient strategy. It would save 

 much time and energy, and gain appreciable time for 

 females to forage for fruit and to lay eggs. The fact that 

 we found females feeding at a distance from fruiting 

 host trees and a strong response of females to ammonia 

 odor (second article in this series) supports this inter- 

 pretation. 



Acknowledgements 



We thank Gabriela Gonzalez, Maryam 

 Mashayekhi, Patti Powers, Joshua Prokopy, Shifu Qu, 

 Barbara Richardson, and Jung Tang Wang for their 

 help during various aspects of these studies. Also we 

 wish to thank Richard Drew for encouraging this col- 

 laborative work, which was supported by the Science 

 and Education Administration of the USDA under 

 grant 8700564 from the Competitive Grants Office, and 

 by the Massachusetts Agricultural Experiment Station 

 Project 604. 



Fruit Notes, Summer, 1990 



11 



