Table 2. Apple maggot flies observed during 4 

 weeks feeding on fruiting apple trees and on non- 

 fruiting host trees and other vegetation in an 

 abandoned apple orchard. 



Percent of 

 individuals feeding on 



Fruiting Other 

 host trees vegetation 



Number observed 

 Week feeding 



1 



2 

 3 

 4 



120 



110 



103 



77 



29 

 45 

 34 



42 



71 

 55 

 66 

 58 



Formerly it was thought that aphid or leafhopper ex- 

 crement (honeydew) on foliage was the principal food 

 of apple maggot flies in nature; however, we never de- 

 tected any droplets of honeydew on the plants observed 

 in this study area. 



One of our most important findings was the obser- 

 vation of considerable fly feeding on bird droppings, a 

 probable source of nitrogenous compounds, which are 

 essential for egg development. Droppings were found 

 on a variety of fruiting plants, including apple trees. 

 Fruiting buckthorn (Rhamnus) was the main non-host 

 feeding site. Birds were attracted to buckthorn bushes 

 having ripe berries and favorable perching sites. Here, 

 it was common to see flies feeding on bird droppings, 

 dropped fruit pieces, and leaf surfaces. Competition 

 with other apple maggot flies and other types of flies for 

 these food sources on buckthorn was observed on sev- 



era! occasions. 



Later in 1987, additional observations were made 

 in a grove of wild hawthorn trees near Geneva, NY, and 

 on hawthorn trees on the campus of the University of 

 Massachusetts at Amherst. In the first case, the pat- 

 tern of findings was similar to the one described above 

 (i.e., the flies left fruiting host trees regularly in search 

 of food). In the second case, however, one of the fruiting 

 hawthorn trees had shiny leaves with plenty of aphid 

 honeydew. Here, flies were seen feeding on the honey- 

 dew, mating, and ovipositing. They appeared to con- 

 centrate more of their activites on this tree. 



In general, we observed apple maggot flies spend- 

 ing considerable time in apparent indiscriminate for- 

 aging for diffuse food sources on leaf surfaces of host 

 and non-host trees. This "grazing" type of feeding may 

 be typical of apple maggot flies under conditions of 

 scarcity of honeydew or other carbohydrate and pro- 

 tein resources. Such adjustment in food foraging activ- 

 ity in response to dynamic changes in the spatial, 

 temporal, and seasonal distribution of food resources 

 (for example after rains), probably also bears upon the 

 variable effectiveness of such management tools as 

 food-baited monitoring traps and insecticidal-bait 

 sprays. 



Our study has shown that in the absence of abun- 

 dant food resources on fruiting host trees, flies leave 

 hosts during the sexual maturation period. Even after 

 the onset of egglaying, females continue leaving food- 

 scarce hosts in the absence of nitrogenous food to 

 forage in the surroundings. Odor from highly concen- 

 trated food sources may direct this searching behavior 

 (the second article in this series gives further informa- 

 tion on this subject). 



Implications for Orchard 

 Management 



There are various ways that some of our 

 findings on apple maggot fly food foraging 

 may contribute to successful implementa- 

 tion of the second stage of the apple IPM 

 program. One is maintaining orchards pur- 

 posely scarce of natural food resources by 

 adjusting pruning practices to discourage 

 formation of fresh sprouts and attendant 

 buildup of aphids on the sprouts. Another is 

 discouraging flocks of birds from entering 

 orchards through use of Scare-Eye bal- 

 loons. Fewer birds would result in both 

 fewer wounded fruits and fewer bird drop- 

 pings as sources of food for adult flies. 



In food-scarce orchards, immigrating 



Fruit Notes, Summer, 1990 



