Is There Benefit in Removing Drops to 

 Prevent Within-orchard Buildup of 

 Apple Maggot Flies? 



Ronald Prokopy, Xingping Hu, Jian Duan, and Starker Wright 

 Department of Entomology^ University of Massachusetts 



The apple maggot fly is a key summer pest of 

 apples in eastern and midwestern regions of North 

 America. Ever since the advent of synthetic organic 

 insecticides, most orchardists have been able to 

 achieve effective control of apple maggot by apply- 

 ing two to four insecticide sprays during July and 

 August. Recently, we have developed a behavioral 

 approach to apple maggot control for use in large 

 commercial orchards. It involves surrounding an 

 orchard block with odor-baited red spheres placed 

 about five yards apart on perimeter apple trees. The 

 intent is to intercept flies immigrating from nearby 

 unmanaged host trees and thereby prevent them 

 from penetrating into the orchard interior. Flies 

 alighting on the spheres are killed either through 

 entanglement in a coating of sticky material on the 

 sphere surface or, using a new approach we have 

 been developing, through ingestion of a feeding 

 stimulant and insecticide on the sphere surface. 



In a recent survey in Massachusetts [Fruit Notes 

 60(4): 1-2], apple growers perceived several poten- 

 tial benefits arising ft-om use of this behavioral ap- 

 proach to apple maggot management as a substi- 

 tute for application of insecticide sprays. A poten- 

 tial shortcoming, however, is the danger that some 

 flies will not be intercepted by the perimeter traps 

 and will go on to oviposit within the orchard. Lar- 

 vae developing within the flesh of infested apples 

 could (following apple drop, larval exit, and puparial 

 formation in the soil) give rise to adults emerging 

 the next year within the confines of the orchard, 

 thereby compromising the value of perimeter inter- 

 ception traps. 



One way to counter the potential deleterious 

 effect of within-orchard fly emergence would be to 

 pick up dropped apples before larval exit (very rarely 

 do larvae exit from fruit hanging on the trees). In- 

 deed, picking up drops was considered to be the most 

 effective way of controlling apple maggot before the 

 advent of inorganic insecticides last century. To- 



ward this end, several researchers earlier this cen- 

 tury studied patterns of larval exit ft-om drops of 

 early, middle, and late-ripening apple cultivars wath 

 the aim of pinpointing frequency of need for drop 

 pick-up to prevent larval exit. None of these early 

 investigators, however, studied patterns of larval 

 exit from drops of important modern-day apple cul- 

 tivars. 



Here, we report combined results of studies car- 

 ried out in 1993 and 1994 of patterns of larval exit 

 from drops of four prominent cultivars represent- 

 ing a range from early ripening (Jersey Mac) to 

 middle (Mcintosh and Cortland) and late ripening 

 (Golden Delicious). Our primary intent was to de- 

 termine whether, for each cultivar, there was a 

 single point during the time period spanned by our 

 study that a grower could pick up drops and thereby 

 ensure that a great majority of larvae infesting to- 

 tal drops for the year would be removed before exit- 

 ing the fruit. 



Materials & Methods 



Our study was conducted in a commercial or- 

 chard slightly infested by apple maggot flies. In- 

 festation occurred as a consequence of suboptimal 

 deployment of odor-baited red sphere traps, which 

 permitted some proportion of flies to escape cap- 

 ture. Each year, ten trees of each cultivar were 

 designated randomly for removal of drops. Ten 

 drops per tree were removed on each sampling date 

 and pooled to comprise a total sample of 100 drops 

 for that cultivar on that date. To ensure that all 

 drops removed on a given date had fallen only since 

 the previous sampling date, we marked off a por- 

 tion of the area beneath each of the ten sampled 

 trees, and on each sampling date removed all drops 

 that had fallen into that area. Sampling dates were 

 about four weeks and two weeks before harvest, 

 harvest, and two weeks after harvest. In every case. 



Fruit Notes, Spring, 1996 



