THE WALNUT HUSK FLY: A "NEW" PEST OF PEACHES IN MASSACHUSETTS 



William M. Coll, Ronald J. Prokopy, and Kathleen Leahy 



Department of Entomology 



University of Massachusetts 



Peaches are grown by many commercial orchard! sts in Massachusetts, and 

 typically are marketed directly to consumers at on-farm stands. While the 

 total size of the state's peach crop is quite small, compared to states to 

 our south, the retail price of this fruit certainly justifies the effort of 

 growing it, especially because peaches are the first tree fruit crop to 

 ripen and find its way onto local shelves in any quantity. 



Under our conditions, winter and spring temperatures are the major fac- 

 tors limiting peach production inasmuch as most growers usually have little 

 difficulty controlling the major peach pests: brown rot, catfacing plant 

 bugs, plum curculio, green peach aphids, and borers. 



Consequently, we reacted with great interest when we received a call in 

 early September from a commercial grower in Granville, Massachsetts, who 

 reported observing an unknown fruit fly, active and causing substantial 

 injury to his peaches. In addition, another grower in the Wilbraham area 

 reported sighting similar flies active in his peach block during harvest, 

 although no fruit injury was observed. 



Adult specimens sent to us were identified as the walnut husk fly 

 (WHF), Rhagol et i s suavi s Loew, a Tephritid fly related to the apple maggot 

 (AMF), R^ pomonel la , and the blueberry maggot, R_^ mendax . WHF had been 

 reported to cause injury to peaches at two unrelated sites in New York State 

 in 1968 (2). 



The intent of this article is to provide information about the fly's 

 life history and general appearance, a description of injury to peach, and 

 available monitoring and control options. We conclude with a discussion of 

 the potential of this fly to become a serious pest of peaches. 



LIFE HISTORY AND. DESCRIPTION 



In New York (3), WHF is reported to emerge from pupae in the soil about 

 July 15, somewhat after first emergence of apple maggot adults. Adult 

 females (Fig. 1) are about 4 mm in length, and are slightly larger than 

 males. The adult fly is a tawny brown color with a yellow spot on the back. 

 The wings have three prominent dark bands, one of which extends around the 

 wing tip to form a "V" shape. Like AMF, there is only one generation per 

 year. Adult WHF emergence continues until about mid August. Unlike its 

 relatives, R_^ suavi s is reported to utilize as its normal hosts black, 

 Persian, and Japanese walnuts, and butternuts. Eggs are initially white, 

 somewhat curved, and measure about 0.9 nim x 0.3 mm. On wild hosts, 

 egglaying occurs during August, and the nearly transparent to cream-white 

 larvae feed within the husk (exocarp) of the nut and emerge from husks from 

 about September 1 to November 1. Pupae resemble grains of wheat. Pupation 

 occurs in soil at depths of from 1/2 to 1 1/2 inches, with emergence of most 



