Eyes On Plum Curculios: 

 Watching Them Behave 



Ronald Prokopy and Catherine Wirth 



Department of Entomology^ University of Massachusetts 



Shortcomings of black pyramid traps for 

 monitoring plum curculios described in the pre- 

 ceding article have stimulated us to take a closer 

 look at the behavior of individual curculios in 

 hopes of discovering why black pjrramid traps 

 perform less and less satisfactorily as the 

 curculio season progresses. In the 1997 Winter 

 issue of Fruit Notes, we described some pre- 

 liminary studies that led us to postulate that 

 perhaps curculios bypass pjramid traps under 

 moderate and high temperature conditions, fly- 

 ing directly into tree canopies rather than crawl- 

 ing or flying onto tree trunks or trunk-mimick- 

 ing pyramid traps. Here, we describe two stud- 

 ies conducted in 1997 in which we made exten- 

 sive direct observation of movements of plum 

 curculios toward host trees and p5rramid traps 

 under conditions as natural as possible for typi- 

 cal curculio behavior, while still permitting ef- 

 fective observation. 



Materials and Methods 



Curculios to be observed were tapped from 

 branches of unmanaged apple trees onto a 

 40x40-inch white bedsheet (first study) or a 

 16xl6-inch white bedsheet (second study) held 

 taut by staples driven into a wooden frame be- 

 neath. Apple foliage was scattered across about 

 15% of the surface area of each framed cloth to 

 provide hiding places for fallen curculios. Plum 

 curculios fall frequently from limbs of host trees 

 (sometimes more than once per day) onto the 

 ground beneath in response to perceived dan- 

 ger or adverse weather. We reasoned that tap- 

 ping curculios from branches and allowing them 

 to fall on cloth provided with shelter effectively 

 mimicked natural behavior and conditions. 



As soon as four or five curculios (first study) 



or eight curculios (second study) accumulated 

 on the cloth, we quickly but gently carried the 

 frame and cloth to a position half-way between 

 the trunk and canopy edge of a nearby semi- 

 dwarf unmanaged apple tree (first study) or 

 plum tree (second study). There were no 

 curculio traps of any sort in the vicinity of the 

 apple tree. One unbaited black p3rramid trap 

 was placed next to the trunk and another at 

 the edge of the canopy of the plum tree, with 

 the framed cloth centered between and equi- 

 distant (4 feet away) from either trap. Dressed 

 in white cap, shirt, and shorts that hopefully 

 were invisible to curculios, one of us knelt down 

 nearby the cloth and quietly observed the pro- 

 portion of curculios that departed the cloth by 

 flight or by crawling and the proportion that 

 moved to hide beneath foliage or rested on the 

 cloth. Observation periods lasted 1 hour. They 

 were evenly spaced among 1-hour intervals be- 

 ginning at 8 AM and ending at 8 PM in the first 

 study, or among 1-hour intervals beginning at 

 2 PM and ending at 6 PM in the second study. 

 In both studies, observations commenced a day 

 or two after petal fall and extended over a 3- 

 week period thereafter. We recorded the direc- 

 tion taken by each adult upon departure from 

 the cloth and continued to track adult destina- 

 tion until it was lost fi"om sight. 



Results 



Of the 166 plum curculios observed beneath 

 the apple tree, 52 (31%) left the framed cloth by 

 flight and 27 (16%) by crawling. The remain- 

 der moved to hide beneath foliage on the cloth 

 (18%) or rested in place (35%). Among curculios 

 that flew, significantly more (54%) flew toward 

 the tree canopy above than flew toward inter- 



Fruit Notes, Volume 63 (Number 1), Winter, 1998 



11 



