Fruit Odors Are More Attractive tlian 

 Conspecific Odors to Adult 

 Plum Curculios 



Tracy Leskey, Monica Elmore, Anthony Minalga, Beata Rzasa, E. Fidelma Boyd, 



and Ronald Prokopy 



Department of Entomology, University of Massachusetts 



Many species of weevils are attracted to host plant 

 odors and to weevil-produced aggregation and/or sex 

 pheromones. In many cases, when host plant odors 

 and pheromones are deployed in combination, weevil 

 attraction is greater than to either odor type alone. Plum 

 curculios (PCs) have been shown to be attracted to host 

 fruit odors and to a male-produced aggregation phero- 

 mone, grandisoic acid, identified in PCs by Eller and 

 Bartelt of Illinois, but little is known about the level of 

 PC attraction to a combination of host fruit and phero- 

 monal odors. 



Successful monitoring systems deploying both host 

 plant and pheromonal odors have been created for sev- 

 eral species of weevils. Although a reliable monitor- 

 ing system for detecting adult PC entry into orchards 

 from overwintering sites does not exist, the deploy- 

 ment of attractive odors such as those from host fruit 

 and/or pheromone in conjunction with a trap that is 

 also visually attractive to adult PCs could prove to be 

 successful. 



In the 1998 Winter issue of Fruit Notes, we pre- 

 sented preliminary results from bioassays conducted 

 in large Plexiglas arenas designed to assess PC attrac- 

 tion not only to fruit odors but also to odors emitted by 

 other PCs. Here we provide more detailed results of 

 PC attraction to fruit odors, odors emitted by other PCs, 

 synthetic grandisoic acid, and fruit odors combined 

 with odors emitted by other PCs or with synthetic 

 grandisoic acid. 



Materials & Methods 



Large clear Plexiglas arenas with dimensions of 

 24x24x12 inches and Plexiglas lids were used as still- 

 air arenas for the following experiments. Source ma- 

 terials to be tested as emitting potentially attractive 



odors were placed in small cotton bags hung in the 

 upper comers (one per comer) of each arena. 



Either ten male or ten female PCs starved for 24 

 hours and chilled 30 minutes prior to testing were re- 

 leased into the center of an arena at the beginning of 

 darkness. Numbers of PCs that crawled to within one- 

 half inch of an odor source held inside a cotton bag 

 were recorded every 1 minutes for 1 hour. Each trial 

 was repeated at least eight times, each time rotating 

 the position of cotton bags containing odor sources. 



Treatments tested as potentially emitting attractive 

 odors included five freshly picked wild plums, five 

 male or female PCs, synthetic grandisoic acid impreg- 

 nated into small mbber septa (at a low and a high dose 

 of 0.03 ug and 3.00 ug, respectively), or five wild plums 

 in combination with five male PCs, five female PCs, 

 grandisoic acid at a low or high dose, or a green fmit 

 worm (GFW) larva. A GFW was used to simulate 

 plums that had been fed upon by a non-PC insect be- 

 cause we wanted to leam if odor released from plums 

 that were being fed upon by PCs and/or odor from PCs 

 that were feeding on plums was attractive to other PCs. 



The total number of PC responders to a particular 

 odor treatment was tallied over the six 10-minute in- 

 tervals for each of the four treatments to provide a to- 

 tal response score for each treatment for every experi- 

 ment. Results presented here reflect the mean number 

 of PCs attracted to each treatment over all total response 

 scores. 



Results 



Male Responses to Females. In Arena One (Table 

 1 ), males did not respond to the odor of females alone 

 compared to controls, but in Arena Two, males re- 

 sponded to odor of females held with plums in signifi- 



Fruit Notes, Volume 64 (Number 3), Summer, 1999 



