Plum Curculio Responses to Host Fruit 

 and Conspecific Odors 



Tracy Leskey, Amy Wiebe, Susan Nixson, and Ronald Prokopy 

 Department of Entomology, University of Massachusetts 



Many species of weevils are attracted to host 

 plant odors and use them in host finding. Fur- 

 ther, many species of weevils produce aggrega- 

 tion and/or sex pheromones. Plum curculios 

 (PCs) have been shown to be attracted to host 

 fruit odors in the laboratory over short distances 

 and in the field at distances up to 3 yards. Fur- 

 ther, a male-produced aggregation pheromone, 

 grandisoic acid, was recently identified in PCs 

 by Eller and Bartelt of Illinois. 



At present, a reliable monitoring system for 

 detecting adult PC entry into orchards from 

 overwintering sites does not exist. However, if 

 attractive odors such as those from host fruit 

 and/or pheromones were employed in conjunc- 

 tion with a trap that was also visually attrac- 

 tive to adult PCs, then a reliable monitoring 

 device could be created as has been done for 

 other species of weevils. 



In the 1996 and 1997 Winter issues of Fruit 

 Notes, we reported on results of laboratory 

 Petri-dish bioassays that addressed responses 

 of adult PCs to odors emitted from Mcintosh 

 apple trees. Here, we present results from bio- 

 assays conducted in large Plexiglas arenas de- 

 signed to assess PC attraction not only to fruit 

 odors but also to odors emitted by other PCs. 



Materials and Methods 



Large clear Plexiglas arenas with dimen- 

 sions of 24x24x12 inches with Plexiglas lids 

 were used as still-air arenas for the following 

 experiments. Materials to be tested as emit- 

 ting potentially attractive odors were placed in 

 small cotton bags hung in the upper corners (one 

 per corner) of each box. Originally, we tried 

 testing PCs with cotton bags placed in lower 

 corners of arenas, but found that because of the 

 natural tendency of PCs to crawl upwards, 

 hanging the bags in upper corners was a more 

 effective means of testing PCs. 



Either ten male or ten female PCs starved 

 for 24 hours and chilled 30 minutes prior to test- 

 ing were released into the center of a box at the 

 beginning of darkness. Numbers of PCs that 

 crawled to within one-half inch of an odor source 

 held within a cotton bag were recorded after 1 

 hour. Each experiment was repeated three 

 more 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 wild plums plus five male or 

 female PCs, five male or female PCs alone, five 



Fruit Notes, Volume 6,3 (Number 1), Winter, 1998 



