Sources of Apple Odor Attractive to Adult Plum Curculios

We evaluated olfactory attraction of overwintered plum curculio (PC) adults, Conotrachelus nenuphar, to volatiles from extracts of host and nonhost plant tissues in the laboratory using a still-air dual-choice bioassay system. In experiments evaluating four different solvents, hexane and water proved to be better than dichloromethane and methanol for extracting nonpolar and polar attractive compounds, respectively, from host McIntosh apple tissues. Significantly more PCs were attracted to volatiles from hexane extracts of host wild plum fruit at bloom, and host wild plum and McIntosh fruit at two weeks after bloom, than to volatiles from hexane extracts of nonhost honeysuckle fruit at either phenological stage. In every case, for hexane-extracted or water-extracted volatiles from McIntosh apple tissues (twigs, leaves, or fruit) at seven phenological stages of development (pink through five weeks after bloom), greatest numerical responses were recorded to volatiles from extracts made between bloom and two weeks after bloom. We conclude that source material used to identify volatile components of McIntosh apple odor attractive to PCs should be collected between bloom and two weeks after bloom.