Plum Curculio (Coleoptera: Curculionidae) Responses to Unbaited Pyramid and Cone Traps

Abstract

We evaluated responses or adult plum curculios, Conotrachelus nenuphar (Herbst), to black unbaited pyramids (111 cm tall) capped by conical boll weevil trap tops and placed at various locations on the ground in a small commercial apple orchard or in patches of unsprayed apple trees in Massachusetts. Pyramid traps adjacent to apple tree trunks captured significantly more adults than those between apple trees, those between apple trees and an adjacent woods, and those between apple trees and an adjacent open field. Also, they captured significantly more adults than unbaited conical boll weevil trap tops placed on cut ends of vertical twigs or in other positions in apple tree canopies. Further tests revealed that the nature of the ground cover (bare soil or short grass) beneath or between tree canopies had no detectable effect on captures by pyramid traps, whereas captures decreased significantly as traps were placed further from the tree trunk. Indirect evidence from additional tests with pyramids and direct evidence from observations of released adults permitted classification of responses to pyramids according to curculio arrival by flight or by crawling and according to arrival during light or darkness. Together, these provided a possible explanation for lack of effect of ground cover but significant effect of trap location on captures. Even at the most favored location (next to tree trunks), daily captures on pyramid traps failed to correlate positively with daily incidence of injury to fruit caused by plum curculio feeding or egglaying, suggesting that further research is necessary before unbaited pyramid traps can be recommended for use in monitoring plum curculio populations in commercial apple orchards in Massachusetts.