BIOASSAY APPROACHES TO ASSESSING BEHAVIORAL-RESPONSES OF PLUM CURCULIO ADULTS (COLEOPTERA, CURCULIONIDAE) TO HOST FRUIT ODOR

We evaluated several approaches to developing a simple, sensitive, and reliable laboratory bioassay of responses of overwintered adult plum curculios (PCs), Conotrachelus nenuphar (Herbst), to host fruit odor o r its attractive components. A high proportion of assayed PCs responde d positively to odor of wild plums under no-choice, moving-air conditi ons in a wind tunnel and under dual-choice, still-air conditions in en closed Petri dishes. Positive response to controls lacking host odor, however, was much greater in the wind tunnel, arguing in favor of bioa ssays under dual-choice conditions in still air to provide greater PC discrimination. Response to host odor (from wild plums or hexane extra ct of wild plums or Liberty apples) in Petri dish bioassay chambers pr oved greatest: (1) during the scotophase of PCs under total dark or di m red light conditions, (2) when Petri dishes were completely enclosed , (3) when PCs were starved for 24 or 48 hr, and (4) when PCs were tes ted within seven weeks after apple tree petal fall. Neither the sex of a PC nor the direction in which a PC was obliged to move to find the source of host odor (upward through a port in the Petri dish lid or do wnward through a port in the base) had a substantial effect on level o f response to host odor or discrimination of host odor from a nonodoro us control. We conclude that an enclosed Petri dish bioassay chamber o f the type described here should be a valuable asset in the process of chemically identifying components of host fruit odor attractive to PC s.