Elevation of pheromone response threshold in almond moth males pre-exposed to pheromone spray

High percentages of naive Cadra cautella (Walker) (Lepidoptera: Pyralidae) males not pre-exposed to pheromone flew upwind to sources containing 50 ng (83%) and 500 ng (97%) of pheromone, but not to sources containing 5 mu g (23%) and 50 mu g (4%). Of the naive males that flew upwind in response to 50 ng sources, 67% located and landed on the source, whereas fewer than 19% of the naive males that flew upwind in response to higher doses located and landed on the sources. A 2-minute pre-exposure of C.cautella males to a spray cloud containing 50 ng, 500 ng, 5 mu g or 50 mu g of pheromone, induced shifts in response levels such that in wind-tunnel bioassays performed 1 h later, there was an increase in the doses that optimally elicited upwind flight and landing on the source that was proportional to the pre-exposure dose. Few of the pre-exposed males flew upwind to (10-43%) and landed on (0-33%) 50 ng sources, whereas they now perferentially flew upwind to (58-81% and 52-73%) and landed on (33-68% and 55-60%) pheromone sources of doses of 500 ng and 5 mu g, respectively. Therefore preexposure to pheromone promoted a shift of threshold for response, and not an overall reduction in responsiveness to pheromone.