Concentration of air-borne pheromone required for long-lasting peripheral adaptation in the obliquebanded leafroller, Choristoneura rosaceana

Electroantennogram (EAG) responses of male obliquebanded leafrollers, Choristoneura rosaceana (Harris), to the main component of its pheromone blend and traces of geometric isomer ((Z)11-14:Ac and (E)11-14:Ac, respectively) were recorded before and after 1 h of continuous exposure to pheromone in laboratory experiments, and 24h of exposure under field conditions. Concentrations of pheromone ranging from 56 to below 1ngmL 1 air in Teflon chambers with regulated air exchange reduced peripheral sensory responses by 40–60% as measured by amplitudes of the EAG. Adaptation did not increase in a dosage-dependent fashion over most of this range; an identical reduction of responsiveness was observed at each exposure to an effective concentration. Exposure of C. rosaceana at a loading dosage of 1 ng of pheromone in 100mL of mineral oil (air concentration below the GLC detection limit) did not induce measurable adaptation. Caging C. rosaceana in apple trees adjacent to one, two or four Isomate OBLR/PLR Plus polyethylene pheromone dispensers for 24h resulted in long-lasting adaptation similar to that seen in laboratory experiments. Adaptation was not observed forC. rosaceana caged at a distance of 2m from Isomate dispensers in 1-ha plots treated with 500 dispensers per ha. Whenever observed, this type of adaptation was expressed for more than 5min after exposure to pheromone ceased. Collectively, this adaptation phenomenon in C. rosaceana is consistent with the third of Zufall & Leinders-Zufall’s types of olfactory adaptation that is ‘long-lasting’. Although the dosage of pheromone required to induce long-lasting adaptation in this moth is judged high relative to that for normal sexual communication, we suggest this type of adaptation may come into play for some but not all moths under pest-control regimes using the tactic of pheromone-disruption, particularly those using high-dosage release technologies like pheromone rope dispensers or Microsprayers.