Effect of varying proportions of the alcohol component on sex pheromone blend discrimination in male Oriental fruit moths

ABSTRACT. The flight response of individual male Oriental fruit moths, Grapholitha molesta (Busck), was observed in a sustained-flight tunnel to 100 blend–dosage combinations of the three sex pheromone components: (Z)- and (E)-8-dodecenyl acetate and (Z)-8-dodecen-l-ol (1, 3, 10, 30 and 100 μg of Z8-12: AC with, 2, 6, 10, 20% E and, 0, 3, 10, 30 or100% OH alcohol added). Complete flights to the source were observed only to blend combinations containing all three components. Males exhibited highest response levels to two dosages (3 and 10μg) of the natural 6% E blend and these levels were relatively unaffected by changes in the proportion of Z8-12: OH. Certain treatments surrounding the peak area also elicited high response levels compared to the 6% E treatments, but these were strongly dependent on the proportion of OH in the blend. Hierarchical cluster analysis was utilized to compare and group treatments that elicited similar levels of response over the entire flight sequence and to derive an area of blend-dosage combinations within the matrix tested that elicited peak levels of attraction. Analysis of the response patterns for suboptimal treatments adjacent to the area of optimal attraction showed that response specificity was controlled by two major effects on flight behaviour, one occurring early in the flight sequence affecting male orientation to the odour plume, and the other occurring later in the sequence as an arrestment of upwind flight. These effects were strongly influenced by changes in the OH component and the E isomer, with the latter playing the critical role in effecting flight behaviour. Temporal analysis of the flight response to treatments within the optimal area showed that whereas the % OH did not significantly affect the magnitude of response, increasing the level of Z8-12: OH in the blend did significantly increase the duration of each phase of the behavioural sequence. Considering both the magnitude and temporal aspects of male response, optimal attraction in male OFM was best characterized by a small area of treatments around the peak 6% E blends that contained 10% OH. Finally, field tests showed a high degree of correlation between trends in response with changing proportion of Z8-12: OH as observed in the flight tunnel. Peak dosages were generally higher in the field, however, compared to those in the flight tunnel.