Apple volatiles synergize the response of codling moth to pear ester

Codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae), is a major cosmopolitan pest of apple and other pome fruits. Ethyl (E,Z)-2,4-decadienoate (pear ester) has been identified as a host-derived kairomone for female and male codling moths. However, pear ester has not performed similarly in different fruit production areas in terms of the relative magnitude of moth catch, especially the proportion of females caught. Our work was undertaken to identify host volatiles from apples, and to investigate whether these volatiles can be used to enhance the efficacy of host kairomone pear ester for monitoring female and male codling moths. Volatiles from immature apple trees were collected in the field using dynamic headspace sampling during the active period of codling moth flight. Using gas chromatography-electroantennogram detector (GC/EAD) analysis, six compounds elicited responses from antennae of females. These compounds were identified by GC/mass spectrometry (MS) and comparisons to authentic standards as nonanal, (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, (Z,E)-α-farnesene, and (E,E)-α-farnesene. When the EAD-active compounds were tested individually in the field, no codling moths were caught except for a single male with decanal. However, addition of (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, or (E,E)-α-farnesene to pear ester in a binary mixture enhanced the efficacy of pear ester for attracting female codling moths compared to pear ester alone. Addition of the 6-component blend to the pear ester resulted in a significant increase in the number of males attracted, and enhanced the females captured compared to pear ester alone; the number of males and females caught was similar to that with the pear ester plus acetic acid combination lure. Our results demonstrate that it is possible to synergize the response of codling moth to host kairomone by using other host volatiles. The new apple-pear ester host kairomone blend should be helpful for monitoring female codling moth, and may provide the basis for further improvement of codling moth kairomone.