Sexual dimorphism in the olfactory orientation of adult Cydia pomonella inresponse to alpha-farnesene

The role of host plant-derived volatile substances on the behaviour of adul t codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae) is poorly und erstood. We tested the response of females and males to a range of alpha-fa rnesene dosages. Natural alpha-farnesene from apples contains the E,E and Z ,E isomers in varying proportions. No difference in the response of C. pomo nella to preparations containing two different proportions of the E,E and Z ,E isomers was noted (77:20.7 or 1.2:84.7% E,E and Z,E isomers respectively ), indicating a similar bioactivity of E,E and Z,E alpha-farnesene on codli ng moth. A marked sexual dimorphism was found to increasing dosages of alph a-farnesene. Females were attracted to low dosages (starting from 63.4 ng) and repelled by high dosages (ending at 12 688 ng). The dose response over this concentration range was linear with a negative slope. Both mated and v irgin females responded similarly in kind but differently in degree, both a ttraction and repellency being more pronounced in mated females. Males were neither attracted nor repelled over a large dose range (63.4 to 12 688 ng) except the highest rate which was attractive. This indicates a stronger de pendency of females on plant-derived volatiles.