Attraction and Electroantennogram Responses of Male Mediterranean Fruit Fly to Volatile Chemicals from Persea, Litchi and Ficus Wood

Abstract

Trimedlure is the most effective male-targeted lure for the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). A similar response is elicited by plant substances that contain α-copaene, a naturally-occurring sesquiterpene. α-Copaene is a complex, highly-volatile, widely-distributed plant compound, and male C. capitata respond to material from both hosts (e.g., Litchi chinensis) and non-hosts (e.g., Ficus benjamina) that contain α-copaene. Avocado, Persea americana, recently was found to contain varying amounts of α-copaene in the bark and underlying cambial tissue. Short-range attraction bioassays and electroantennography (EAG) were used to quantify responses of sterile male C. capitata to samples of rasped wood from four avocado genotypes, L. chinensis, and F. benjamina. Gas chromatography-mass spectral (GC-MS) analysis was used to identify and quantify the major sesquiterpenes. Attraction and EAG amplitude were correlated, with L. chinensis eliciting the highest and F. benjamina the lowest responses. Responses to the avocado genotypes were intermediate, but varied among the four types. GC-MS identified 13 sesquiterpenes, including α-copaene, from all samples. Amounts of α-copaene in volatile collections from samples (3 g) ranged from 11.8 μg in L. chinensis to 0.09 μg in F. benjamina, which correlated with short-range attraction and EAG response. α-Copaene ranged from 8.0 to 0.8 μg in the avocado genotypes, but attraction and EAG responses were not correlated with the amount of α-copaene. Differences in enantiomeric structure of the α-copaene in the different genotypes and/or presence of additional sesquiterpenes may be responsible for the variation in male response. EAG responses were correlated with the amount of several other sesquiterpenes including α-humulene, and this compound elicited a strong antennal response when tested alone.