Location: Subtropical Horticulture Research
Title: Olfactory responses of male Medflies to plant material containing the parapheromone a-copaene Authors
Submitted to: International Symposium on Fruit Flies of Economic Importance Stellenbosh, South Africa
Publication Type: Abstract Only
Publication Acceptance Date: July 25, 2010
Publication Date: September 27, 2010
Citation: Niogret, J., Epsky, N.D., Montgomery, W.S., Kendra, P.E., Heath, R.R. 2010. Olfactory responses of male Medflies to plant material containing the parapheromone a-copaene. International Symposium on Fruit Flies of Economic Importance Stellenbosh, South Africa. p.302. Technical Abstract: The Mediterranean fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is a highly invasive species that is considered the most adaptable and polyphagous species of tephritid fruit fly due to its global distribution and its broad range of host plants, primarily tropical and subtropical fruits and vegetables. Ceratitis capitata is presently ranked first among economically important fruit fly pests, due to both damage to crops and costs of eradication. Trimedlure is a synthetic chemical that is highly attractive to male medflies and is the standard male-targeted lure used for this species. Medfly response to trimedlure is similar to response to the sesquiterpene a-copaene, a widely-distributed plant compound, and males respond to both host and non-host sources that contain a-copaene. Although a-copaene is reported to be 2 to 5 times more attractive than trimedlure, difficulties in obtaining synthetic a-copaene in sufficient quantities for large-scale trap deployment have prevented its use as a lure. As part of a study on sesquiterpene content of tree cambial tissue, we found that cambial (cambium+bark layers) tissue from avocado, Persea americana, contained a-copaene, and that levels were highly variable among different genotypes. Therefore, studies were initiated to determine if these sources of a-copaene were biologically active for male medflies. For comparative purposes, results were compared with responses to cambial tissue from Litchi chinensis and Ficus benjamina, two substrates known to elicit behavioral responses in male medflies. Behavioral bioassays and electroantennography (EAG) were used to evaluate responses of sterile male medflies; and GC-MS analysis was used to quantify the amounts of 13 sesquiterpenes, including a-copaene, common in cambial tissue from four avocado genotypes, from Litchi and from Ficus. Litchi elicited the highest response and Ficus the lowest response, with cambial tissue from the avocado genotypes eliciting intermediate responses that varied significantly among the four types in both the bioassays and EAG experiments. These responses, however, were not correlated with the amount of a-copaene, but were correlated with few other components like a-humulene, which triggered strong antennal responses in EAG. Additional sesquiterpenes may be responsible for the high responses observed with the low a-copaene substrates. Identification of these chemicals may provide a new understanding of the biological basis for the response of male medflies to these wood sources, which could lead to development of new tools for improved detection and control. Attractiveness of a-humulene still has to be tested in bioassays but, this compound triggered a strong antennal response of the male medflies. Although not necessarily attractive, this compound may play a synergetic role to a-copaene for C. capitata attraction.