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.

<I>Xyleborus glabratus</I>, <I>X. affinis</I>, and <I>X. ferrugineus</I> (Coleoptera: Curculionidae: Scolytinae): Electroantennogram Responses to Host-Based Attractants and Temporal Patterns in Host-Seeking Flight

“…ax/(b ϩ x), where x represents the substrate dose in milliliters of saturated vapor, y represents the normalized EAG response, and the coefÞcients a and b represent maximum EAG response and receptor binding afÞnity, respectively. Hyperbolic equations commonly are used for ligand-binding studies, and have been shown previously to serve well for characterization of EAG doseÐresponse relationships in insects (Kendra et al 2008(Kendra et al , 2009Niogret et al 2011b;Jenkins et al 2012). The EAG regression equations were as follows: manuka oil lure: y ϭ 77.42x/(0.74 ϩ x), R 2 ϭ 0.986; phoebe oil lure: y ϭ 106.15x/(0.96 ϩ x), R 2 ϭ 0.979; and silkbay wood volatiles: y ϭ 105.93x/(0.61 ϩ x), R 2 ϭ 0.982.…”

“…IdentiÞcation of ethanol as a standard reference compound for Xyleborus species permitted normalization of EAG responses and comparative analyses of olfaction, as has been done with other pest insects (Kendra et al 2008(Kendra et al , 2009Niogret et al 2011b;Jenkins et al 2012). Aside from the difÞculties with dissection and manipulation of such small antennae, the main drawback was that the excised antennae were viable for only Ϸ30 min, necessitating short EAG recording sessions.…”

“…Test substrates for EAG analyses consisted of ethanol (5-ml ethyl alcohol 95%; Pharmco-Aaper, BrookÞeld, CT); manuka oil lures (Synergy Semiochemicals); phoebe oil lures (Synergy Semiochemicals); and silkbay wood (12-g freshlyrasped bark and cambium, collected at Archbold Biological Station, prepared as reported in Niogret et al 2011b). Each substrate was placed into a 250-ml hermetic glass bottle Þtted with a septum port lid, and allowed a 2-h equilibration time for headspace saturation at 24ЊC.…”

“…Olfactory responses were recorded with a Syntech EAG system (Syntech, Hilversum, the Netherlands), which included a micromanipulator assembly (MP-15), a data acquisition interface box (serial IDAC-232), a stimulus air controller (CS-05), and EAG 2000 software. Initial attempts were made with glass micropipette electrodes, silver wire electrodes, and whole head mounts, a standard method used in our laboratory for EAG recordings from other insects (Kendra et al 2005(Kendra et al , 2008Niogret et al 2011b); however, this method proved unsuccessful for Xyleborus because of periodic twitching of antennal muscles and movement of mouthparts. Multiple variations of this micropipette method also were evaluated (e.g., using partial head mounts, single excised antenna, multiple antennae, bare silver wire electrode at tip of antenna), but none were able to achieve a satisfactory baseline nor strong antennal signal in our target species, despite published reports of micropipette EAG recordings obtained from bark beetles (e.g., Dendroctonus and Ips spp.…”

Plant Odors as Fruit Fly Attractants

“…Male C. capitata respond to material from both hosts (e.g., Litchi chinensis Sonn.) and non-hosts (e.g., Ficus benjamina L.) that contain α-copaene (Warthen and McInnis 1989;Niogret et al 2011). While α-copaene is reported to be 2-5 times more attractive than trimedlure, difficulties in obtaining this compound in quantities sufficient for large scale trap deployment have prevented its use as a field lure (Cunningham 1989).…”