Evaluation of trimedlure dispensers by a method based on thermal desorption coupled with gas chromatography-mass spectrometry

Knowledge about the behaviour of trimedlure (TML) dispensers is essential to ensure the efficacy of monitoring and control methods based on TML as attractant. There are several commercially available TML dispensers, and each of them has a different useful life and TML release profile. Their emission is also affected differently by environmental factors. Even the same type of dispenser sometimes shows an important variability in the TML release rate. Because of the importance of methods based on TML lures in the control of the Mediterranean fruit fly and the influence of the TML dispenser on the efficacy of these control methods, we developed a non-destructive flow-through system to measure the TML release rate. This volatile collection method (VCM) adsorbs TML vapour on a Tenax TA desorption tube, and TML is quantified by Thermal desorption coupled with gas chromatography/mass spectrometry. Two types of TML dispensers, a polymeric (Aralure) and a mesoporous (Epalure), were field aged during 3 months. The TML release rates of these dispensers were determined by both, VCM and solvent extraction method. In this study, the correlation between both measurement methods is shown. A field trial has also been carried out to correlate trap catches and TML emission of each type of tested dispenser. The VCM allows a quick and accurate evaluation of the current behaviour of commercial dispensers along their useful life. It also allows comparing the TML release rate between different dispensers. We believe that the VCM can be useful for dispenser manufacturers to determine seasonal dispenser performance before a new product is introduced in the market, and to rapidly verify TML dispenser release when field-aged dispenser efficacy is in question. Thus, it can be employed as a quality control of commercial dispensers.