Epsilon Archive for Student Projects

Abstract

Cydia pomonella is a pest of several trees belonging to the family of Rosaceae but also of Juglans regia. Screening for volatiles attracting Cydia pomonella to Rosaceae spp. have been ongoing for years and has led to the discovery of pear ester as a potent host plant attractant. The origin of pear ester is suggested to be microbial, and yeasts from the genus of Metschnikowia has been shown to emit this volatile. In this pilot study we aim at identifying possible host plant cues, attracting Cydia pomonella to Juglans regia.
We sample volatiles from Cydia pomonella infested walnuts and from related larval frass, in addition we sample volatiles from microbes isolated from both infested nuts and frass, in the search for pear ester and a number of other key volatile compounds known from headspaces of Metschnikowia spp. with the ability to induce antennal response in Cydia pomonella. The selected key compounds are nonanal, decanal, 2-nonanone, 3-methylbutyl ethanoate, 2-phenylethanol, sulcatone, 3-methylbutyl propanoate and ethyl hexanoate.
Volatile collections are done with both dynamic- and static sampling methods and the samples are analysed using gas chromatography coupled with mass spectrometry. These methods proved sufficient in detecting all key compounds but pear ester, in the microbial- and frass headspaces. Continued sampling of microbial volatiles is needed, and based on this study, the recommended procedure going forward is dynamic headspace sampling. Other methods like community level metagenomics and DNA sequencing of individual microbes should also be considered, as well as adapting the inoculation time, temperature, and media to match the optimal conditions for pear ester emittance from Metschnikowia spp.