Inter-laboratory comparison of plant volatile analyses in the light of intra-specific chemodiversity.

INTRODUCTION: Assessing intraspecific variation in plant volatile organic compounds (VOCs) involves pitfalls that may bias biological interpretation, particularly when several laboratories collaborate on joint projects. Comparative, inter-laboratory ring trials can inform on the reproducibility of such analyses. OBJECTIVES: In a ring trial involving five laboratories, we investigated the reproducibility of VOC collections with polydimethylsiloxane (PDMS) and analyses by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). As model plant we used Tanacetum vulgare, which shows a remarkable diversity in terpenoids, forming so-called chemotypes. We performed our ring-trial with two chemotypes to examine the sources of technical variation in plant VOC measurements during pre-analytical, analytical, and post-analytical steps. METHODS: Monoclonal root cuttings were generated in one laboratory and distributed to five laboratories, in which plants were grown under laboratory-specific conditions. VOCs were collected on PDMS tubes from all plants before and after a jasmonic acid (JA) treatment. Thereafter, each laboratory (donors) sent a subset of tubes to four of the other laboratories (recipients), which performed TD-GC-MS with their own established procedures. RESULTS: Chemotype-specific differences in VOC profiles were detected but with an overall high variation both across donor and recipient laboratories. JA-induced changes in VOC profiles were not reproducible. Laboratory-specific growth conditions led to phenotypic variation that affected the resulting VOC profiles. CONCLUSION: Our ring trial shows that despite large efforts to standardise each VOC measurement step, the outcomes differed both qualitatively and quantitatively. Our results reveal sources of variation in plant VOC research and may help to avoid systematic errors in similar experiments.

Two new species of the bee-mimicking genus Mallophora (Diptera, Asilidae) from Colombia.

Mallophora Macquart, 1834 is a bee-mimicking genus of Asilidae, which has more than 50 described species in the Neotropical Region. Examination of specimens of this genus from Colombia indicate that there are two undescribed species based on the structure of the hind leg of males. Here we describe Mallophora gauteovan sp. nov. and Mallophora kalos sp. nov. from Tayrona National Park (Magdalena) and Arauca, respectively. For each new species a diagnosis and a description including the structure of the face, thorax, male hind leg, abdomen, and hypandrium are provided. All morphological structures are documented with digital photographs.