A potential detection method is to analyze the air

A potential detection method is to analyze the air within a grain mass for specific volatile compounds (VOCs) released by insects. In recent years, headspace solid phase microextraction (HS-SPME) in conjunction with gas chromatography–mass spectrometry (GC–MS) has been employed to examine volatile compounds from stored product insects in grain [10]. It has been widely used to isolate and identify the VOCs of stored grain and has also been used to detect the aggregation pheromone and other volatile metabolites of the lesser grain borer Rhyzopertha dominica (F.) and T. castaneum[11]. SPME–GCMS has also been used to determine ongoing spoilage based on the production of unique VOCs by insects to communicate with their own species [12]. Based on previous studies [13], the goal of this study was to screen samples of healthy (non-insect-contaminated) flour, samples of T. castaneum adults and samples of flour infested with T. castaneum adults using a non-polar column at 25°C to establish if there were clearly identifiable compounds unique to flour alone, infested flour and the contaminating insects, which would indicate that HS-SPME–GCMS could be used as a way of identifying an infestation of T. castaneum in flour. If this were the case, this technique might also be used to gauge the quality of stored products.
Materials and methods
Results <br> Discussion Senthilkumar et al. [14] were the first to detect 1-tridecene from T. castaneum. They speculated that this Adriamycin HCl was a sex pheromone of the species in accordance with a study of male Parastizopus transgariepinus (Koch) by Geiselhardt et al. [15]. While1-tridecene was detected in the current study, two other previously reported volatiles, methyl-1,4-benzoquinone and ethyl-1,4-benzoquinone were not. These compounds were considered to be defensive secretions [12]. However, 2-methyl-p-benzoquinone and 4-ethyl-1,3-benzanediolwere detected for the first time under the current experiment conditions. Nonanal has also been identified in healthy flour by Maeda et al. [3]. The major VOCs in descending order of response level were hexanal, hexane, D-limonene, pentanal and 2-pentyl-furan. Again, 2-heptanone and heptanal have previously been detected in T. castaneum infested flour and hexanal has been detected in both flour and T. castaneum infested flour [3]. However, some compounds like heptane, pentanal and decamethyl-cyclopentasiloxane were identified for the first time in the present study. The quantity of the 21 compounds found in the samples of flour alone and T. castaneum infested flour were almost same. This suggests that the presence of T. castaneum has little impact on the VOCs of flour. Most compounds from flour and T. castaneum were different. Hexane was the only compound that could be detected from all of three samples, but it was found at a very low level in T. castaneum. Most compounds found in healthy flour were detected in T. castaneum infested flour. On the other hand, just a few compounds found from T. castaneum alone could be detected in T. castaneum infested flour. There were some specific compounds that were only detected in T. castaneum infested flour. The common peak in the spectra of healthy flour and T. castaneum infested flour was hexane, so the data for them in Table 1 were scaled relative to hexane for comparison. The equivalent levels of 2-ethyl-2,5-cyclohexadiene-1,4-dione in T. castaneum and Flour with T. castaneum could be a compound to determine T. castaneum infestations in flour (Table 1). For T. castaneum, 2-methyl-p-benzoquinonewas used as a scale for comparison.
Conclusion Totally, 71 different compounds were identified in flour, T. castaneum and T. castaneum infested flour use HS-SPME coupled with GC–MS technique. However, most of compounds from T. castaneum infested flour are same as healthy flour. The compound 2-ethyl-2,5-cyclohexadiene-1,4-dione was only found in T. castaneum infested flour (e.g. it is listed in Fig. 4 and Table 1). This suggests that 2-ethyl-2,5-cyclohexadiene-1,4-dione is considered to be a very useful VOC for detecting T. castaneum in flour.