Abstract
Solid-phase micro-extraction (SPME) fibres and automated thermal desorption (ATD) tubes were used with gas chromatography-mass spectrometry (GC-MS), to investigate volatile secretions from the headspace gas of adults and larvae of confused flour beetle Tribolium confusum du Val, saw-toothed grain beetle Oryzaephilus surinamensis (L.), grain weevil Sitophilus granarius (L.), flour mite Acarus siro L. and storage mite Glycyphagus domesticus (De Geer). A number of VOCs were specifically linked with confused flour beetle T. confusum and not observed with the other insect and mite species. For instance, 2-methyl-p-benzoquinone and 2-ethyl-p-benzoquinone were specifically linked to confused flour beetle. However, this study found that benzoquinones were not present in the headspace volatiles of the larvae of confused flour beetle, whereas, 1-pentadecene was detected in adults and larvae of confused flour beetle. The results of the volatile extraction experiments with saw-toothed grain beetles O. surinamensis showed that several volatiles were detected in the adults and larvae of saw-toothed grain beetle but not in the other insect and mite species. Some of these VOCs were detected only in adults, and these were butanoic acid, 1-methylethyl ester and 1,3-octadiene. The others were found in both larvae and adults. These were 2,4-hexadien-1-ol, octane, 3-methylbutanoic acid, 2,5-dimethylpyrazine, 1-octen-3-one and 1-octen-3-ol. The analysis of the headspace from grain weevil S. granarius showed three VOCs which were specifically linked to weevils compared to the other species. These were mequinol, 2-methylpropanoic acid and 2-pentanone. The results showed that the known mite-produced alarm pheromone citral (comprising (Z)-3,7-dimethyl-2,6-octadienal and (E)-3,7-dimethyl-2,6-octadienal) was detected in both mite species flour mite A. siro and storage mite G. domesticus but not in insect species. This study has identified a number of VOCs which may enable the early detection of storage insects and mites in grain stores. Many of the VOCs identified were specific to either mites or one of the insect species studied which could enable specific identification of the cause of infestation.