Tolerance, biochemistry and related gene expression in <i>Pagiophloeus tsushimanus</i> (Coleoptera: Curculionidae) exposed to chemical stress from headspace host‐plant volatiles

Abstract

Abstract Camphor, Cinnamomum camphora (L.) Presl, is used for mothproofing material due to its content of secondary metabolites. However, the phloem‐feeding weevil, Pagiophloeus tsushimanus (Coleoptera: Curculionidae), has been observed to feed exclusively on this plant without incurring apparent fitness costs. This phenomenon remains to be elucidated. Gas chromatography–mass spectrometry analysis of essential oil extracted from the phloem of camphor tree was performed. The top three components, all monoterpenoids, were eucalyptol (31.9%), D ‐camphor (19.2%) and linalool (10.2%), respectively. In headspace bioassays, both eggs and larvae showed the greatest sensitivity to eucalyptol, and there was a bell‐shaped relationship between the concentrations used and developmental time for eggs when exposed to D ‐camphor volatile. Exposure to essential oil mixture and D ‐camphor notably increased the activity of glutathione S‐transferase in the weevil. A corresponding short‐term induction of gene expression was also observed according to quantitative real‐time polymerase chain reaction analysis. In general, P. tsushimanus possessed various levels of tolerance to different host monoterpenoids. Over‐expression of glutathione S‐transferase in vivo probably relates to detoxification metabolism of these monoterpenoids. Our findings provide a valuable clue to understanding the mechanism underlying resistance to host‐specific chemical defences in this weevil pest.