Transcriptome profiling and RNA interference reveals relevant detoxification genes in Monochamus alternatus response to (+)‐α‐pinene.

Understanding the mechanism of insect resistance to toxic effects of phytochemicals can provide an insight into plant–herbivore interactions. Monochamus alternatus Hope, a main vector of pine wood nematode (Bursaphelenchus xylophilus), prefers to infest masson pine (Pinus massoniana Lamb) and causes huge economic and environmental losses. α‐Pinene is the primary component of resin produced by masson pine and plays a crucial role in defending against herbivorous insects, but its defensive effects on M. alternatus larvae are barely known. Here, we explored the physiological metabolism in M. alternatus larvae that were fumigated with (+)‐α‐pinene, (‐)‐α‐pinene, β‐pinene, (R)‐(+)‐limonene, myrcene and (‐)‐α‐phellandrene. (+)‐α‐Pinene showed the highest fumigant toxicity to M. alternatus larvae among these monoterpenes, and the fourth instar larvae possessed the highest resistance to this compound at the larval stage. Comparative transcriptome analysis detected 423 up‐regulated and 311 down‐regulated genes in the larvae fumigated with (+)‐α‐pinene, which were mainly related to detoxification, energy and protein metabolism. Among the differentially expressed genes encoding for detoxification enzymes, 14 P450s, 13 UGTs, 1GSTs and 3ABCs were dramatically up‐regulated in the larvae fumigated with (+)‐α‐pinene. Silencing of P450s via RNA interference led to an increased mortality in the larval fumigated with (+)‐α‐pinene. Piperonyl butoxide exposure significantly increased the mortality and inhibited the expressions of P450s, UGTs and ABCs in the larvae fumigated with (+)‐α‐pinene. These results suggested an important role of P450s in the resistance of M. alternatus larvae to (+)‐α‐pinene fumigation, which may facilitate the understanding of terpenoid detoxification in M. alternatus larvae. [ABSTRACT FROM AUTHOR]