Expression Levels of Detoxification Enzyme Genes from Dendroctonus armandi (Coleoptera: Curculionidae) Fed on a Solid Diet Containing Pine Phloem and Terpenoids.

Lulu Dai,Haiming Gao,Hui Chen

doi:10.3390/insects12100926

Abstract

Simple SummaryThe bark beetle is the most well-known pest in coniferous trees worldwide. These insects only leave the host pine bark when they disperse to locate a new host. Determining how Dendroctonus armandi overcome the trees’ terpene-based defense systems has been the key problem in the study of bark beetles. Therefore, the aim of this study was to discover the molecular mechanism of insect detoxification enzymes’ ability to confer resistance to terpenes. For this purpose, the genes of cytochrome P450s, glutathione S-transferases, and carboxylesterases were studied in beetles given diets containing terpenes. The results suggest that beetles express different genes in response to terpenoids, and the responses of multiple detoxifying enzymes indicate these insects’ adaption to their chemical environment.Bark beetles overcome the toxic terpenoids produced by pine trees by both detoxifying and converting them into a pheromone system. Detoxification enzymes such as cytochrome P450s, glutathione S-transferases, and carboxylesterases are involved in the ability of Dendroctonus armandi to adapt to its chemical environment. Ten genes from these three major classes of detoxification enzymes were selected to study how these enzymes help D. armandi to respond to the host defenses. The expression profile of these detoxification enzyme genes was observed in adult beetles after feeding on different types of diet. Significant differences were observed between two types of seminatural diet containing the phloem of pines, and a purely artificial diet containing five monoterpenes ((−)-α-pinene, (−)-β-pinene, (+)-3-carene, (±)-limonene, and turpentine oil) also caused differential transcript levels in the detoxification enzyme genes. The results suggest that monoterpenes enter the beetles through different routes (i.e., respiratory and digestive systems) and cause the expression of different genes in response, which might be involved in pheromone metabolism. In addition, the xenobiotic metabolism in bark beetles should be considered as a system comprising multiple detoxifying enzymes.

Highlights

The Chinese white pine beetle (Dendroctonus armandi Tsai and Li (Coleoptera: Curculionidae)) is an aggressive species that attacks healthy Pinus armandii Franch., which is the principal pine species in the Qinling Mountain Forest region [1,2,3]
In this study, we evaluated the expression of detoxifying enzyme genes in Dendroctonus species, induced by diets containing host tree phloem
The specific response of P450 genes after feeding on host bark has been reported in other bark beetle species, such as Ips pini [39], I. paraconfusus [21], and D. ponderosae [33,40]

Summary

Introduction

The Chinese white pine beetle (Dendroctonus armandi Tsai and Li (Coleoptera: Curculionidae)) is an aggressive species that attacks healthy Pinus armandii Franch., which is the principal pine species in the Qinling Mountain Forest region [1,2,3]. Bark beetles only leave the host pine bark when they disperse to locate a new host. Bark beetles usually attack healthy trees with a disturbed terpenoid biosynthesis. Bark beetles must overcome the toxic terpenoids produced by the host pine during host colonization in order to maintain the beetle population [4]. The female beetles pioneer by boring through the healthy host and attracting males with sex pheromones to colonize and reproduce [1]. There is likely a special metabolic mechanism in bark beetles to overcome the chemical defense of healthy Chinese white pine, allowing this tree to be their specific host selection and explaining the different behavior between the sexes. Insecticides had never been used for this forest pest, so the host allelochemical was the primary pressure for Chinese white pine beetle

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