Search

The Chinese white pine beetle, Dendroctonus armandi Tsai & Li (Coleoptera: Curculionidae, Scolytinae), is considered the most destructive forest pest in the Qinling and Bashan Mountains of China. In recent years, winter temperature has dropped in these regions, and extremely low temperatures are hard to survive for insects. Cold hardiness becomes a crucial strategy because temperature change often leads to fluctuations in insect abundance, and the metabolism rate is a key index of resistance to cold in overwintering insects. Therefore, we investigated the relationship between the change in respiratory rate and the activity of metabolism‐related mitochondrial enzymes in D. armandi larvae under cold conditions. We found that the respiratory rate decreased, and it was matched with the activity of glutamate dehydrogenase, aconitase, and lipase during overwintering. Among the various test times under cold conditions, the respiratory rate also decreased with decreasing temperature and increased under very low temperatures. At all cold stress periods, glutamate dehydrogenase and lipase showed increased activity at higher temperatures and decreased activity under lower temperatures, but the activity of NAD‐malic enzyme, NADP‐malic enzyme, mitochondrial isocitrate dehydrogenase, and aconitase were contrary. Under all low temperatures, the activity of enzymes – except for NADP‐malic enzyme, glutamate dehydrogenase, and lipase – increased in short‐term cold stress and decreased in long‐term cold stress at 4, 0, −4, −6, −8, and −10 °C. However, at −2 °C, the activity of enzymes showed a decreasing trend in short‐term treatments and an increasing trend in long‐term treatments, except for mitochondrial isocitrate dehydrogenase. The results not only improve our understanding of the metabolic mechanism of cold adaptation in D. armandi, but also provide an important experimental basis for further study and biological pest control. [ABSTRACT FROM AUTHOR]

BACKGROUND: Insect pheromones and host volatiles are important for pest control due to their high efficiency and low potential for environmental pollution. The functions of myrtenol, myrtanol and myrtenal in pest–host interactions are unknown. This study aimed to determine the presence of myrtenol, myrtanol and myrtenal in newly emerged and emerged stages of Dendroctonus armandi, and in infected and healthy Pinus armandi, and to identify their roles in tree protection and pest management based on electroantennography (EAG), Y‐tube and toxicity experiments. RESULTS: Gas chromatographic and mass spectrometry (GC–MS) analyses, EAG, Y‐tube and toxicity assays revealed the following: (1) myrtenol was found in P. armandi phloem and did not exhibit significant toxicity towards D. armandi; (2) myrtanol was produced by infected P. armandi after D. armandi invasion and had significant toxicity towards D. armandi, especially females; and (3) myrtenal might represent an aggregation pheromone produced by female D. armandi to exert aggregation effects on other females, to help them overcome the resistance of P. armandi jointly and ensure a successful invasion, females remained in an aggregation state from leaving the host to mating in a new host. CONCLUSION: These findings suggest that myrtanol as a repellent has potential for the protection of P. armandi and that myrtenal could be used to trap and disorient D. armandi. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Bark beetles oxidize the defensive allelochemicals from their host trees to both detoxify and convert these materials into components of their pheromone system. The ability of this insect to adapt to its chemical environment might be explained by the action of major detoxification enzymes such as cytochrome P450s (or CYPs). Sixty-four sequences coding for P450s were identified, and most of the transcripts were found to be expressed in the larvae, pupae and adults of Dendroctonus armandi . To gain information on how these genes help D. armandi overcome the host defense, differential transcript levels of the CYP genes were observed between sexes and within the sexes. Significant differences were observed among developmental stages, in feeding on the phloem of Pinus armandi and in exposure to stimuli ((±)-α-pinene, (S)-(−)-α-pinene, (S)-(−)-β-pinene, (+)-3-carene, (±)-limonene and turpentine oil) for 8 h. We investigated the effect of sex and generations on the survivorship of individual D. armandi that were exposed to host volatiles at concentrations comparable to constitutive and induced levels of defense using fumigant exposure to understand the ability of the beetles to tolerate host defensive chemicals. The differential transcript accumulation patterns of CYP genes of these bark beetle provided insight into the ecological interactions of D. armandi with its host pine. [ABSTRACT FROM AUTHOR]

Simple Summary: The 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. [ABSTRACT FROM AUTHOR]