Cradle for the newborn Monochamus saltuarius: Microbial associates to ward off entomopathogens and disarm plant defense

Emerald Ash Borer Infestation-Induced Elevated Negative Correlations and Core Genera Shift in the Endophyte Community of Fraxinus bungeana

Endophytes, prevalent in plants, mediate plant-insect interactions. Nevertheless, our understanding of the key members of endophyte communities involved in inhibiting or assisting EAB infestation remains limited. Employing ITS and 16S rRNA high-throughput sequencing, along with network analysis techniques, we conducted a comprehensive investigation into the reaction of endophytic fungi and bacteria within F. bungeana phloem by comparing EAB-infested and uninfected samples. Our findings reveal that EAB infestation significantly impacts the endophytic communities, altering both their diversity and overall structure. Interestingly, both endophytic fungi and bacteria exhibited distinct patterns in response to the infestation. For instance, in the EAB-infested phloem, the fungi abundance remained unchanged, but diversity decreased significantly. Conversely, bacterial abundance increased, without significant diversity changes. The fungi community structure altered significantly, which was not observed in bacteria. The bacterial composition in the infested phloem underwent significant changes, characterized by a substantial decrease in beneficial species abundance, whereas the fungal composition remained largely unaffected. In network analysis, the endophytes in infested phloem exhibited a modular topology, demonstrating greater complexity due to an augmented number of network nodes, elevated negative correlations, and a core genera shift compared to those observed in healthy phloem. Our findings increase understanding of plant-insect-microorganism relationships, crucial for pest control, considering endophytic roles in plant defense.

Unveiling winter survival strategies: physiological and metabolic responses to cold stress of Monochamus saltuarius larvae during overwintering

BACKGROUND

Monochamus saltuarius is a destructive trunk-borer of pine forest and an effective dispersal vector for pinewood nematode (PWN), a causative agent of pine wilt disease (PWD), which leads to major ecological disasters. Cold winter temperatures determine insect survival and distribution. However, little is known about the cold tolerance and potential physiological mechanisms of M. saltuarius.

RESULTS

We demonstrated that dead Pinus koraiensis trunks do not provide larvae with insulation. The M. saltuarius larvae are freeze-tolerant species. Unlike most other freeze-tolerant insects, they can actively freeze extracellular fluid at higher subzero temperatures by increasing their supercooling points. The main energy sources for larvae overwintering are glycogen and the mid-late switch to lipid. The water balance showed a decrease in free and an increase in bound water of small magnitude. Cold stress promoted lipid peroxidation, thus activating the antioxidant system to prevent cold-induced oxidative damage. We found eight main pathways linked to cold stress and 39 important metabolites, ten of which are cryoprotectants, including maltose, UDP-glucose, d-fructose 6P, galactinol, dulcitol, inositol, sorbitol, l-methionine, sarcosine, and d-proline. The M. saltuarius larvae engage in a dual respiration process involving both anaerobic and aerobic pathways when their bodily fluids freeze. Cysteine and methionine metabolism, as well as alanine, aspartate, and glutamate metabolism, are the most important pathways linked to antioxidation and energy production.

CONCLUSIONS

The implications of our findings may help strengthen and supplement the management strategies for monitoring, quarantine, and control of this pest, thereby contributing to controlling the further spread of PWD. © 2024 Society of Chemical Industry.

Identification of Attractants from Three Host Plants and How to Improve Attractiveness of Plant Volatiles for Monochamus saltuarius

As a new vector insect of pine wood nematodes in China, the Monochamus saltuarius (Coleoptera: Cerambycidae) vectors pine wilt nematodes into healthy pine trees through feeding and oviposition, resulting in huge economic losses to forestry. A promising control strategy is to develop safe and efficient attractants. This study aims to screen for the key active volatiles of Pinus koraiensis (Pinales: Pinaceae), Pinus tabuliformis (Pinales: Pinaceae), and Picea asperata (Pinales: Pinaceae) that can attract M. saltuarius, and to study the synergistic attraction of the main attractant plant volatiles with ethanol and insect aggregation pheromones. The preference of M. saltuarius for three hosts is P. koraiensis > P. tabuliformis > Picea asperata. We detected 18 organic volatiles from three host plants. Through EAG assays and indoor Y-tube behavioral experiments, 3-carene, (-)-camphor, β-pinene, α-phellandrene, terpinolene, α-pinene, D-limonene, and myrcene were screened to have attractive effects on M. saltuarius. We found that 3-carene, β-pinene, and α-pinene are the most attractive kairomones in field experiments, which may play a crucial role in the host localization of M. saltuarius. Ethanol has a synergistic effect on the attractant activity of 3-carene and β-pinene, and the synergistic effect on β-pinene is the best. The mixture of ethanol, 2-undecyloxy-1-ethanol, and ipsdienol can significantly enhance the attraction effect of β-pinene on M. saltuarius. These new findings provide a theoretical basis for the development of attractants for adult M. saltuarius and contribute to the green control of M. saltuarius.

Comparative metatranscriptomics reveals effect of host plant on microbiota gene expression of Anastrepha obliqua (Diptera: Tephritidae) larvae

The microbiota associated with phytophagous insects perform several functions that help insects exploit plant resources. Thus, microorganisms contribute to the dispersal of phytophagous species to new host plants, thereby promoting diversification. In this study, metatranscriptomic analysis was used to compare the gene expression of the microbiome of Anastrepha obliqua Macquart larvae feeding on 3 of its host plants: Spondias purpurea L (red mombin), Mangifera indica L (mango), and Averrhoa carambola L (starfruit). To identify differential gene expression in relation to the host plant, transcript abundance was compared. The results of the taxonomic and functional beta-diversity analysis showed that there were significant differences in the structures and activities of the microbial communities depending on the infested plant. Among the microorganisms, bacteria and fungi were active components of the microbiota. Differential expression analyses showed that the different active genes in each of the plants analyzed were mainly grouped into categories related to carbohydrate and amino acid metabolism, with some of these genes coding for cytochrome o ubiquinol oxidase, cytochrome c, and the enzyme isocitrate dehydrogenase. The microbiota of A. carambola larvae differed more at the level of community structure and gene function, possibly due to the different nutritional composition of the A. carambola and the presence of a set of secondary metabolites specific to the family Oxalidaceae. In conclusion, the transcriptional activity of the microbiota of A. obliqua larvae is influenced by diet, which is important because it could influence the performance of the insect on each of its different host plants.

Host-plant adaptation in xylophagous insect-microbiome systems: Contributionsof longicorns and gut symbionts revealed by parallel metatranscriptome

Adaptation to host plants is of great significance in the ecology of xylophagous insects. The specific adaptation to woody tissues is made possible through microbial symbionts. We investigated the potential roles of detoxification, lignocellulose degradation, and nutrient supplementation of Monochamus saltuarius and its gut symbionts in host plant adaptation using metatranscriptome. The gut microbial community structure of M. saltuarius that fed on the two plant species were found to be different. Plant compound detoxification and lignocellulose degradation genes have been identified in both beetles and gut symbionts. Most differentially expressed genes associated with host plant adaptations were up-regulated in larvae fed on the less suitable host (Pinus tabuliformis) compared to larvae fed on the suitable host (Pinus koraiensis). Our findings indicated that M. saltuarius and its gut microbes respond to plant secondary substances through systematic transcriptome responses, allowing them to adapt to unsuitable host plants.