The ability of the bacteria Bacillus thuringiensis (Bt) to effectively kill target insects is well-established. However, the mechanisms by which Bt interacts with gut microbes to trigger insect cell death is in forest pests remain unclear. Dioryctria abietella is one of the most destructive forest pests for coniferous trees. In the present work, D. abietella was used as a model to investigate the effects of Bacillus thuringiensis subsp. galleriae 05041 strain (Bt05041, 1 x 108 CFU mL-1) on the gut microbiota and midgut cells at different time points after treatment (3, 6, 9, 12, and 24 h). Treatment with Bt05041 significantly enriched the gut bacterial community, altered the composition of the gut microbiota, and resulted in the dysfunction of gut cells. Bt05041 treatment significantly increased the OTUs (operational taxonomic units) compared to the number in the control group. The genera Enterococcus, Wolbachia, Bacillus, and unclassified Enterobacteriaceae had relatively high abundances after Bt05041 treatment. The midgut cells of D. abietella deteriorated significantly in response to Bt05041, as determined by transmission electron microscopy. Changes in cell morphology included the disruption of microvilli, deformation of organelles, and cytoplasmic vacuolation. With the extension of the Bt05041 treatment duration, the basal plasma membrane and septate junction gradually ruptured until cells were completely dissolved. In conclusion, our findings reveal the effects of Bt05041 exposure for various durations on gut microbes and cells, clarify the detailed mechanism underlying Bt-mediated apoptosis, and provide new insights into the use of Bt for forest pest control.

The poplar and willow weevil , Cryptorhynchus lapathi L., a major universally destructive wood-boring insect has become one of the important quarantine pests that is extremely destructive to forestry development and needs to be controlled. Entomopathogenic fungi (EPF) are considered safe and friendly for humans and the environment and play important roles in controlling insect pest populations. In this study, the screening of entomopathogenic fungi for control of C. lapathi is reported through the evaluation of virulence of four fungal Beauveria bassiana (CFCC81428, CFCC83116, CFCC83486, CFCC87297) strains, one B. brongniartii (CFCC83487) strain and one Metarhizium anisopliae (CFCC88953) strain. The virulence of the different strains was appraised by correct mortality rate, cumulative mortality rate, median lethal concentration (LC 50 ) and median lethal time (LT 50 ). B. bassiana strains CFCC81428 and CFCC83116 were the most virulent among the six strains with a mortality up to 100%, and the LT 50 were 2.7 and 3.1 days. Five conidia concentrations of three strains (CFCC81428, CFCC83116 and CFCC87298) that caused high virulence was screened for dose-relationship. Their effect on controlling C. lapathi larvae were also determined under field condition by brushing conidia suspensions on C. lapathi larvae infested in a poplar trunk. The cumulative rate in the field was lower than those obtained from the laboratory, but the order of the virulence of different strains did not change. Mortality in all three strains occurred at their highest concentration (1.0 × 10 8 conidia mL −1 ). Under field conditions, the CFCC81428 strain was the most effective, causing mortalities of 80.3% and 75.2% in two plots in Beipiao and Lindian counties, respectively, followed by CFCC83116 (69.1%, 66.6%) and CFCC87298 (60.7%, 59.3%). Based on our results, the B. bassiana strain CFCC81428 has the potential as a biological insecticide to control C. lapathi larvae.

Dioryctria abietella is a major pest of conifer cones that can initiate specific behaviours (locating hosts, finding mates and selecting oviposition sites) through sensitive olfactory systems. General odorant‐binding proteins are involved in the first step in odorant perception in insects, but their specific functional roles in D. abietella chemoreception have not been fully elucidated. In this study, quantitative real‐time polymerase chain reaction (PCR) examinations showed that DabiGOBP2 is predominantly expressed in the antennae of female adults. Western blot experiments further confirmed that these proteins show biased expression in the tissues. Binding property analysis demonstrated that DabiGOBP2 exhibited ligand specificity to terpenes, especially myrcene (Ki = 8.19 ± 0.05). Electroantennogram (EAG) and Y‐tube assays showed that three plant volatiles elicited high EAG responses, but only dodecanal showed a strong attraction to females. However, myrcene and isobutyl benzoate were significantly repellent to males at high doses in the behaviour test. In conclusion, exploring the functions of DabiGOBP2 can help in better understanding the mechanism of the olfactory system of D. abietella and developing novel strategies to control this pest.

The coneworm Dioryctria abietella (Lepidoptera: Pyralidae) is an economy devastating pest that infests many valuable conifer species in the Holarctic regions, such as Pinus koraiensis Siebold and Zucc. The chemosensory system plays a crucial role in the mating, foraging, and ovipositing of this pest, and therefore it is desirable to identify chemosensory molecules for pest control. However, little is known at molecular level about the olfactory mechanisms in D. abietella. In the present study, we first established antennal transcriptomes of D. abietella and identified 132 putative chemosensory genes, including 15 odorant-binding proteins, 18 chemosensory proteins, 65 odorant receptors, 5 sensory neuron membrane proteins, 24 ionotropic receptors, and 5 gustatory receptors. In addition, phylogenetic trees were constructed for chemosensory genes to investigate the orthologs between D. abietella and other species of insects. Furthermore, we also compared the patterns of motifs between OBPs and CSPs using MEME. Additionally, we observed that most of DabiOBPs and DabiCSPs had the antenna-biased expression by quantitative real-time PCR (RT-qPCR), and there was a higher expression of DabiPBP1 and DabiPBP2 in male antennae than in female antennae. The binding sites of DabiPBPs (DabiPBP1, DabiPBP2) and DabiPRs (DabiOR19, DabiOR31) to the sex pheromone were predicted well by three-dimensional docking structure modelling and molecular docking. Our finding supplied a foundation for further research on the binding process of OBPs or CSPs and sensing process of ORs, SNMPs, IRs or GRs in D. abietella.

Dioryctria abietella is a coniferous seed orchard pest that can damage a series of host plants and cause huge losses to the forest economy. Sex pheromones play an important role in lepidopteran sex communication for reproduction and can be used as biological control agents to monitor and trap pests. However, the genes involved in the biosynthesis, transportation, and degradation of D. abietella sex pheromones have not been studied extensively. Transcriptome analysis of female D. abietella sex pheromone glands (PGs) revealed that 210 candidate genes might be involved in sex pheromone biosynthesis (139 genes) and chemoreception systems (71 genes). The gene expression patterns exhibited four desaturase genes (DabiDES4-7) and one fatty acid reductase gene (DabiFAR6), which were more highly expressed in sex pheromone glands than in other tissues, suggesting that these enzymes play an important role in D. abietella sex pheromone synthesis. In addition, most DabiOBPs showed high expression in antennae, but only DabiOBP4 exhibited specific expression in sex pheromone glands, suggesting that they may play many physiological roles in D. abietella. We put forth a reasonable hypothesis about type I pheromone biosynthesis pathways based on these genes identified in the D. abietella sex pheromone gland transcriptome. Our findings lay a foundation for population monitoring, mating disruption, mass trapping, and the development of ecologically acceptable management strategies.