Abstract: 【Aim】This study aims to preliminarily clarify the joint action mechanism of ethyl formate (EF) and methyl isothiocyanate (MITC) to Acanthoscelides obtectus through analyzing the transcriptome data of A. obtectus fumigated with EF, MITC and EF+MITC.【Methods】The A. obtectus adults were treated with fumigation of EF(22.398 μL/L), MITC(0.854 μL/L) and EF+MITC(14.764 μL/L) through wild-mouth bottle fumigation method. The control group (CK) was not fumigated. Transcriptome sequencing of the A. obtectus adults treated with fumigation of EF, MITC and EF+MITC was performed with Illumina Hi Seq^TM 4000 sequencing platform. GO classification and KEGG enrichment analysis were performed on differentially expressed genes (DEGs). Six DEGs were selected for RT-qPCR validation.【Results】 There were 171 and 293 DEGs in the CK vs EF and CK vs MITC comparative groups, respectively, and most of them were up-regulated. However, the number of DEGs in the CK vs EF+MITC comparative group was 1 745, and most of them were down-regulated. GO classification of DEGs showed that DEGs in the  CK vs EF and CK vs MITC comparative groups were mainly enriched in cellular anatomical entity, binding, and catalytic activity, while those in the CK vs EF+MITC comparative group were mainly enriched in cellular anatomical entity, binding, and cellular process. KEGG pathway enrichment analysis of DEGs showed that DEGs in the CK vs EF comparative group were mainly enriched in pathways of protein digestion and absorption, lysosome and protein processing in endoplasmic reticulum, those in the CK vs MITC comparative group were mainly enriched in pathways of focal adhesion, ECM-receptor interaction and insect hormone biosynthesis, and those in the CK vs EF+MITC comparative group were mainly enriched in RNA transport, DNA replication and mismatch repair. In addition, the expression levels of two and three detoxification enzyme genes in A. obtectus adults in response to EF and MITC fumigation treatments were significantly down-regulated, respectively, however, the expression levels of five detoxification enzyme genes in A. obtectus adults in response to EF+MITC fumigation treatment were significantly down-regulated as compared with those in the CK. The expression trends of the six selected DEGs were basically consistent with the transcriptome data.【Conclusion】The results of this study indicate that the combination of EF and MITC has a synergistic effect, which can induce cell genotoxic damage in A. obtectus. The inhibition of expression of detoxification enzyme genes seems to be the main reason for its synergistic effects. In this study, the molecular mechanism of fumigation and insecticidal effect of the mixture of EF and MITC on A. obtectus was preliminarily clarified, which provides an important basis for the further study on the combined action mechanism of EF and MITC on A. obtectus.

Key words: Acanthoscelides obtectus, ethyl formate, methyl isothiocyanate, mixture, transcriptome