Omics of the Emerald Ash Borer During Interaction with Ash

The emerald ash borer (EAB), Agrilus planipennis Fairmaire is a recently introduced invasive insect pest of ash, Fraxinus spp. in North America (NA). Its invasion has had significant economic and ecological impact on urban and forest ecosystems and continues to do so. Relative to its resistant Asian host, which are attacked when stressed, this pest threatens the existence of all NA ash species. EAB larvae feed on phloem and kill trees in 3-4 years post infestation. To date relatively little is known at the molecular level on invasive buprestid beetles that are of significant importance. To decipher the survival strategies of EAB larvae, global gene expression analyses through RNA-seq was performed on the midgut tissue of larvae feeding on susceptible NA ash (F. pennsylvanica, green ash) and resistant Asian ash (F. mandschurica, Manchurian ash). Approximately 55,000 high quality expressed sequence tags (ESTs) were obtained and using the R-based statistical package Deseq, 380 genes were found to be differentially expressed (265 up-regulated and 114 down-regulated) between the larval samples described above. Molecular functions including digestion, detoxification and transport were up-regulated in larvae feeding on green ash suggesting their possible role in adaptation. The observed RNA-Seq profiles were confirmed by quantitative PCR and on-going metabolomic studies are providing new insights into the metabolism of potential host factors. These results are unique to a buprestid beetle that has had a significant impact on the NA ecosystem; and thus will provide the basis to learn the adaptation criteria required for an invasive insect.