Midgut-specific profiles of the emerald ash borer larvae (Agrilus planipennis Fairmaire)

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 continues to have significant economic and ecological impact on urban and forest ecosystems. Compared to its Asian host, which are attacked when stressed, this pest attacks healthy NA ash species. The larval stages of EAB feed on phloem and kill trees in 3-4 years post infestation. To decipher the survival strategies of EAB larvae on NA ash species, global gene expression analyses through RNA-Seq was performed on the midgut tissue of larvae feeding on susceptible NA green ash (F. pennsylvanica) and resistant Asian Manchurian ash (F. mandschurica). 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 (266 upregulated and 114 down regulated) between the larval samples described above.  Among these differentially expressed genes, a subset of them linked to molecular function (catalytic activity, transporter activity and response to stress) and those involved in dealing with plant toxins were upregulated in larvae reared on green ash. The observed profiles were validated via real time quantitative PCR. Further, on-going metabolomic studies on phloem and EAB larval samples are providing additional insights into the metabolism of potential host factors. These results provide critical insights into the physiology-driven molecular mechanisms of EAB adaptation.