Transcriptome profiling reveals the developmental regulation of NaCl-treated Forcipomyia taiwana eggs

The biting midge, Forcipomyia taiwana, is one of the most annoying blood-sucking pests in Taiwan. Their bites often cause significant itching. Normally, eggs laid on a moist surface with fresh water darken, or melanize, during development. However, eggs laid on a moist surface with slightly saline water (0.025 M NaCl) remain unmelanized and do not hatch. To better understand the molecular processes affected by the saline environment, we conducted RNA sequencing of control eggs and of eggs exposed to high concentrations of NaCl (0.25 M) solution. Analysis of this data revealed thousands of differentially expressed transcripts, many associated with development and metabolism. Additionally, we observed that the laccase2 and DCE/Yellow genes, two genes involved in the synthesis of melanin, were down regulated in NaCl treated eggs, and thus likely explaining their lack of melanization.