Technical Abstract: Genomic analyses of several leafhoppers identified the first leafhopper delta-9 desaturase. Identification of important gene transcripts within insect pests permits them to be targeted with RNA interference, RNAi, strategies. The glassy-winged sharpshooter, GWSS (Hemiptera: Cicadellidae; Homalodisca vitripennis) and other leafhoppers are vectors of Xylella fastidiosa, a xylem-limited bacteria that causes economic loss in grapevine and other woody agricultural fruit, nut, and ornamental crops. Management of Pierce’s disease currently depends heavily upon insecticides. To extend current IPM programs alternatives need to be developed which can work within these programs. The GWSS desaturase cDNA encodes a 367 protein with 71% identity to Acheta domesticus desaturase, and greater than 50% identity with other insect delta 9 desaturases. In silico analyses places GWSS delta 9 desaturase in the Family 1 of ProDomain fatty acid desaturases and predicts the protein is a Palmitoyl-CoA delta 9 desaturase-1 (accession number: AY588067). Expression analyses resulted in lack of detection of expression in eggs. All instars, 1-5th, expressed delta 9 desaturase showing a significant increase in the 5th instar and adults which correlated to increased feeding on a widening host plant range to complete development. There was no significant difference in expression levels among 1-4th instars. The 5th instars had significantly increased levels of desaturase from previous instars, while adults expressed significantly greater levels from all other life stages. Adult females showed a greater than 7 fold increase over 1-4th instars, with a greater than 3 fold increase over 5th instars. There was no significant difference to adult males. This is the first desaturase identified from leafhoppers and builds upon our understanding of the biological pathways in leafhopper fitness.