Developing Sustainable Strategies to Manage Spotted Wing Drosophila in United States Fruit Crops

Significance: Spotted wing drosophila (SWD, Drosophila suzukii) has become a serious pest of soft skinned fruits. Critical life traits such as mating, host location and predator avoidance are olfactory-driven in Drosophila fruit flies and we have thus far identified key attractants derived from the filed isolates of SWD associated yeasts. A blend of the two chemical, isobutyl and isoamyl acetate has been field evaluated and we are further refining the dose and the blend. In addition, genome and whole olfactory transcriptome data has identified unique expansion of two genes (Or23a and 67a) that are under positive selection, and a significant modulation of transcripts between SWD virgin and gravid (infective) stages. We are currently cloning the 2 genes and are set to functionally characterize them with the planned purchase of oocyte expression system. Proposed aims (re-adjusted based on the progress already made): Aim 1: Identification of natural and biologically relevant odorant ligands for SWD We have almost completed the study on yeast derived attractants, we are in the process of isolating and identifying the sex pheromones that will further enhance the efficiency and specify of yeast derived attractive blend. This will be accomplished by employing gas chromatography linked electroantennogram detection (GC-EAD) and GC-single sensillum recordings (GC-SSR), two techniques in which VOCs are separated on a high-resolution GC column and effluents split so as to allow one fraction to be analyzed by Flame Ionization Detector (FID) or Mass Spectrometry (MS) and the other to be directed across the antenna or ORN of a SWD live fly acting as a biological sensing element. Behavior will be assessed using simple choice assays as well as a four-arm olfactometer to individual constituents and their natural blends. Aim 2: Analysis of the Odorant Receptor (Or) repertoire of SWD We have identified two olfactory genes, OR23a and OR67a, that are uniquely expanded in the SWD lineage and are under positively selection. Antennal transcriptome data further supported the potentially critical role of these genes since they are significantly upregulated during the gravid stage of SWD when the fly locates a fresh fruit to oviposit. We propose to functionally characterize the duplicated Ors, and identify the critical ligands that excite these Ors. This work will identify the genetic history of SWD and reveal its recent evolution as it adapts to its new environment, especially the unique olfactory landscape.