PRECIBARIAL AND CIBARIAL CHEMOSENSILLA IN THE WESTERN FLOWER THRIPS, FRANKLINIELLA-OCCIDENTALIS (PERGANDE) (THYSANOPTERA, THRIPIDAE)

The internal anatomy of the mouthcone of the western flower thrips, Fr ankliniella occidentalis (Pergande) (Thysanoptera : Thripidae), was ex amined by scanning and transmission electron microscopy to show locati on, number and fine structure of the precibarial and cibarial chemosen silla. Four precibarial sensilla are located approximately 12 mum from the tip of the mouthcone, proximal to where the maxillary stylets div erge on their retraction. The cibarium has 20 sensilla, 18 on the epip haryngeal sclerite and 2 on the hypopharyngeal sclerite. The fine stru cture of individual neurons and their termination at a pore opening in to the precibarium and cibarium, respectively, supports a chemosensory function. Ultrastructure of the neurons is similar to that of preciba rial and cibarial gustatory chemosensilla found in other piercing-suck ing insects, while the number and location of these structures vary wi dely. Their importance in thrips feeding is discussed and a flowchart of possible thrips host plant selection behavior is proposed.