ANATOMY AND ULTRASTRUCTURE OF THE PIERCING-SUCKING MOUTHPARTS AND PARAGLOSSAL SENSILLA OF FRANKLINIELLA-OCCIDENTALIS (PERGANDE) (THYSANOPTERA, THRIPIDAE)

Scanning and transmission electron microscopy are used to elucidate the internal morphology of the feeding structures of the western flower thrips, Frankliniella occidentalis (Thysanoptera : Thripidae). The position of the single mandible and paired maxillary stylets, relative to one another within the mouthcone, are shown through sequential thin sectioning. Observation of thin sections of all 3 stylets demonstrate them to be innervated. Within the mandibular stylet are 3 dendrites extending its length, and 2 lateral dendrites in its wall. Each maxillary stylet contains 4 dendritic canals, each with one dendrite. The location of the cibarium within the mouthcone is examined and the attachments of its dilator muscles are shown. One to 3 dendrites, varying in functional type, are found in each paraglossal sensillum. The ultrastructural evidence presented suggests that some paraglossal sensilla have a dual chemosensory and mechanosensory function, while others are apparently solely mechanosensory. The significance of these findings relative to the feeding mechanisms of thrips and the possible function of stylet and paraglossal sensory structures in host location, feeding site selection and host choice are discussed.