SCANNING ELECTRON-MICROSCOPIC OBSERVATIONS OF THE MOUTHPARTS AND FEEDING MARKS OF THRIPS-PALMI KARNY (THYSANOPTERA, THRIPIDAE)

The structure of the mouthparts of adult female Thrips palmi KARNY was examined under a scanning electron microscope. The mouthparts form a broad proboscis called the mouthcone consisting of anteclypeus, labrum, maxillary lobes and labium. The mouthcone apex is usually covered by a membraneous labial lobe, paraglossa, with more than 10 pairs of hooks (possibly sensory hairs). When feeding, the insect retracts the covering paraglossa laterally and protracts three stylets on the exposed apex. The stouter mandibular stylet, about 1.7 mum in diameter at the base, is thought to puncture holes through the plant epidermis. The slender, paired maxillary stylets seem to combine with each other lengthwise to form a long tube, about 1.7 mum in diameter, for sucking cell sap. A large concave structure, possibly a labral pad, is located around the stylets on the exposed mouthcone apex. After examination of injured leaves, only a few feeding marks, about 2 mum in diameter, were found on all collapsed epidermal cells. No destroyed, torn or gashed cells, or exposed cell content were observed at all. The morphology of mouthparts, and the feeding marks on injured leaves indicate that T. palmi is a true sap feeder with no biting behavior.