Some aspects of plant penetration by Myzus persicae (Sulz.) nymphs (Homoptera, Aphididae)

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Abstract
The feeding penetrations of Myzus persicae (Sulz.) nymphs into tulip leaf epidermis, as shown by a study of stylets and tracks, may be intercellular, intracellular or stomatal with the former predominating. Contact between the stylet sheath or track and cell cytoplasm is at a maximum during intracellular entry but occurs to a limited extent during intercellular penetration due to partial rupture of the epidermal end walls. In the mesophyll, the stylet path is intercellular but a few cells were penetrated by tracks.Tracks vary in appearance according to the degree of confinement to which they have been subjected, the differing amounts of gelling saliva involved beingattributed to alterations in salivation rate or speed of penetration of the bundle. Seventypes of track were recognised, ranging from a thin membraneous to a thick lobular structure. The tracks have recognisable precursors in the stylet sheaths though differences between sheaths and tracks are evident, particularly where saliva is secreted during stylet withdrawal. In the vascular tissues, phloem and xylem are penetrated, often by repeatedlybranched tracks: the point of divergence of the arms of a branched track, in both mesophyll and vascular bundles, occurs only in large inter- or intracellular spaces where the lobular sheath or track is present. Three types of track are common in the vascular tissue:the lobular, the membraneous, and a saliva-filled type. The majority of stylet bundles terminate in the phloem. Rotation of the stylet bundle about its longitudal axis is generally absent.