The distribution of a typhlocybine leafhopper, Ribautiana ulmi (Homoptera: Cicadellidae) on a specimen wych elm tree

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Abstract
Higher numbers of feeding and resting Ribautiana ulmi (L.) were found on the more highly illuminated areas of the canopy of a wych elm tree, Ulmus glabra Huds. cv. Camperdownii. Higher numbers were also found on the basal leaves of each branch when compared with the distal leaves, and on exposed areas of individual leaves when compared with the shaded areas which they overlapped. Leaf thickness, tannin concentrations and leaf toughness were greater, and water content lower, in leaves from exposed areas of the canopy than from shaded ones. R.ulmi feeds selectively on the contents of the palisade mesophyll cells, and therefore was assumed to ingest the highest available levels of tannins.