The development of two-spotted spider mite (Tetranychus urticae Koch) injury on black currant leaves.

The leaf injury of two black currant cultivars caused by T. urticae feeding during the periods of 3, 6 and 10 days was studied. The density of mire population used in the experiment was about 0.6 mire per cm2. The observations were carried out on: fresh green leaves; leaves with removed pigments, by boiling in 80% alcohol, cross sections of leaf tissues. The intensity of photosynthesis of injured leaves was also studied. After a short period of spider mite feeding the symptoms of injury on fresh green leaves were barely visible. After chlorophyll extraction the brown spots on the leaf-blade, in the place of mite feeding were noticed. The size of brown area was related to the period of mite feeding. Cytological observations indicated that within mite injured area both spongy and palisade mesophyll cells were filed with safranin positive material before they were destroyed. The photosynthesis was strongly inhibited in the leaves with minor visible symptoms of mite feeding.