CHLOROPHYLL FLUORESCENCE AND LEAF CHLOROPHYLL CONTENT OF BEAN-LEAVES INJURED BY SPIDER-MITES (ACARI, TETRANYCHIDAE)

The use of chlorophyll fluorescence as a method for detecting and moni toring plant stress arising from Tetranychus urticae (Koch) feeding in jury was investigated. The effect of mite density (1-32 mites per 1.5 cm(2) of leaf) and the duration of the feeding period (1-5 days) on th e chlorophyll fluorescence parameters of bean (Phaseolus vulgaris) lea ves were examined. Changes in chlorophyll fluorescence parameters were dependent both on mite density and duration of feeding. Decreases in F-o, the initial fluorescence and F-m, the maximum fluorescence led to a decrease in the ratio of variable to maximum fluorescence, F-v/F-m. The decrease in F-v/F-m is typical of the response of many plants to a wide range of environmental stresses and indicates a reduced efficie ncy of photosystem II (PSII) photochemistry. T-1/2, which is proportio nal to the pool size of electron accepters on the reducing side of PSI I, was also reduced in response to mite-feeding injury. The leaf chlor ophyll content decreased with increasing mite density and duration of feeding but did not appear to contribute to the decrease in F-v/F-m. C hlorophyll fluorescence is an effective method for detecting and monit oring stress in T. urticae-injured bean leaves.