Physiological Responses to Spider Mite Infestation on Strawberries

The effect of various infestation levels expressed as mite-days, of Tetranychus urticae Koch on the chlorophyll content, transpiration, and photosynthesis of strawberry leaflets was studied. No reduction in chlorophyll content was observed at any infestation level, but transpiration and photosynthesis were reduced at low levels of 2.5 and 5.0 mite-days/cm 2 . Transpiration decreased rapidly by 42% at densities up to 15 mite-days/cm 2 , but at higher densities reduction was gradual and resulted in only an 11% reduction for an additional 35 mite-days/cm 2 . Photosynthesis was similarly affected at the low feeding levels (2.5–15 mite-days/cm 2 ) but continued to decrease linearly with increasing infestation levels resulting in a 60% reduction at 50 mite-days/cm 2 . The effect of mite feeding on stomatal opening and functional integrity of leaf tissue is discussed.