The vegetable spider mite, Tetranychus neocaledonicus (André, 1933) has been recognized as a highly polyphagous pest, infesting 432 species of host plants (Bolland et al., 1998) of varied economic categories. During the present study, the mite was found to infest the medicinal as well as spice crop, Mentha rotundifolia L. Samples of mite infested and healthy leaves of M. rotundifolia were collected from the Botanical Garden of the Calicut University Campus and the extent of damage induced by T. neocaledonicus was estimated by assessing the loss of chlorophyll, carotenoids and photosynthetic efficiency. Apart from the above, the host plant stress induced by the mite infestation was also quantitated by estimating the levels of phenol in infested and healthy leaves of M. rotundifolia. Arnon’s (1949) method was followed for estimating the chlorophyll and carotenoid pigments and the photosynthetic efficiency was measured using the Handy Photosynthetic Efficiency Analyser. Total phenol content of the mint leaves was estimated with Folin-Ciocalteau reagent. Results of the study enabled to record a significant quantitative reduction ((P<0.01) in chlorophyll a (31.22%), chlorophyll b (34.42%), total chlorophyll (32.31%) and carotenoids (24.48%) owing to mite infestation. A significant reduction (P<0.05) in the photosynthetic efficiency of the leaves was also evidenced, by recording the Fv /Fm value of 0.8256 for uninfested leaves against a reduced value of 0.5754 for mite infested leaves. The study enabled to record a significant increase (P<0.01) in total phenol content of infested leaves, which showed an increase of 50.7%.
