The population dynamics of Tetranychus urticae (two-spotted spider mite – TSSM) are influenced by environmental factors, which were investigated to identify methods limiting the development and harmfulness of this pest. This paper presents findings from a laboratory study on the effect of spraying with water-based extracts of Mentha piperita and Tagetes patula plants on the growth rate of TSSM larvae and nymphs. The time required for the transformation of the larvae into protonymphs was longer for T. patula water- based extracts than extracts from M. piperita. Differences in the time of transformation from the nymphal stage to adult TSSM were also observed depending on the plant waterbased extracts, their concentration, and the host plant on which nymphs were developing. The use of 100 g ∙ l-1 French marigold extract was associated with longer transformation time of nymphs on discs of pea leaves than all tested concentrations of French marigold extract applied to sugar beet leaves. Ten percent of the extracts from peppermint plants had a stronger limiting effect on TSSM nymphs on pea leaves than on bean or sugar beet leaves.

Tetranychus urticae (Acari: Tetranychidae) infesting many plants but Mentha viridis L., and Mentha piperita L., were low in number of infestation. Therefore the objective of this study was to identify the resistance of M. viridis and M. piperita plants against T. urticae by studying the external shape and internal contents of those plants. For morphological studies, dried leaves were covered with gold utilizing an Edwards Scan coat six sputter-coater. For histological studies, arrangements of Soft Tissue technique were used. For phytochemical studies, the plants were cut, dried and then high performance liquid chromatography (HPLC) was used. While feeding the mites were collected from the area between oily glands, trichomes and respiratory stomata in both mint species. The most important leaf structures in aromatic plants are the oily glands found on the external part of the leaves (both upper and lower epidermis). The number of oil glands in M. viridis leaves was greater than in M. piperita; the trichomes on the epidermis of M. viridis were greater in number than in M. piperita; the spongy mesophyll in M. viridis was much thicker than in M. piperita. The essential oils in the leaves of both mint species contained 71 compounds representing 99.61% of the total oil constituents identified from M. viridis before infestation, and 90.95% after infestation, and about 99.65% from M. piperita before infestation, and 99.98% after infestation.

We investigated the antioxidant defense mechanism, metal uptake and lipid peroxidation (LPO) levels at different leaf positions in Mentha piperita L. grown in Mn2+-deficient and control conditions. Under manganese deficiency the activity of superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GuaPOX) and the content of ascorbate, chlorophyll, and carotenoid under Mn2+ deficiency were significantly lower than in the control for all leaf positions. SOD activity correlated positively with Mn2+ uptake. Fe2+ uptake was inhibited by Mn2+ deficiency. During early stages of Mn2+ deficiency, M. piperita leaves showed relatively more antioxidant activity and lower LPO. Towards the final stages of the treatment period, comparatively lower SOD, CAT and GuaPOX activity and higher LPO levels accelerated the senescence process.