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.
This study investigates the acaricidal, ovicidal, and repellent effects of the Tagetes patula Linn. (Asteraceae) leaf extract against both the adult female and egg stages of Tetranychus urticae Koch (Trombidiformes: Tetranychidae) under laboratory conditions. The Tagetes patula ethanolic leaf extract [TpEtOH70%] was screened for adulticide and ovicide bioassays in order to consider its acute toxicity. One sublethal concentration was used to assess egg-laying capacity (fecundity), repellent, and oviposition deterrent activities. The chemical characterization was conducted by gas chromatography-mass spectrometry (GC-MS) analysis to identify the TpEtOH70% bioactive components. Results showed that the LC50 value of TpEtOH70% leaf extract predicted by Probit analysis against T. urticae adult females at 24 h was 0.99%. The TpEtOH70% leaf extract showed a significant toxic effect as the highest mean mortality rates (± SE) of the treated adult females was 88.9 ± 3.7%. However, the TpEtOH70% leaf extract was insignificant in affecting the egg-laying capacity of the adult females treated with a sublethal dose of 0.5% even after 72 h. The TpEtOH70% leaf extract was classified repellent since the repellent index (RI) value was lower than 1 – SD. In addition, it had a high oviposition deterring effect based on a 100% reduction of the total number of eggs. The TpEtOH70% leaf extract had a significant ovicidal effect on T. urticae eggs, with 56.04% reduction in hatching. Five bioactive compounds from various classes of phytochemicals were identified in the TpEtOH70% leaf extract and the major compound was phytol (62.72%). This pioneering investigation reveals the adulticidal, ovicidal, and repellent activities of the TpEtOH70% leaf extract against T. urticae. A combination of multiple modes of action of different plant components may act alone or in synergism to delay the development of mite resistance.