When attacked by arthropods, pathogen or even mechanically damaged, tomato plants may systemically synthesize proteinase inhibitors (PI’s) in response to this damage. Proteinase inhibitors are known to be efficient in blocking the attack of arthropods to the plants by blocking proteolyses in its midgut, which can reduce their growth and reproduction. This study focused on determining whether the spider mite Tetranychus evansi induces PI’s in tomato plants. The induction of PI’s in tomato plants upon attack by T. evansi was measured according to the following treatments: (I) damaged leaves, (II) induced leaves, (III) damaged leaves control and (IV) induced leaves control. Each treatment was replicated four times, resulting in a total of eight plants. For the treatments I and II, two leaves of a plant were infested with T. evansi and a non-drying glue was applied to the petiole of these leaves to prevent mites from moving to the other leaves of the plant, which were used as induced, but undamaged leaves. For each treated plant, a control was prepared, consisting of a clean tomato plant of the same age as the treated plant, and with glue applied to the petiole of two leaves, but without mites (treatment III) and the other two remaining leaves were kept without glue (treatment IV). The plants were kept in mite-proof screen cages in a greenhouse. Seven days after infestation with mites, were collected samples (300 mg) according to each treatments. The samples were frozen in liquid nitrogen and kept in a -70 °C freezer. The extract was obtained by grounding to powder the samples in liquid nitrogen. The powder was homogenized in 1000 µl extraction buffer (Tris Hcl pH 8,2 com 20mM de CaCl₂ 1:3 w/v). The liquid was centrifuged at 17200g for 30 min at 4 °C, and collecting the supernatant, which was used to measure the trypsin activity of the samples. It was measured by using BApNA 1,2 mM and total protein concentration was measured in A_280. The treatments I and II, had the lower reduction of trypsin activity when compared to its respective controls, which characterizes a lower production of inhibitor by the plants on the treatments where the leaves were damaged and systemically induced. It is known that T. evansi spins a profuse, chaotically structured web over their colonies and this web is composed by amino acids, as well as PI’s. Our results suggest that the mite would be using the amino acids from the inhibitor on its metabolism, as well as to produce web.