Final answer:
None of the options provided (stomach poison, systemic, contact) represent a mode of action that is NOT utilized by pesticides. Instead, all these are established modes through which pesticides can act on pests.
Step-by-step explanation:
The question asks which option is NOT a mode of action of pesticides. The options given are: stomach poison, systemic, and contact. These modes of action describe different ways that pesticides can affect pests. A stomach poison affects pests when they ingest the treated plant material. A systemic pesticide is one that gets absorbed by the plant and distributed throughout its tissues, reaching all parts of the plant, which then affects pests that feed on it. A contact pesticide affects pests upon direct contact. Therefore, all the options listed represent modes of action of pesticides, so the correct answer is that all are modes of action.