Plant products are mainly stomach poisons, their contact toxicity reported against soft bodied insects and larvae is rather slow and reduced (probably because plant products must be ingested by pests to be effective).
systemic action is exerted when plant products are incorporated into soil or applied to plant parts, enhancing product bioefficacy and persistence in the field and makes the plant pest-resistant.
Generally, plant products act as antifeedants, repellents, growth regulators, sterilants, or oviposition deterrents or have toxic/pesticidal actions. Essential oils act as fumigants and contact poisons.
These actions depend on the dose/ concentration of the product and are related to the behavior and physiology of different systems of insects.