Weed and wild plants are not affected by insects and pests because they are the unwanted plants which can grow and take the nutrition from the other plants and pest.
Because though the waste weed and wild plants are eaten by the pests(like insects),they have a strong regeneration capacity as the roots are intact and only leaves are eaten,hence they grow fast within a short span of time.

Hope u understood clearly :)
pls mark as the best if u understood it clearly:)
2 5 2