The relationship between the Yucca plant and the Pronuba moth is an example of obligate mutualism. Why?
It is obligate because neither can complete their life cycle without the other. The moth deposits its eggs in the locule of the ovary and pollinates the flower. The larvae feed on some of the developing seeds as they grow.
Ref: Image of a Yucca moth depositing eggs in the ovary of a Yucca flower.