What role do fully transformed insects play in nature?

This question must be answered by recalling specific representatives of different detachments undergoing a complete transformation.
1) Fleas – are parasites of mammals, carry diseases dangerous to humans and other animals
2) Diptera are, for example, flies, midges, horseflies. They are predators (consuming blood is considered predation if the animal does not use another organism as its home) and also carry diseases. However, there is also a positive side: many are engaged in pollination.
3) Coleoptera, or Beetles. The detachment is very large, therefore, among their roles are soil-forming, and sanitary, and pollination. True, parasitic worms do not leave these little laborers alone.
4) Hymenoptera are ants, bees, bumblebees, wasps. The former loosen the soil and increase its fertility, the latter three are active pollinators.
5) Lepidoptera, or Butterflies. They also pollinate.
Of course, all of these insects are part of the food chain.